| 1. |
- Abou Rafee, Sameh Adib, et al.
(författare)
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Hydrologic response to large-scale land use and cover changes in the Upper Paraná River Basin between 1985 and 2015
- 2021
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Ingår i: Regional Environmental Change. - : Springer Science and Business Media LLC. - 1436-3798 .- 1436-378X. ; 21:4
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Tidskriftsartikel (refereegranskat)abstract
- The Upper Paraná River Basin (UPRB) has undergone remarkable land use and cover changes (LUCC) in recent decades. This paper analyses the hydrologic response to LUCC in the UPRB between 1985 and 2015, using the Soil and Water Assessment Tool (SWAT) model. The impacts of LUCC were examined for annual, wet, and dry season (both during calibrated and validated periods) between 1984 and 2015. The most substantial LUCC were the extensive reduction of the cerrado and the expansion of agriculture areas. The simulations demonstrated that the LUCC caused important changes in basin hydrology. For instance, an increase (decrease) of surface runoff in the wet (dry) season at most UPRB subbasins was observed. In addition, the simulation results revealed a reduction in actual evapotranspiration and an increase in soil moisture in the annual and wet season. Consequently, most of the major rivers of the basin presented an increase (decrease) in their discharge in the wet (dry) period. The major changes in the hydrologic components were observed in the central-western and southern parts of the UPRB. At the river mouth of the UPRB, the LUCC led to an increase in long-term mean discharge values of 4.2% and 1.1% in the annual and wet season and a decrease of about 2.2% in the dry period. This study provides a large-scale modeling and valuable information that could be used to improve planning and sustainable management of future water resources within the basin.
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| 2. |
- Ahlström, Anders, et al.
(författare)
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GCM characteristics explain the majority of uncertainty in projected 21st century terrestrial ecosystem carbon balance
- 2012
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Ingår i: Biogeosciences Discussions. - : Copernicus GmbH. - 1810-6277. ; 9, s. 13685-13712
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- One of the largest sources of uncertainties in modelling of the future global climate is the response of the terrestrial carbon cycle. Studies have shown that it is likely that the extant land sink of carbon will weaken in a warming climate. Should this happen, a larger portion of the annual carbon dioxide emissions will remain in the atmosphere, and further increase global warming, which in turn may further weaken the land sink. We investigate the potential sensitivity of global terrestrial ecosystem carbon balance to differences in future climate simulated by four general circulation models (GCMs) under three different CO2 concentration scenarios. We find that the response in simulated carbon balance is more influenced by GCMs than CO2 concentration scenarios. Empirical orthogonal function (EOF) analysis of sea surface temperatures (SSTs) reveals differences among GCMs in simulated SST variability leading to decreased tropical ecosystem productivity in two out of four GCMs. We extract parameters describing GCM characteristics by parameterizing a statistical emulator mimicking the carbon balance response simulated by a full dynamic ecosystem model. By sampling two GCM-specific parameters and global temperatures we create 60 new "artificial" GCMs and investigate the extent to which the GCM characteristics may explain the uncertainty in global carbon balance under future radiative forcing. Differences among GCMs in the representation of SST variability and ENSO and its effect on precipitation and temperature patterns explain the majority of the uncertainty in the future evolution of global terrestrial ecosystem carbon in our analysis. We suggest that the characterisation and evaluation of patterns and trends in simulated SST variability should be a priority for the further development of GCMs, in particular as vegetation dynamics and carbon cycle feedbacks are incorporated.
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| 3. |
- Ahlström, Anders, et al.
(författare)
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GCM characteristics explain the majority of uncertainty in projected 21st century terrestrial ecosystem carbon balance
- 2013
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4189. ; 10:3, s. 1517-1528
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Tidskriftsartikel (refereegranskat)abstract
- One of the largest sources of uncertainties in modelling of the future global climate is the response of the terrestrial carbon cycle. Studies have shown that it is likely that the extant land sink of carbon will weaken in a warming climate. Should this happen, a larger portion of the annual carbon dioxide emissions will remain in the atmosphere, and further increase global warming, which in turn may further weaken the land sink. We investigate the potential sensitivity of global terrestrial ecosystem carbon balance to differences in future climate simulated by four general circulation models (GCMs) under three different CO2 concentration scenarios. We find that the response in simulated carbon balance is more influenced by GCMs than CO2 concentration scenarios. Empirical orthogonal function (EOF) analysis of sea surface temperatures (SSTs) reveals differences among GCMs in simulated SST variability leading to decreased tropical ecosystem productivity in two out of four GCMs. We extract parameters describing GCM characteristics by parameterizing a statistical emulator mimicking the carbon balance response simulated by a full dynamic ecosystem model. By sampling two GCM-specific parameters and global temperatures we create 60 new "artificial" GCMs and investigate the extent to which the GCM characteristics may explain the uncertainty in global carbon balance under future radiative forcing. Differences among GCMs in the representation of SST variability and ENSO and its effect on precipitation and temperature patterns explain the majority of the uncertainty in the future evolution of global terrestrial ecosystem carbon in our analysis. We suggest that the characterisation and evaluation of patterns and trends in simulated SST variability should be a priority for the further development of GCMs, in particular as vegetation dynamics and carbon cycle feedbacks are incorporated.
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| 4. |
- Ali Maher, Osama, et al.
(författare)
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Comparison between two extreme NAO winters and consequences on the thermal regime of Lake Vendyurskoe, Karelia
- 2005
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Ingår i: Journal of Hydrometeorology. - 1525-755X. ; 6:5, s. 775-783
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Tidskriftsartikel (refereegranskat)abstract
- For 10 consecutive winters, measurements were carried out in Lake Vendyurskoe, Karelia, Russia. The aim of these measurements was to investigate some of the physical processes in this small shallow lake during its ice-covered period. Detailed measurements of ice thickness and condition, snow thickness, water temperature, salt content, and currents were developed into a database. Within this database are the winters 1994/95 and 1995/96, which are characterized by a very sharp change between positive and negative phases of the North Atlantic Oscillation (NAO). This note investigates and compares the effects of these two NAO phases on the regional climate and their relation to the thermal regime of Lake Vendyurskoe. It became clear that the ice-covered period length did not vary much from one winter to the other; however, a large difference was observed in the maximum average ice cover thickness and in the average water temperature at ice formation ( e. g., larger thickness and colder water temperature during the 1995/ 96 winter).
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| 5. |
- Berndtsson, Ronny, et al.
(författare)
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Hydrology for Environmental Engineers
- 2014
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Bok (övrigt vetenskapligt/konstnärligt)abstract
- This textbook aims to provide a comprehensible introduction to Engineering Hydrology for environmental engineering students. The book comprises of 8 chapters which provide a holistic view of hydrology, seen as the water transport in nature with human influence, and deal with the main hydrological systems and processes. Each chapter ends with a few engineering examples together with a discussion of calculation methods, followed by further engineering problems. The book has been compiled from earlier hydrology textbooks from the Department of Water Resources Engineering at LTH, Lund University, Sweden. The most important contributions are from Lars Anderberg (“Kort introduktion till hydrologi”) and Rolf Larsson (“Övningsexempelsamling avsett för Väg&vatten-byggnadsingenjörer vid LTH”).
