| 1. |
- Abdallah, Mohammed, et al.
(författare)
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Reference evapotranspiration estimation in hyper-arid regions via D-vine copula based-quantile regression and comparison with empirical approaches and machine learning models
- 2022
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Ingår i: Journal of Hydrology: Regional Studies. - : Elsevier BV. - 2214-5818. ; 44
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Tidskriftsartikel (refereegranskat)abstract
- Study region: Two hyper-arid regions (Atbara and Kassala stations) in Sudan. Study focus: The study aims to evaluate the potential of the D-vine Copula-based quantile regression (DVQR) model for estimating daily ETo during 2000–2015 based on various input structures. Further, the DVQR model was compared with Multivariate Linear quantile regression (MLQR), Bayesians Model Averaging quantile regression (BMAQR), Empirical Models (EMMs), and Classical Machine Learning (CML). Besides, the CML models including Random Forest (RF), Support Vector Machine (SVM), Extreme Learning Machine (ELM), Extreme Gradient Boosting (XGBoost), and M5 Model Tree (M5Tree) were employed. New hydrological insights for the region: The original EMMs showed poor performance, which improved after calibration techniques. The DVQR, MLQR, and BMAQR models showed better performance than the calibrated EMMs. However, the DVQR model exhibited the highest accuracy than the MLQR and BMAQR models over two study sites. The M5Tree, SVM, and XGBoost models perfumed better than ELM and RF models at both study sites. The DVQR and XGBoost models showed equivalent performance (R2, NSE, and WIA > 0.99, MAE, and RMSE < 0.2) to the M5Tree and SVM models, but they had significantly more accuracy than the calibrated EMMs, MLQR, BMAQR, ELM, and RF models in two hyper-arid regions. Overall, the high dimensional DVQR model is recommended as a promising alternative technique for estimating daily ETo in hyper-arid climate conditions around the world.
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| 2. |
- Aminjafari, Saeid, et al.
(författare)
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Drivers and extent of surface water occurrence in the Selenga River Delta, Russia
- 2021
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Ingår i: Journal of Hydrology. - : Elsevier BV. - 2214-5818. ; 38
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Tidskriftsartikel (refereegranskat)abstract
- Study region: Selenga River Delta (SRD), Russia.Study focus: How is water occurrence changing in the SRD, and what are the hydroclimatic drivers behind these changes? The presence of water on the surface in river deltas is governed by land use, geomorphology, and the flux of water to and from the Delta. We trained an accurate image classification of the Landsat satellite imagery during the last 33 years to quantify surface water occurrence and its changes in the SRD. After comparing our estimations with global-scale data sets, we determined the hydrological drivers of these changes.New hydrological insights for the region: We find mild decreases in water occurrence in 51% of the SRD's surface area from 1987-2002 to 2003-2020. Water occurrence in the most affected areas decreased by 20% and in the most water-gaining areas increased by 10%. We find a significant relationship between water occurrence and runoff (R-2 = 0.56) that does not exist between water occurrence and suspended sediment concentration (SSC), Lake Baikal's water level, and potential evapotranspiration. The time series of water occurrence follows the peaks in the runoff but not its long-term trend. However, the extremes in SSC do not influence surface water occurrence (R-2 < 0.1), although their long-term trends are similar. Contrary to expected, we find that the Delta has a relatively stable long-term water availability for the time being.
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| 3. |
- Asokan, Shilpa M., et al.