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| 6. |
- Berndtsson, Ronny, et al.
(författare)
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Riseberga Restoration Project
- 2014
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This project is designed as a typical consultancy work for Environmental Engineering students at the Faculty of Engineering (LTH), Lund University, Sweden. It gives students a feeling of a possible future work by being a practical training in solving a complex environmental problem involving hydrological and ecological challenges. Additionally, the project work provides training of critical thinking, engineering techniques and presentation of technical reports. The outcome of this work is a proposal for restoration of a wetland at Riseberga River Basin in Malmö, southern Sweden. It will be presented as a report as well as an oral presentation of the restoration plan at the end of the semester by each group.
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| 7. |
- Bertacchi Uvo, Cintia
(författare)
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Analysis and regionalization of northern european winter precipitation based on its relationship with the North Atlantic oscillation
- 2003
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Ingår i: International Journal of Climatology. - : Wiley. - 1097-0088 .- 0899-8418. ; 23:10, s. 1185-1194
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Tidskriftsartikel (refereegranskat)abstract
- The relationship between the North Atlantic oscillation (NAO) and winter temperature and precipitation over northern Europe has long been known. However, its strength is variable within this region. In this paper, an analysis of the regional variability of the influence of the NAO on winter precipitation in northern Europe is developed using empirical orthogonal function analysis, cluster analysis and simple correlation. Results show that precipitation in most of the region studied is affected by the NAO, although with varying intensity. The NAO strongly influences winter precipitation along the Norwegian coast, in northern Sweden and in southern Finland. It is evident that the region on the lee side of the Scandes (the mountain chain between Norway and Sweden) is protected from the effects of the moist western winds from the Atlantic that, in turn, are strongly related to the NAO. As a result, precipitation in this shielded area is mainly related to southeasterly winds. Copyright (C) 2003 Royal Meteorological Society.
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| 8. |
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| 9. |
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| 10. |
- Bertacchi Uvo, Cintia
(författare)
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Influence of Sea Surface Temperature on Rainfall and Runof in Northeastern South America: Analysis and Modeling
- 1998
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This work represents an amalgam of a group of studies with the purpose of understanding the influence of the Pacific and Atlantic sea surface temperature on precipitation and river discharge in Northeastern South America. Sea surface temperature is a good representative of phenomena such as ENSO that, in turn, cause worldwide climate variability. The patterns of the Atlantic Ocean sea surface temperature anomaly also plays a very important role in the precipitation over the neighboring regions and a special investigation was also carried out to better understanding this influence. The influence of these oceans' sea surface temperature on the intraseasonal variability of precipitation in Northeast Brazil was also a particular subject of study. Statistical methods were largely used both during these investigations and in the development of models for forecasting discharge long term in advance at some sites in the Amazon, Orinoco and Tocantins River Basins. Sea surface temperature anomalies in both oceans significantly influence precipitation over northeastern South America. The Atlantic Ocean, however, plays a more important role in the case of precipitation over Northeast Brazil while the Pacific Ocean seems to have stronger influence over eastern and northern Amazonia. As a result of changes in precipitation, the river discharge in the Amazon Region is also influenced by changes in sea surface temperature patterns. The discharge of rivers located to the north of the Amazon River is mainly influenced by the Pacific sea surface temperature while the Atlantic influences the rivers to the south of the Amazon River. This influence could be clearly observed using the forecast models. Two different methodologies were used to develop forecast models: Canonical Correlation Analysis and Artificial Neural Network. The first is a linear technique and the second a non-linear one. In both cases, the models developed using Pacific sea surface temperature were better at forecasting discharge at sites to the north of the Amazon River and those developed from Atlantic sea surface temperature at forecasting discharges at sites to the south of the Amazon River. Even though the use of a non-linear technique improved the accuracy of the models in general, it considerably improved the capacity of Atlantic sea surface temperature to forecast discharge. This general improvement was to some degree expected considering the very complex and non-linear mechanisms that transform precipitation into discharge.
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| 11. |
- Bertacchi Uvo, Cintia, et al.
(författare)
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North Atlantic oscillation; a climatic indicator to predict hydropower availability in Scandinavia
- 2002
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Ingår i: Nordic Hydrology. - 0029-1277. ; 33:5, s. 415-424
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Tidskriftsartikel (refereegranskat)abstract
- Climate variability and climate change are of great concern to economists and energy producers as well as environmentalists as both affect the precipitation and temperature in many regions of the world. Among those affected by climate variability is the Scandinavian Peninsula. Particularly, its winter precipitation and temperature are affected by the variations of the so-called North Atlantic Oscillation (NAO). The objective of this paper is to analyze the spatial distribution of the influence of NAO over Scandinavia. This analysis is a first step to establishing a predictive model, driven by a climatic indicator such as NAO, for the available water resources of different regions in Scandinavia. Such a tool would be valuable for predicting potential of hydropower production one or more seasons in advance.
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| 12. |
- Bravo, J. M., et al.
(författare)
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Incorporating Forecasts of Rainfall in Two Hydrologic Models Used for Medium-Range Streamflow Forecasting
- 2009
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Ingår i: Journal of Hydrologic Engineering. - 1084-0699. ; 14:5, s. 435-445
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Tidskriftsartikel (refereegranskat)abstract
- This study reports on the performance of two medium-range streamflow forecast models: (1) a multilayer feed-forward artificial neural network; and (2) a distributed hydrologic model. Quantitative precipitation forecasts were used as input to both models. The Furnas Reservoir on the Rio Grande River was selected as a case study, primarily because of the availability of quantitative precipitation forecasts from the Brazilian Center for Weather Prediction and Climate Studies and due to its importance in the Brazilian hydropower generating system. Streamflow forecasts were calculated for a drainage area of about 51,900 km(2), with lead times up to 12 days, at daily intervals. The Nash-Sutcliffe efficiency index, the root-mean-square error, the mean absolute error, and the mean relative error were used to assess the relative performance of the models. Results showed that the performance of streamflow forecasts was strongly dependent on the quality of quantitative precipitation forecasts used. The artificial neural network (ANN) method seemed to be less sensitive to precipitation forecast error relative to the distributed hydrological model. Hence, the latter presented a better skill in flow forecasting when using the more accurate perfect precipitation forecast. The conceptual hydrological model also demonstrates better forecast skill than ANN models for longer lead times, when the representation of the rainfall-runoff process and of the water storage in the watershed becomes more important than the flow routing along the drainage network. In addition, results obtained by incorporating a quantitative precipitation forecast in both models performed better than the current streamflow obtained by the Brazilian national electric system operator using statistical models which do not utilize information on precipitation, whether observed or forecast.
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| 13. |
- Cherry, J, et al.