(författare)
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Climate model performance and change projection for freshwater fluxes : comparison for irrigated areas in Central and South Asia
- 2016
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Ingår i: Journal of Hydrology. - : Elsevier BV. - 2214-5818. ; 5, s. 48-65
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Tidskriftsartikel (refereegranskat)abstract
- Study region: The large semi-arid Aral Region in Central Asia and the smaller tropical Mahanadi River Basin (MRB) in India. Study focus: Few studies have so far evaluated the performance of the latest generation ofglobal climate models on hydrological basin scales. We here investigate the performanceand projections of the global climate models in the Coupled Model Intercomparison Project, Phase 5 (CMIP5) for freshwater fluxes and their changes in two regional hydrological basins, which are both irrigated but of different scale and with different climate. New hydrological insights for the region: For precipitation in both regions, model accuracy relative to observations has remained the same or decreased in successive climate model generations until and including CMIP5. No single climate model out-performs other models across all key freshwater variables in any of the investigated basins. Scale effects are not evident from global model application directly to freshwater assessment for the two basins of widely different size. Overall, model results are less accurate and more uncertain for freshwater fluxes than for temperature, and particularly so for model-implied water storage changes. Also, the monsoon-driven runoff seasonality in MRB is not accurately reproduced. Model projections agree on evapotranspiration increase in both regions until the climatic period 2070–2099. This increase is fed by precipitation increase in MRB and by runoff water (thereby decreasing runoff) in the Aral Region.
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| 4. |
- Breinl, Korbinian, et al.
(författare)
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Space-time disaggregation of precipitation and temperature across different climates and spatial scales
- 2019
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Ingår i: Journal of Hydrology. - : ELSEVIER SCIENCE BV. - 2214-5818. ; 21, s. 126-146
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Tidskriftsartikel (refereegranskat)abstract
- Study region: This study focuses on two study areas: the Province of Trento (Italy; 6200 km(2)), and entire Sweden (447000km(2)). The Province of Trento is a complex mountainous area including subarctic, humid continental and Tundra climates. Sweden, instead, is mainly dominated by a subarctic climate in the North and an oceanic climate in the South. Study focus: Hydrological predictions often require long weather time series of high temporal resolution. Daily observations typically exceed the length of sub-daily observations, and daily gauges are more widely available than sub-daily gauges. The issue can be overcome by disaggregating daily into sub-daily values. We present an open-source tool for the non-parametric space-time disaggregation of daily precipitation and temperature into hourly values called spatial method of fragments (S-MOF). A large number of comparative experiments was conducted for both S-MOF and MOF in the two study regions. New hydrological insights for the region: Our experiments demonstrate the applicability of the univariate and spatial method of fragments in the two temperate/subarctic study regions where snow processes are important. S-MOF is able to produce consistent precipitation and temperature fields at sub-daily resolution with acceptable method related bias. For precipitation, although climatologically more complex, S-MOF generally leads to better results in the Province of Trento than in Sweden, mainly due to the smaller spatial extent of the former region.
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| 5. |
- Capell, Rene, et al.
(författare)
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From local measures to regional impacts : Modelling changes in nutrient loads to the Baltic Sea
- 2021
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Ingår i: Journal of Hydrology. - : Elsevier. - 2214-5818. ; 36
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Tidskriftsartikel (refereegranskat)abstract
- Study Region: Our study region is the Baltic Sea Drainage Basin (BSDB), which covers an area of 1.8 Mio km2 distributed over 14 countries in northern Europe. Study Focus: We use a large-scale hydrological and nutrient transport model (E-HYPE) to model basin-wide impacts of measure scenarios on the Baltic Sea, where eutrophication is a critical issue for the marine ecosystem. We constructed measure scenarios based on stakeholder acceptance, established in workshops in different regions around the Baltic. These measures include local stream reach to catchment scale measures aiming to reduce nutrient transport into the stream network (buffer strips, stormwater ponds) and measures aiming to reduce regional nutrient source releases (fertiliser leaching rates, rural household emissions). New Hydrological Insights for the Region: Nutrient load reductions are often needed to reduce eutrophication and improve overall surface water quality in fresh-water and enclosed bays and seas, where dilution is limited and load emissions have long residence times. To reduce riverine nutrient loads, remediation measures are necessary, e.g. establishment of buffer strips or improved wastewater treatment. Such measures are, however, typically not designed to target nutrient load reductions at sea outlets, but rather focus on local improvements. Here, we show that measures, notwithstanding other meliorating ecosystem benefits, must include reductions in load emissions across large basin areas to impact integrated net loads into coastal sea basins, because reduction measures that only target nutrient delivery to the stream network typically cannot be implemented in a significant enough proportion of the total drainage area of large coastal river basins. Our impact scenarios show BSDB-wide nutrient reductions of up to 9 % for nitrogen and phosphorus compared to a reference scenario, if load emissions are reduced in the scenario assumptions.