(författare)
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Impacts of the North Atlantic Oscillation on Scandinavian hydropower production and energy markets
- 2005
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Ingår i: Water Resources Management. - : Springer Science and Business Media LLC. - 0920-4741 .- 1573-1650. ; 19:6, s. 673-691
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Tidskriftsartikel (refereegranskat)abstract
- Dramatic swings in the North Atlantic oscillation (NAO) during the 1990s motivated the authors to build a statistical model of NAO impacts on hydropower production and energy markets in Scandinavia. Variation in the NAO index is shown to explain 55% of the variance of streamflow in Norway and up to 30% of the variance in Norway's hydropower output. It is also possible to identify the influence of NAO anomalies on electricity consumption and prices. Government liberalization allowed a financial market to grow around the international trading of electricity, which in Norway is produced almost entirely from hydropower. The model offers a possible tool for predicting the effects of future NAO movements on hydropower production and energy prices in Scandinavia. The potential influence of skillful climate prediction is discussed.
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| 14. |
- Clarke, Robin T., et al.
(författare)
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Comparison of methods for analysis of extremes when records are fragmented: A case study using Amazon basin rainfall data
- 2009
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Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694. ; 368:1-4, s. 26-29
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Tidskriftsartikel (refereegranskat)abstract
- The analysis of annual extremes of hydrological and meteorological variables is frequently complicated by the presence of gaps in record, and when records are not only fragmented but also short, it is necessary to utilize to the full the information contained in them. One method is to abstract for statistical analysis all extreme events whose peaks exceed a pre-selected threshold value, but the threshold must be carefully chosen if "clumps" of peaks are to be avoided. A common alternative is a statistical analysis of maxima in years that are complete, possibly including in the analysis values from incomplete years according to some empirical rule. A plausible probability distribution has been proposed by [Jones, D.A., 1997. Plotting positions via maximum likelihood for a non-standard situation. Hydrol. Earth Syst. Sci. 1, 357-366] for the extremes observed in incomplete years, which takes into account not only the proportion of record that is missing within an incomplete year, but also the effect of seasonality. As part of a larger study on the hydrology of the Amazon basin, this paper uses 484 records with length not less than 12 years from an extensive network of 750 rain gauges, to compare the method proposed by Jones (termed the DAJ method) with the following alternative procedures: (i) using only complete years of record and (ii) including years with less than 20% missing record, as if they were complete. Using the large-sample variance calculated for the annual maximum one-day rainfall with 100-year return period (P-100), the method proposed by Jones is shown to give smaller standard errors than either of the alternatives. Using the number of years in each record to calculate weighted mean variances over the 484 records, the mean standard errors of Ploo obtained by methods (i) and (ii) were 1.25 and 1.06 times the mean standard error given by the DAJ method. The precision of estimates obtained by the latter method was therefore better than either alternative. (c) 2009 Elsevier B.V. All rights reserved.
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| 15. |
- Coelho, C.A.S., et al.
(författare)
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Exploring the impacts of the tropical Pacific SST on the precipitation patterns over South America during ENSO periods
- 2002
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Ingår i: Theoretical and Applied Climatology. - : Springer Science and Business Media LLC. - 1434-4483 .- 0177-798X. ; 71:3-4, s. 185-197
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Tidskriftsartikel (refereegranskat)abstract
- Summary Previous studies on precipitation over South America that strongly support the existence of links between precipitation and SST anomalies in the Pacific Ocean have identified specific regions where the ENSO signal is particularly stronger. Northeast of Brazil and some parts of southern South America are examples of these regions. However, the same attention was not taken to identify which regions in the Central and East Pacific ocean are better correlated with the South America precipitation during extreme ENSO events, and also which are the transition regions of the precipitation signal over South America during these events. Coincident periods of ENSO events for both SST over the tropical Pacific ocean and monthly precipitation sums from many observational stations over South America were selected and analyzed. Two statistical methods were used for the data analysis: Singular Value Decomposition (SVD) and Simple Linear Correlation (SLC). The SVD results for warmer events in the Pacific corroborate previous ones and also clearly identified a transition region between the drier conditions in the Northeast of Brazil and the wetter conditions in the Southeast/South of Brazil. Transition regions were also determined over Peru and central Amazon. The SLC results indicated that the SST anomalies in the tropical east Pacific ocean has the strongest influence in the South American precipitation during El Niño events. During La Niña events the central area of the Pacific, around 180°, has shown a more significant influence.
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| 16. |
- da Paz, Adriano Rolim, et al.
(författare)
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Seasonal precipitation forecast based on artificial neural networks
- 2010
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Ingår i: Computational Methods for Agricultural Research : Advances and Applications - Advances and Applications. - : IGI Global. - 9781616928711 ; , s. 326-354
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Bokkapitel (refereegranskat)abstract
- Agriculture is vulnerable to the interannual climate variability and to its unpredictability, in such a way that most agricultural decisions taken within the time horizon of several months are made in a conservative manner, supposing a near-pessimist scenario. The improvement of climate prediction may help the strategic view, mitigating unwanted impacts and taking advantage of favorable conditions. This chapter presents the development of an Artificial Neural Network (ANN) model for seasonal precipitation forecast based on climate indices, focusing on the practical aspects of selecting the best predictors, defining ANN architecture, data handling and ANN training and validation. The study case is the Pardo/Mogi-Guaçu rivers watershed in Brazil, which is characterized by intense sugarcane plantation for both ethanol and sugar industries. The results demonstrate how the methodology for seasonal precipitation forecast based on ANN can be particularly helpful, with the use of available time series of climate indices.
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| 17. |
- Engstrom, Johanna, et al.
(författare)
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Effect of Northern Hemisphere Teleconnections on the Hydropower Production in Southern Sweden
- 2016
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Ingår i: Journal of Water Resources Planning and Management. - 0733-9496. ; 142:2
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Tidskriftsartikel (refereegranskat)abstract
- Approximately 50% of Sweden's electricity is produced by hydropower. This makes energy production in the country vulnerable to factors affecting water availability. Research has shown a positive correlation between the North Atlantic Oscillation (NAO) and hydropower production in Norway and northern Sweden during winter months. The correlation is, however, weaker in southern Sweden, which indicates that there might be other low-frequency atmospheric drivers (teleconnections) affecting this area. The aim of this paper is to analyze the natural climate forcing that affects hydropower production in southern Sweden on a seasonal basis. This knowledge may be of key importance in improving long-term (seasonal to yearly) water management and planning for electricity production in southern Sweden. The Spearman correlation coefficient was calculated between the principal component time series of electricity production (1999-2010) from 17 hydropower stations in 5 different rivers located in southern Sweden and 5 different teleconnection indices: the NAO, East Atlantic (EA), East Atlantic/Western Russia (EA/WR), Scandinavia (SCA), and Polar/Eurasia (POL). Results show that the impact of teleconnections on hydropower electricity production varies with season. In winter, the NAO shows the strongest positive relation with hydropower electricity production, explaining 24% of the variability in production, while the SCA has an almost as strong (15%) opposite effect. During spring and summer, the EA/WR alone shows a significant negative relation, explaining respectively 9 and 13% of the variance in production. No significant correlation appeared during the fall season. (C) 2015 American Society of Civil Engineers.
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| 18. |
- Fazel, Nasim, et al.