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| 6. |
- Cuartas, Luz Adriana, et al.
(författare)
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Hydrometeorological drought analysis through Two-variate Standardized Index for the Paraná River Basin, Brazil
- 2024
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Ingår i: Journal of Hydrology: Regional Studies. - 2214-5818. ; 54
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Tidskriftsartikel (refereegranskat)abstract
- Brazil has faced severe droughts in recent decades, significantly affecting agriculture, water supply, and hydropower generation, among other sectors. The Paraná River Basin, a major hub for hydropower, has been particularly affected, posing challenges for water management. To address this, we conducted a study to provide tailored climate information for the Brazilian hydroelectric sector. Given the complexity of hydrometeorological processes, involving hydrological, meteorological and climatological processes and anthropogenic factors, a multivariate approach is essential for drought assessment. We assessed the effectiveness of a Two-variate Standardized Index (TSI) in characterizing hydrometeorological droughts on large-scales basins and its potential as an operational decision support index. The TSI was compared with the Standardized Precipitation Index and the Standardized Streamflow Index, and we examined the correlation between TSI and Terrestrial Water Storage from GRACE and reservoir volumes, at different time scales. We used the HAND model and water table depth to gain a comprehensive understanding of drought conditions. The results show that the TSI outperforms the univariate indices SPI and SSFI in characterizing drought events in terms of severity and duration. The correlation analysis showed that time scales of 12 and 24 months are the most suitable for hydrometeorological drought monitoring. Overall, the study highlights the potential of TSI as an operational index for monitoring drought conditions and can be applied in basins with different climate regimes.
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| 7. |
- Derouiche, Sabrine, et al.
(författare)
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Characterisation of rainfall events in northern Tunisia using self-organising maps
- 2022
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Ingår i: Journal of Hydrology. - : Elsevier BV. - 2214-5818. ; 42
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Tidskriftsartikel (refereegranskat)abstract
- Study region: The study is carried out for northern Tunisia.Study focus: Precipitations are often analysed via intensity or accumulation for a specified timescale (e.g., annual, seasonal, etc). We propose in this study to analyse regional rainfall variability by adopting a variable time step through the rain event concept. This event-based approach, ensures the integration of information related to rain intermittency, which is one of the fundamental properties of precipitations. This study focuses essentially on wet spells characteristics derived from the aggregation of daily winter dataset over a 50 years period (1960–2009). The multivariate analysis, based on the combination of two clustering approaches, i.e., self-organizing map and hierarchical clustering, allows the identification of different rainfall regimes. This study helps to understand rainfall variability patterns and to address rainfall regionalization and water use management issues.New hydrological insights for the region: The winter precipitations of northern Tunisia are classified into 4 typical situations: Extremely dry seasons with a few short and weak rainfall events, dry seasons, with high frequency of weak events, intermediate seasons with medium amount of rain and intermittent events and rainiest seasons with long and intense events. The regionalization yields two geographical regions: northern sector characterized by rainy seasons, whereas the stations of the southern sector are mostly dry. The temporal variability analysis shows that the dry season classes dominate extending over three consecutive decades from 1970 to 2000.
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| 8. |
- Fan, X. F., et al.