(författare)
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Regionalization and spatial analysis of precipitation of the Urmia Lake Basin, Iran
- 2015
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Ingår i: World Environmental and Water Resources Congress 2015 : Floods, Droughts, and Ecosystems - Proceedings of the 2015 World Environmental and Water Resources Congress - Floods, Droughts, and Ecosystems - Proceedings of the 2015 World Environmental and Water Resources Congress. - Reston, VA : American Society of Civil Engineers. - 9780784479162 ; , s. 1101-1107
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Konferensbidrag (refereegranskat)abstract
- The spatial patterns of precipitation regarding physiography and atmospheric circulations in the Lake Urmia Basin have been investigated. Daily rainfall time series for the 50 most reliable precipitation stations for the period 1980-2010 were analyzed to detect the regional precipitation pattern. To identify rainfall homogeneous regions, principal component analysis was applied to the precipitation dataset. Agglomerative hierarchical clustering analysis using the Ward and Euclidean distance methods revealed three distinctive precipitation regions in the basin influenced by topography and lake. The first region (G1) covers the north and northeastern part of the Lake Urmia. G2 includes stations located in south and southeastern part of the basin, while G3 covers the western part of the lake basin. The results from this study can be used to better plan agricultural land use, cropping patterns and water management in the delineated homogeneous rainfall regions.
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| 19. |
- Fazel, Nasim, et al.
(författare)
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Regionalization of precipitation characteristics in Iran's Lake Urmia basin
- 2018
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Ingår i: Journal of Theoretical and Applied Climatology. - : Springer Science and Business Media LLC. - 0177-798X .- 1434-4483. ; 132:1-2, s. 363-373
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Tidskriftsartikel (refereegranskat)abstract
- Lake Urmia in northwest Iran, once one of the largest hypersaline lakes in the world, has shrunk by almost 90% in area and 80% in volume during the last four decades. To improve the understanding of regional differences in water availability throughout the region and to refine the existing information on precipitation variability, this study investigated the spatial pattern of precipitation for the Lake Urmia basin. Daily rainfall time series from 122 precipitation stations with different record lengths were used to extract 15 statistical descriptors comprising 25th percentile, 75th percentile, and coefficient of variation for annual and seasonal total precipitation. Principal component analysis in association with cluster analysis identified three main homogeneous precipitation groups in the lake basin. The first sub-region (group 1) includes stations located in the center and southeast; the second sub-region (group 2) covers mostly northern and northeastern part of the basin, and the third sub-region (group 3) covers the western and southern edges of the basin. Results of principal component (PC) and clustering analyses showed that seasonal precipitation variation is the most important feature controlling the spatial pattern of precipitation in the lake basin. The 25th and 75th percentiles of winter and autumn are the most important variables controlling the spatial pattern of the first rotated principal component explaining about 32% of the total variance. Summer and spring precipitation variations are the most important variables in the second and third rotated principal components, respectively. Seasonal variation in precipitation amount and seasonality are explained by topography and influenced by the lake and westerly winds that are related to the strength of the North Atlantic Oscillation. Despite using incomplete time series with different lengths, the identified sub-regions are physically meaningful.
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| 20. |
- Foster, Kean L., et al.
(författare)
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Seasonal streamflow forecast: a GCM multi-model downscaling approach
- 2010
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Ingår i: Hydrology Research. - : IWA Publishing. - 1998-9563 .- 0029-1277 .- 2224-7955. ; 41:6, s. 503-507
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Tidskriftsartikel (refereegranskat)abstract
- This work investigates the predictability of seasonal to inter-annual streamflow over several river basins in Norway through the use of multi-model ensembles. As general circulation models (GCMs) do not explicitly simulate streamflow, a statistical link is made between GCM-forecast fields generated in December and average streamflow in the melting season May-June. By using the Climate Predictability Tool (CPT) three models were constructed and from these a multi-model was built. The multi-model forecast is tested against climatology to determine the quality of the forecast. Results from the forecasts show that the multi-model performs better than the individual models and that this method shows improved forecast skills if compared to previous studies conducted in the same basins. The highest forecast skills are found for basins located in the southwest of Norway. The physical interpretation for this is that stations on the windward side of the Scandinavian mountains are exposed to the prevailing winds from the Atlantic Ocean, a principal source of predictive information from the atmosphere on this timescale.
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| 21. |
- Foster, Kean, et al.
(författare)
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The development and evaluation of a hydrological seasonal forecast system prototype for predicting spring flood volumes in Swedish rivers
- 2018
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Ingår i: Hydrology and Earth System Sciences. - : Copernicus GmbH. - 1027-5606 .- 1607-7938. ; 22:5, s. 2953-2970
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Tidskriftsartikel (refereegranskat)abstract
- Hydropower makes up nearly half of Sweden's electrical energy production. However, the distribution of the water resources is not aligned with demand, as most of the inflows to the reservoirs occur during the spring flood period. This means that carefully planned reservoir management is required to help redistribute water resources to ensure optimal production and accurate forecasts of the spring flood volume (SFV) is essential for this. The current operational SFV forecasts use a historical ensemble approach where the HBV model is forced with historical observations of precipitation and temperature. In this work we develop and test a multi-model prototype, building on previous work, and evaluate its ability to forecast the SFV in 84 sub-basins in northern Sweden. The hypothesis explored in this work is that a multi-model seasonal forecast system incorporating different modelling approaches is generally more skilful at forecasting the SFV in snow dominated regions than a forecast system that utilises only one approach. The testing is done using cross-validated hindcasts for the period 1981-2015 and the results are evaluated against both climatology and the current system to determine skill. Both the multi-model methods considered showed skill over the reference forecasts. The version that combined the historical modelling chain, dynamical modelling chain, and statistical modelling chain performed better than the other and was chosen for the prototype. The prototype was able to outperform the current operational system 57% of the time on average and reduce the error in the SFV by ∼ 6% across all sub-basins and forecast dates.
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| 22. |
- Fujita, Thais, et al.
(författare)
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Simulating Discharge in a Non-Dammed River of Southeastern South America Using SWAT Model
- 2022
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Ingår i: Water. - : MDPI AG. - 2073-4441. ; 14:3
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Tidskriftsartikel (refereegranskat)abstract
- Within a single region, it is possible to identify opposite changes in flow production. This proved to be the case for several basins in southeastern South America. It remains challenging to the causes this behavior and whether changes in streamflow will continue at current levels or decline in the coming decades. In this study, we used the Soil Water Assessment Tool to simulate monthly river discharge in the Ivaí River Basin, an unregulated medium-sized catchment and tributary of the Upper Paraná River Basin. After calibration, the simulated flow regime for the five streamflow stations based on the Nash-Sutcliffe Efficiency index (NSE) rated four of the streamflow stations Very Good (NSE between 0.86 and 0.89) and only one in the Good index (0.70). The overall flow behavior was well represented, although an underestimation was identified in four monitoring stations. Through assessment of its functionality and limitations in terms of specific flow duration curves percentages, the calibrated model could provide (to managers) the reliability needed for a realistic intervention. The results of this study may assist managers and support public policies for the use of water resources at the Ivaí River basin.
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| 23. |
- Gabitsinashvili, George, et al.
(författare)
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Evaluation of artificial neural network techniques for river flow forecasting
- 2007
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Ingår i: Environmental Engineering and Management Journal. - 1582-9596 .- 1843-3707. ; 6:1, s. 37-43
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Konferensbidrag (refereegranskat)abstract
- River runoff forecasting is one of the most complex areas of research in hydrology because of the uncertainty of hydrological and meteorological parameters and scarcity of adequate records. Artificial neural networks (ANN) can be an efficient way of modeling stream flow processes as it is capable of controlling and modelling nonlinear and complex systems and does not require describing the complex nature of the hydrological processes. In this study, daily river flow is forecasted using two ANN models: a Multi Layer Perceptron (MLP) network and a Radial Basis Function (RBF) Network. The ANN technique was applied to predict runoff in three mountain rivers in Georgia. The results show that ANNs can be successfully applied to forecast runoff using rainfall time series for the studied sub-catchments. A comparative study of both networks indicates that RBF models require little background knowledge of ANNs and need less time for development.
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| 24. |
- Georgiadou, Elisavet, et al.
(författare)
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Bomb-pulse (14)C analysis combined with (13)C and (15)N measurements in blood serum from residents of Malmö, Sweden.
- 2013
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Ingår i: Radiation and Environmental Biophysics. - : Springer Science and Business Media LLC. - 1432-2099 .- 0301-634X. ; 52:2, s. 175-187
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Forskningsöversikt (refereegranskat)abstract
- The (14)C content of 60 human blood serum samples from residents of Malmö (Sweden) in 1978, obtained from a biobank, has been measured to estimate the accuracy of (14)C bomb-pulse dating. The difference between the date estimated using the Calibomb software and sampling date varied between -3 ± 0.4 and +0.2 ± 0.5 years. The average age deviation of all samples was -1.5 ± 0.7 years, with the delay between production and consumption of foodstuffs being probably the dominating cause. The potential influence of food habits on the (14)C date has been evaluated using stable isotope δ(13)C and δ(15)N analysis and information about the dietary habits of the investigated individuals. Although the group consisting of lacto-ovo vegetarians and vegans (pooled group) was not completely separated from the omnivores in a stable isotopic trophic level diagram, this analysis proved to add valuable information on probable dietary habits. The age deviation of the sampling date from the respective Calibomb date was found strongly correlated with the δ(13)C values, probably due to influence from marine diet components. For the omnivore individuals, there were indications of seasonal effects on δ(13)C and the age deviation. No significant correlation was found between the age deviation and the δ(15)N values of any dietary group. No influence of sex or year of birth was found on neither the (14)C nor the δ(13)C and δ(15)N values of the serum samples. The data were also divided into two groups (omnivores and pooled group), based on the level of δ(15)N in the samples. The consumption of high δ(15)N-valued fish and birds can be responsible for this clustering.
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| 25. |
- Georgiadou, Elisavet, et al.
(författare)
-
Bomb-pulse 14C analysis combined with 13C and 15N measurements in blood serum from residents of Malmö, Sweden
- 2013
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Konferensbidrag (refereegranskat)abstract
- The 14C content of 60 human blood serum samples from residents of Malmö (Sweden) in 1978, obtained from a biobank, has been measured to estimate the accuracy of 14C bomb-pulse dating. The difference between the date estimated by using the Calibomb software and sampling date varied between -3±0.4 and +0.2±0.5 years. The average age deviation of all samples was -1.5±0.7 years, with the delay between production and consumption of foodstuffs being probably the dominating cause. The potential influence of food habits on the 14C date has been evaluated using stable isotope δ13C and δ15N analysis and information about the dietary habits of the investigated individuals. Although the group consisting of lacto-ovo vegetarians and vegans (pooled group) was not completely separated from the omnivores in a stable isotopic trophic level diagram, this analysis proved to add valuable information on probable dietary habits. The age deviation of the sampling date from the respective Calibomb date was found strongly correlated with the δ13C values, probably due to influence from marine diet components. For the omnivore individuals, there were indications of seasonal effects on δ13C and the age deviation. No significant correlation was found between the age deviation and the δ15N values of any dietary group. No influence of sex or year of birth was found on neither the 14C nor the δ13C and δ15N values of the serum samples. The data were also divided into two groups (omnivores and pooled group), based on the level of δ15N in the samples. The consumption of high δ15N-valued fish and birds can be responsible for this clustering.
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| 26. |
- Georgiadou, Elisavet, et al.
(författare)
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Potential Influence of Diet on Bomb-Pulse Dating of Human Plaque Samples
- 2013
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Ingår i: Radiocarbon. - : Cambridge University Press (CUP). - 0033-8222. ; 55:2-3, s. 874-884
-
Tidskriftsartikel (refereegranskat)abstract
- The radiocarbon concentration of different atherosclerotic plaque fragments obtained from 20 patients in Portugal, operated in 2000-2001, has been measured in order to define the year of plaque formation. A difference of 1.8-15 yr was observed, with the mean and median both 9 yr, between the bomb-pulse date estimated with the CALIBomb software and the operation date. Stable isotope (delta C-13 and delta N-15) analysis was also performed and provides insight to the diet of the subjects. The wide range of measured stable isotope values could indicate that the subjects' diet varied, including an abundance of marine foodstuffs. It could also mean a different isotope fractionation process for the different plaque fragments (cap, core, interface to media) and a possible difference in tissues in which the various fragments are formed. Analysis of delta C-13 and delta N-15 values of each patient separately revealed subjects considered more influenced by marine foodstuffs consumption.
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| 27. |
- Guegan, Marion, et al.
(författare)
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Developing a module for estimating climate warming effects on hydropower pricing in California
- 2012
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Ingår i: Energy Policy. - : Elsevier BV. - 1873-6777 .- 0301-4215. ; 42, s. 261-271
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Tidskriftsartikel (refereegranskat)abstract
- Climate warming is expected to alter hydropower generation in California through affecting the annual stream-flow regimes and reducing snowpack. On the other hand, increased temperatures are expected to increase hydropower demand for cooling in warm periods while decreasing demand for heating in winter, subsequently altering the annual hydropower pricing patterns. The resulting variations in hydropower supply and pricing regimes necessitate changes in reservoir operations to minimize the revenue losses from climate warming. Previous studies in California have only explored the effects of hydrological changes on hydropower generation and revenues. This study builds a long-term hydropower pricing estimation tool, based on artificial neural network (ANN), to develop pricing scenarios under different climate warming scenarios. Results suggest higher average hydropower prices under climate warming scenarios than under historical climate. The developed tool is integrated with California's Energy-Based Hydropower Optimization Model (EBHOM) to facilitate simultaneous consideration of climate warming on hydropower supply, demand and pricing. EBHOM estimates an additional 5% drop in annual revenues under a dry warming scenario when climate change impacts on pricing are considered, with respect to when such effects are ignored, underlining the importance of considering changes in hydropower demand and pricing in future studies and policy making. (C) 2011 Elsevier Ltd. All rights reserved.
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| 28. |
- Hashemi, Hossein, et al.