(författare)
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Increased discharge across the Yellow River Basin in the 21st century was dominated by precipitation in the headwater region
- 2022
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Ingår i: Journal of Hydrology-Regional Studies. - : Elsevier BV. - 2214-5818. ; 44
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Tidskriftsartikel (refereegranskat)abstract
- Study region: The Yellow River Basin in China. Study focus: The discharge in the lowlands of a watershed is susceptible to the variations in its high-altitude headwaters in terms of climate, land cover/use and anthropogenic interference. This study not only focuses on the key role of the high-altitude headwaters of the Yellow River Basin (YRB) on the water supply in its droughty downstream lowlands, but also analyzes the contri-butions of the headwaters' changes to affect the variations of discharge in the entire basin especially in the early 21st century compared to the last half of the 20th century. New hydrological insights for the region: The results indicated that more than 1/3 of the actual flow out of the headwaters of the YRB supported the excessive water demand (mainly for irrigation) downstream. The observed discharge (QObs) increased by 44.07% in the YRB as a whole before and after the mutation year 2002 during 1986-2019, and 76.45% of the discharge increment derived from the headwaters. The increasing precipitation in the headwaters dominated the discharge recovery of the YRB, and resulted in a relative increase of 36.28% in the QObs of the entire YRB; whereas the variations of the headwaters in terms of potential evapotranspiration, land cover and water use for human activities have decreased the QObs of the entire YRB by 4.68%, 2.07% and 5.10%, respectively.
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| 9. |
- Jiang, H. R., et al.
(författare)
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Characterizing precipitation uncertainties in a high-altitudinal permafrost watershed of the Tibetan plateau based on regional water balance and hydrological model simulations
- 2023
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Ingår i: Journal of Hydrology Regional Studies. - 2214-5818. ; 47
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Tidskriftsartikel (refereegranskat)abstract
- Study region: the source region of the Yangtze River (SRYR) Study focus: Precipitation uncertainties significantly impact water resource management, while the uncertainties of various precipitation products are not fully investigated due to the lack of observations, especially in high-altitudinal permafrost areas. In this study, we selected nine products representing three types of precipitation, including gauge-based, satellite-based and merged products, and conducted a comprehensive evaluation using regional water balance method and hydrological model simulations. New hydrological insights for the region: Our results indicate most precipitation products can replicate the observed precipitation decreasing trend with increasing elevation below 4500 m, but trends vary at higher elevations. The gauge-based precipitation products with bias correction outperform others, while most satellite-based products underestimate precipitation. The water -balance based evaluation shows a merged product (TPHiPr), and two gauge-based products perform best, followed by a satellite-based product (MSWEP). Process-based model simulations driven by selected precipitation products can reproduce daily runoff processes well in the entire SRYR (NSE = 0.68-0.86), but the performance degraded in the high-altitudinal Tuotuohe sub -basin (NSE = 0.08-0.76). The runoff coefficients comparisons in these two regions also indicate the possible deficiencies of precipitation products in the high-altitudinal regions. Our results highlight the challenges of current precipitation products in characterizing the spatial and tem-poral precipitation changes in the high-altitudinal permafrost regions, and call for more accurate products in these areas.
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| 10. |
- Klante, Clemens
(författare)
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Brownification in Lake Bolmen, Sweden, and its relationship to natural and human-induced changes
- 2021
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Ingår i: Journal of Hydrology: Regional Studies. - : Elsevier BV. - 2214-5818. ; 36
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Tidskriftsartikel (refereegranskat)abstract
- Study regionThis study focuses on the twelfth largest lake in Sweden, Lake Bolmen and its catchment.Study focusDuring the last decades the process of brownification has resulted in water with browner color, affecting water quality and ecosystems. The occurrence of brownification and its governing factors, especially with regard to the interaction with the environment, is not yet fully understood. This study therefore performed different statistical analysis to detect spatial and temporal patterns in brown color and associated forcing factors. In addition, models were developed to describe the water flows in the lake and their influence on the water color.New hydrological insights for the regionSeasonal variations in color are dominated by meteorological parameters such as precipitation and temperature, whereas long-term (decadal) variations are functions of trends in these parameters as well as changes in land use, primarily related to forestry. Modeling the water flows yielded the residence time for different sub-basins in the lake, indicating the effects of travel time on the color. Calculated wind-generated surface waves and their effects on resuspension showed that such events may occur on a limited event and time scale.
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