(författare)
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An extended modeling approach to assess climate change impacts on groundwater recharge and adaptation in arid areas
- 2014
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Ingår i: Hydrology and Earth System Sciences Discussions. - : Copernicus GmbH. - 1812-2108. ; 11:10, s. 11797-11835
-
Tidskriftsartikel (populärvet., debatt m.m.)abstract
- The impact of future climate scenarios on surface and groundwater resources was simulated using a modeling approach for an artificial recharge area in arid southern Iran. Future climate data for the periods of 2010–2030 and 2030–2050 were acquired from the Canadian Global Coupled Model (CGCM 3.1) for scenarios A1B, A2, and B1. These scenarios were adapted to the studied region using the delta-change method. The modified version of the HBV model (Qbox) was used to simulate runoff in a flash flood prone catchment. The model was calibrated and validated for the period 2002– 2011 using daily discharge data. The projected climate variables were used to simulate future runoff. The rainfall–runoff model was then coupled to a calibrated groundwater flow and recharge model (MODFLOW) to simulate future recharge and groundwater hydraulic head. The results of the rainfall–runoff modeling showed that under the B1 scenario the number of floods might increase in the area. This in turn calls for a proper management, as this is the only source of fresh water supply in the studied region. The results of the groundwater recharge modeling showed no significant difference be- tween present and future recharge for all scenarios. Owing to that, four abstraction and recharge scenarios were assumed to simulate the groundwater level and recharged water in the studied aquifer. The results showed that the abstraction scenarios have the most substantial effect on the groundwater level and the continuation of current pumping rate would lead to a groundwater decline by 18 m up to 2050.
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| 29. |
- Hashemi, Hossein, et al.
(författare)
-
Coupled modeling approach to assess climate change impacts on groundwater recharge and adaptation in arid areas : Coupled modeling approach to assess climate change impacts on groundwater recharge
- 2015
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Ingår i: Hydrology and Earth System Sciences. - : Copernicus GmbH. - 1607-7938. ; 19:10, s. 4165-4181
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of future climate scenarios on surface and groundwater resources was simulated using a model- ing approach for an artificial recharge area in arid southern Iran. Future climate data for the periods of 2010–2030 and 2030–2050 were acquired from the Canadian Global Coupled Model (CGCM 3.1) for scenarios A1B, A2, and B1. These scenarios were adapted to the studied region us- ing the delta-change method. A conceptual rainfall–runoff model (Qbox) was used to simulate runoff in a flash flood prone catchment. The model was calibrated and validated for the period 2002–2011 using daily discharge data. The projected climate variables were used to simulate future runoff. The rainfall–runoff model was then coupled to a calibrated groundwater flow and recharge model (MODFLOW) to simulate future recharge and groundwater hydraulic heads. As a result of the rainfall–runoff modeling, under the B1 scenario the number of floods is projected to slightly increase in the area. This in turn calls for proper management, as this is the only source of fresh water supply in the studied region. The results of the groundwater recharge modeling showed no significant difference between present and future recharge for all scenarios. Owing to that, four abstraction and recharge scenarios were assumed to simulate the groundwater level and recharge amount in the studied aquifer. The results showed that the abstraction scenarios have the most substantial effect on the groundwater level and the continuation of current pumping rate would lead to a groundwater decline by 18 m up to 2050.
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| 30. |
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| 31. |
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| 32. |
- Jebari, Sihem, et al.
(författare)
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Regionalizing short-term rainfall affected by topography in semiarid Tunisia
- 2007
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Ingår i: Hydrological Sciences Journal. - : Informa UK Limited. - 0262-6667 .- 2150-3435. ; 52:6, s. 1199-1215
-
Tidskriftsartikel (refereegranskat)abstract
- The characteristics of fine time-scale rainfall are important in many hydrological applications, such as infiltration, erosion and flooding. The spatial properties of such rainfall are, however, seldom known, especially for arid and semi-arid areas. A better knowledge of fine time-scale rainfall and also comparison with daily rainfall may yield possibilities for disaggregation. For this purpose, rainfall data of different time scales, from 1-min to daily, from 25 stations during four years (1995–1998), were spatially analysed by means of spatial correlation, empirical orthogonal function (EOF) and hierarchical clustering. The results show that the spatial correlation is typically non-isotropic and varying, depending on topography and local meteorological settings. Similarly, spatial patterns of EOF are closely related to main atmospheric synoptic situations as influenced by orography and spatial dependence regarding areas with predominant convective and frontal rainfall. The clustering displayed different homogeneous sub-groups over the Tunisian Dorsal Mountains that can be used to better manage the limited water resources that often depend on fine time-scale rainfall variability.
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| 33. |
- Jonsdottir, Jona Finndis, et al.
(författare)
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Filling gaps in measured discharge series with model-generated series
- 2008
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Ingår i: Journal of Hydrologic Engineering. - 1084-0699. ; 13:9, s. 905-909
-
Tidskriftsartikel (refereegranskat)abstract
- Abstract in UndeterminedGaps in measured discharge series are common in Iceland, especially during winter, but reconstructed series are needed for a number of applications. Modeled series are therefore sometimes used to fill the gaps to create a continuous series, but the modeled inserts may have different statistical characteristics from the observed series, whilst their initial and final values rarely coincide with the corresponding measured values. Where gaps are numerous, individual treatment of each gap is time-consuming and often impractical. A method for adjusting modeled sequences to be inserted into gaps was therefore designed with the objective of reducing the difference between model-generated inserts and recorded series. This paper reports on the performance of the method and shows how an improved fit can be attained by adjusting the model-generated inserts so as to smoothly match the discharges observed before and after a gap.
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| 34. |
- Jonsdottir, Jona Finndis, et al.
(författare)
-
Long-term variability in precipitation and streamfiow in Iceland and relations to atmospheric circulation
- 2009
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Ingår i: International Journal of Climatology. - : Wiley. - 1097-0088 .- 0899-8418. ; 29:10, s. 1369-1380
-
Tidskriftsartikel (refereegranskat)abstract
- How the variability of the atmospheric circulation affects precipitation in Iceland is not completely understood. Also, the sea surface temperature (SST) has a strong influence on the temperature over the country, and thereby, snow and glacial melt. This study, therefore, aims at explaining how atmospheric circulation and sea surface temperature influence seasonal and annual precipitation, and, consequently, runoff in Iceland. Empirical orthogonal function (EOF) analysis is performed on annual and seasonal time series of precipitation and discharge to identify their key modes of variability during the period 1966-2004. The correlation between the time series of each EOF mode with individual time series of sea level pressure (SLP), air temperature and SST was then evaluated. The analyses evidenced how large-scale climate variables are connected to the regional precipitation and runoff in Iceland. They showed that the strength of the polar vortex may be, at least, as important for the precipitation in some areas of Iceland as the strength of the Icelandic Low (IL). Moreover, the location of the semi-permanent IL often defines the predominant wind direction over the country and, as such, the regions of preferred precipitation. Since the watersheds act as large precipitation gauges with response patterns depending on the geology and glaciers, the variability of the annual discharge closely resembles the variability of precipitation, except for the glacial rivers. Glacial melt is highly correlated to air temperature and SST, and the spring discharge is affected by winter and spring temperatures. The results also revealed that Icelandic hydrological conditions in the spring can be forecasted by precipitation and temperature of the autumn and winter seasons, as well as by the general prevalent circulation patterns. Additionally, a potential for seasonal forecast of precipitation, and river discharge in other seasons was identified, particularly if seasonal forecast of SLP is available. Copyright (C) 2008 Royal Meteorological Society
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| 35. |
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| 36. |
- Jonsdottir, Jona Finndis, et al.
(författare)
-
Trend analysis in Icelandic discharge, temperature and precipitation series by parametric methods
- 2008
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Ingår i: Hydrology Research. - : IWA Publishing. - 1998-9563 .- 0029-1277 .- 2224-7955. ; 39:5-6, s. 425-436
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents results of analyses by parametric methods of annual means of temperature, precipitation and discharge, and of seasonal maximum precipitation at 17, 28 and 10 Icelandic stations, respectively, for the period 1961-2000. Trends in mean seasonal temperature and precipitation are in broad agreement with results found by other authors using other methods. A positive trend appears in both mean annual temperature and mean temperatures in most seasons. Annual mean precipitation trends are positive in most seasons except for negative trends in the September-November season in the south. Additionally, positive trends appear in maximum one-, three- and five-day precipitation, both during the spring and autumn, except at a group of stations in central Iceland. Some of the positive trends in mean annual and seasonal precipitation may, however, be attributed to the positive trend in temperature which may have influenced gauge catch. Trends in mean annual and seasonal discharge are small and statistically insignificant; the trends found in temperature and precipitation do not all relate directly to trends in discharge but suggest hypotheses for further study of the relationships between them.
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| 37. |
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| 38. |
- Jonsdottir, Jona Finndis, et al.
(författare)
-
Trend analysis of Icelandic discharge, precipitation and temperature series.
- 2006
-
Ingår i: Nordic Hydrology. - : IWA Publishing. - 0029-1277. ; 37:4-5, s. 365-376
-
Tidskriftsartikel (refereegranskat)abstract
- This study is a part of a Nordic co-operative research project, Climate and Energy, funded by Nordic Energy Research and the Nordic energy sector. The project has the objective of a comprehensive assessment of the impact of climate change on Nordic renewable energy resources including hydropower, wind power, biofuels and solar energy. In this paper, the long term variability of precipitation, temperature and discharge of Icelandic rivers is analyzed with respect to trends. Trend is tested for two periods: 1941–2002, since the longest Icelandic discharge records reach 60 years back in time, and 1961–2000, so that a larger set of discharge records could be included, as only a few Icelandic discharge records extend more than 40 years back in time. An eventual trend in the time series is analyzed using the Mann–Kendall test. The test is applied to the time series of both annual and seasonal values, and also to the timing and volume of the maximum daily discharge in spring and autumn, respectively. The main conclusions from the study are that, despite significant increase in measured precipitation, discharge in non-glacial rivers has not increased. Meanwhile, spring temperatures have a negative trend and spring floods, therefore, are larger and delayed.
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| 39. |
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| 40. |
- Klove, Bjorn, et al.
(författare)
-
Climate change impacts on groundwater and dependent ecosystems
- 2014
-
Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694. ; 518, s. 250-266
-
Tidskriftsartikel (refereegranskat)abstract
- Aquifers and groundwater-dependent ecosystems (GDEs) are facing increasing pressure from water consumption, irrigation and climate change. These pressures modify groundwater levels and their temporal patterns and threaten vital ecosystem services such as arable land irrigation and ecosystem water requirements, especially during droughts. This review examines climate change effects on groundwater and dependent ecosystems. The mechanisms affecting natural variability in the global climate and the consequences of climate and land use changes due to anthropogenic influences are summarised based on studies from different hydrogeological strata and climate zones. The impacts on ecosystems are discussed based on current findings on factors influencing the biodiversity and functioning of aquatic and terrestrial ecosystems. The influence of changes to groundwater on GDE biodiversity and future threats posed by climate change is reviewed, using information mainly from surface water studies and knowledge of aquifer and groundwater ecosystems. Several gaps in research are identified. Due to lack of understanding of several key processes, the uncertainty associated with management techniques such as numerical modelling is high. The possibilities and roles of new methodologies such as indicators and modelling methods are discussed in the context of integrated groundwater resources management. Examples are provided of management impacts on groundwater, with recommendations on sustainable management of groundwater. (C) 2013 Elsevier B.V. All rights reserved.
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| 41. |
- Madani, Kaveh, et al.
(författare)
-
Climate change impacts on high-elevation hydroelectricity in California
- 2014
-
Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694. ; 510, s. 153-163
-
Tidskriftsartikel (refereegranskat)abstract
- While only about 30% of California's usable water storage capacity lies at higher elevations, high-elevation (above 300 m) hydropower units generate, on average, 74% of California's in-state hydroelectricity. In general, high-elevation plants have small man-made reservoirs and rely mainly on snowpack. Their low built-in storage capacity is a concern with regard to climate warming. Snowmelt is expected to shift to earlier in the year, and the system may not be able to store sufficient water for release in high-demand periods. Previous studies have explored the climate warming effects on California's high-elevation hydropower by focusing on the supply side (exploring the effects of hydrological changes on generation and revenues) ignoring the warming effects on hydroelectricity demand and pricing. This study extends the previous work by simultaneous consideration of climate change effects on high-elevation hydropower supply and pricing in California. The California's Energy-Based Hydropower Optimization Model (EBHOM 2.0) is applied to evaluate the adaptability of California's high-elevation hydropower system to climate warming, considering the warming effects on hydroelectricity supply and pricing. The model's results relative to energy generation, energy spills, reservoir energy storage, and average shadow prices of energy generation and storage capacity expansion are examined and discussed. These results are compared with previous studies to emphasize the need to consider climate change effects on hydroelectricity demand and pricing when exploring the effects of climate change on hydropower operations. (C) 2013 Elsevier B.V. All rights reserved.
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| 42. |
- Malekmohammadi, Bahram, et al.
(författare)
-
Environmental Risk Assessment of Wetland Ecosystems Using Bayesian Belief Networks
- 2023
-
Ingår i: Hydrology. - : MDPI AG. - 2306-5338. ; 10:1
-
Tidskriftsartikel (refereegranskat)abstract
- Wetlands are valuable natural capital and sensitive ecosystems facing significant risks from anthropogenic and climatic stressors. An assessment of the environmental risk levels for wetlands’ dynamic ecosystems can provide a better understanding of their current ecosystem health and functions. Different levels of environmental risk are defined by considering the categories of risk and the probability and severity of each in the environment. Determining environmental risk levels provides a general overview of ecosystem function. This mechanism increases the visibility of risk levels and their values in three distinct states (i.e., low, moderate, and high) associated with ecosystem function. The Bayesian belief network (BBN) is a novel tool for determining environmental risk levels and monitoring the effectiveness of environmental planning and management measures in reducing the levels of risk. This study develops a robust methodological framework for determining the overall level of risks based on a combination of varied environmental risk factors using the BBN model. The proposed model is adopted for a case study of Shadegan International Wetlands (SIWs), which consist of a series of Ramsar wetlands in the southwest of Iran with international ecological significance. A comprehensive list of parameters and variables contributing to the environmental risk for the wetlands and their relationships were identified through a review of literature and expert judgment to develop an influence diagram. The BBN model is adopted for the case study location by determining the states of variables in the network and filling the probability distribution tables. The environmental risk levels for the SIWs are determined based on the results obtained at the output node of the BBN. A sensitivity analysis is performed for the BBN model. We proposed model-informed management strategies for wetland risk control. According to the BBN model results, the SIWs ecosystems are under threat from a high level of environmental risk. Prolonged drought has been identified as the primary contributor to the SIWs’ environmental risk levels.
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| 43. |
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| 44. |
- Nguyen, Tinh Dang, et al.
(författare)
-
Relationship between tropical Pacific and Indian Ocean sea surface temperature and monthly precipitation over the central highland, Vietnam
- 2007
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Ingår i: International Journal of Climatology. - : Wiley. - 1097-0088 .- 0899-8418. ; 27:11, s. 1439-1454
-
Tidskriftsartikel (refereegranskat)abstract
- The relationship between monthly sea-surface temperature (SST) in the tropical Pacific and the Indian Ocean and monthly precipitation over the Vietnamese central highlands (VCH) has been investigated by means of singular value decomposition. The seasonal variation of SST plays a critical role in the onset of the monsoon season and convective rain band movement in the inter-tropical convergence zone. The relationships between precipitation and SST in both oceans vary significantly through the rainy season. In April, ENSO is strongly correlated with precipitation over the VCH, while the Indian Ocean SST only shows a significant correlation with precipitation in the northern VCH. In May, there is no significant relationship between precipitation and SST in either of the oceans. In June, precipitation over the VCH is negatively correlated with the northern Indian Ocean and the southern Pacific SST. Through July to September, no significant relationships were found between the Indian Ocean SST and precipitation patterns. The equatorial central to the eastern Pacific SST, in turn, is positively correlated with precipitation in a small area from the north to the south of the VCH. In October, precipitation over the VCH is strongly related to ENSO and positively correlated with the equatorial eastern Indian Ocean SST. For November, the north-western Pacific as well as the equatorial eastern Indian Ocean SST is positively and strongly correlated with precipitation over the VCH. Lag-time analyses demonstrate a potential link between the Pacific SST and monthly precipitation patterns through the rainy season from one to three months in advance, and between the Indian Ocean SST and monthly precipitation patterns in October and November from one to two months in advance. The analysed results provide a strong basis for a predictive scheme, but further analysis of skill levels needs to be developed. Copyright © 2007 Royal Meteorological Society
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| 45. |
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| 46. |
- Nilsson, Andreas, et al.
(författare)
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Holocene geocentric dipole tilt model constrained by sedimentary paleomagnetic data
- 2010
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Ingår i: Geochemistry Geophysics Geosystems. - 1525-2027. ; 11, s. 08018-08018
-
Tidskriftsartikel (refereegranskat)abstract
- Paleomagnetic data, although undeniably limited, have been used to constrain complex time-varying geomagnetic field models. Here we present four different versions of a time varying geocentric dipole model for the past approximately 9000 years based on a limited selection of sedimentary paleomagnetic data with good spatial coverage. The robustness of the modeling approach is evaluated using modern magnetic observation station data provided by the World Data Centre for Geomagnetism in Edinburgh and we discuss the magnitude of the error introduced by insufficient data coverage. The prediction in terms of directional variations is tested against paleomagnetic data from 63 different sedimentary sites and compared to results from recently published spherical harmonic geomagnetic field models. We find that the dipole estimate can explain the paleomagnetic data almost as well as the more complicated spherical harmonic models. Specific areas and records are identified where there are significant differences between the performance of the dipole estimate and the spherical harmonic models. Our results suggest that many of the differences between the dipole model predictions and the paleomagnetic data can be related to poor paleomagnetic quality and/or the lack of accurate and precise time control inherent to some of the records. These results agree with Valet et al. ( 2008) who suggested that the CALS7K. 2 model probably underestimates the dipole contribution in order to reduce the misfit between the inversion and the data. We conclude that better paleomagnetic data and associated time control are needed to improve global geomagnetic field models.
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| 47. |
- Nilsson, Erik, et al.
(författare)
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Drivers of abrupt and gradual changes in agricultural systems in Chad
- 2020
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Ingår i: Regional Environmental Change. - : Springer Science and Business Media LLC. - 1436-3798 .- 1436-378X. ; 20
-
Tidskriftsartikel (refereegranskat)abstract
- The countries in the Sahel are undergoing rapid changes due to a mixture of demographic, ecological, and economic transformations. Rural livelihoods in these countries are predominantly engaged in agriculture, which is a foundational component of both food security and the general economy. The relationships between ongoing socio-economic transformation and the agricultural sector are clearly important to address poverty and sustainable development, but have received little academic attention on a subnational level of analysis. This paper addresses this by bringing together new datasets on demography, international aid, food security reports, and soil moisture to analyze the drivers of change in the agricultural sector on a subnational level in Chad. Both regression analyses and qualitative methods based on descriptions in food security reports are used to evaluate the relationships between these datasets to agricultural statistics for the period 1990–2016. It finds that changes to crop water availability from rainfall largely are decoupled from the long-term increases in crop production. On the other hand, it shows that population changes and international aid can explain differences in long-term agricultural changes between Chad’s regions. Moreover, stochastic factors such as farm support programs, market prices, access to new markets, and accommodation of refugees are identified as important to grasp abrupt changes in the crop production. Beyond the specific findings for Chad, this study presents a framework for improved evaluation of the drivers behind subnational crop production on multi-annual and decadal time scales, with broad applicability to agricultural systems in the Sahel.
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| 48. |
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| 49. |
- Nilsson, Erik, et al.
(författare)
-
Hydro-climatic variability and agricultural production on the shores of Lake Chad
- 2016
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Ingår i: Environmental Development. - : Elsevier BV. - 2211-4645. ; 20, s. 15-30
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of this study is to present and analyze previously unpublished quantitative agricultural data for the area on the shores of Lake Chad in Chad, and explore its relations to hydro-climatic factors (lake levels, rainfall and temperature). This is a rural area with livelihoods based on agropastoral and fishing activities, which are directly dependent on the region's high-varying hydro-climate. By using regression analysis on data from 1988 to 2012 this study was able to establish correlations between the latter and agricultural output. These correlations were used to build multivariate models to explore the predictive capacities of hydro-climatic factors with regards to the agricultural data. The selected models were able to account for considerable proportions of the agricultural dynamics. Some 5 of the 10 multivariate models tested had cross-validated R2s of 0.50 or more. Thus, there were still noteworthy unexplained variations in the agricultural data, which likely stem from technological, behavioral, economic and pest factors that were not explored in this study due do data limitations. Additional studies are called for to build on results presented here and further examine these relationships.
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| 50. |
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