| 1. |
- Westerberg, Ida, et al.
(författare)
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Precipitation data in a mountainous catchment in Honduras: quality assessment and spatiotemporal characteristics
- 2010
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Ingår i: Theoretical and Applied Climatology. - : Springer Nature. - 0177-798X .- 1434-4483. ; 101:3-4, s. 381-396
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Tidskriftsartikel (refereegranskat)abstract
- An accurate description of temporal and spatial precipitation variability in Central America is important for local farming, water supply and flood management. Data quality problems and lack of consistent precipitation data impede hydrometeorological analysis in the 7,500 km2 Choluteca River basin in central Honduras, encompassing the capital Tegucigalpa. We used precipitation data from 60 daily and 13 monthly stations in 1913–2006 from five local authorities and NOAA's Global Historical Climatology Network. Quality control routines were developed to tackle the specific data quality problems. The quality-controlled data were characterised spatially and temporally, and compared with regional and larger-scale studies. Two gapfilling methods for daily data and three interpolation methods for monthly and mean annual precipitation were compared. The coefficient-of-correlation-weighting method provided the best results for gap-filling and the universal kriging method for spatial interpolation. In-homogeneity in the time series was the main quality problem, and 22% of the daily precipitation data were too poor to be used. Spatial autocorrelation for monthly precipitation was low during the dry season, and correlation increased markedly when data were temporally aggregated from a daily time scale to 4–5 days. The analysis manifested the high spatial and temporal variability caused by the diverse precipitationgenerating mechanisms and the need for an improved monitoring network.
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| 2. |
- Reynolds, Eduardo, et al.
(författare)
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Robustness of flood-model calibration using single and multiple events
- 2019
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Ingår i: Hydrological Sciences Journal. - Oxon : Taylor & Francis. - 0262-6667 .- 2150-3435. ; 65:5, s. 842-853
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Tidskriftsartikel (refereegranskat)abstract
- Lack of discharge data for model calibration is challenging for flood prediction in ungauged basins. Since establishment and maintenance of a permanent discharge station is resource demanding, a possible remedy could be to measure discharge only for a few events. We tested the hypothesis that a few flood-event hydrographs in a tropical basin would be sufficient to calibrate a bucket-type rainfall-runoff model, namely the HBV model, and proposed a new event-based calibration method to adequately predict floods. Parameter sets were chosen based on calibration of different scenarios of data availability, and their ability to predict floods was assessed. Compared to not having any discharge data, flood predictions improved already when one event was used for calibration. The results further suggest that two to four events for calibration may considerably improve flood predictions with regard to accuracy and uncertainty reduction, whereas adding more events beyond this resulted in small performance gains.
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| 3. |
- Widén Nilsson, Elin, et al.
(författare)
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Model performance and parameter behavior for varying time aggregations and evaluation criteria in the WASMOD-M global water balance model
- 2009
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Ingår i: Water resources research. - 0043-1397 .- 1944-7973. ; 45:5, s. W05418-
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Tidskriftsartikel (refereegranskat)abstract
- Global discharge estimates commonly range between 36.500 km(3) a(-1) and 44.500 km(3) a(-1), i.e., around 20%, and continental estimates differ much more. Data uncertainties are assumed to be a main cause of simulated runoff uncertainties, but model performance must also be addressed. The parsimonious WASMOD-M global water balance model, using limited input data, was used to assess data and model uncertainty (contrary to models using much data but being modestly or not at all calibrated). A Monte Carlo technique based on 15,000 parameter value sets was used to evaluate the model against four criteria: observed snow and monthly, annual, and long-term discharge. WASMOD-M was overparameterized when evaluated only against long-term average discharge but not against monthly discharge, and its snow algorithm could be simplified. Sequential calibration is suggested for confining the behavioral parameter space and minimizing model equifinality starting with snow, followed by long-term volume error, and ending with discharge dynamics.
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| 4. |
- Gao, Ge, 1972, et al.
(författare)
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Trend of estimated actual evapotranspiration over China during 1960-2002
- 2007
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 112:D11120
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Tidskriftsartikel (refereegranskat)abstract
- In this study, the water balance methodology introduced by Thornthwaite and Mather (1955) is modified to estimate monthly actual evapotranspiration for 686 stations over China during 1960–2002. The modification is done by replacing the Thornthwaite potential evapotranspiration estimation with the Penman-Monteith method. Temporal trend and spatial distribution of the estimated annual actual evapotranspiration during the past 43 years are analyzed. The results show that (1) the actual evapotranspiration had a decreasing trend in most areas east of 100°E, and there was an increasing trend in the west and the north parts of northeast China; (2) the spatial distribution of the trend for the actual evapotranspiration is similar to that of the potential evapotranspiration in south China, while the trends are opposite in north China; (3) for most parts of China, the change in precipitation played a key role for the change of estimated actual evapotranspiration, while in southeast China, the change of potential evapotranspiration appeared to be the major factor; and (4) in general, the hydrological cycle was intensified in western China, whereas it was weakened from the Yellow River basin northward.
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| 5. |
- Wetterhall, Fredrik, et al.
(författare)
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Statistical downscaling of daily precipitation over Sweden using GCM output
- 2009
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Ingår i: Journal of Theoretical and Applied Climatology. - : Springer Science and Business Media LLC. - 0177-798X .- 1434-4483. ; 96:1-2, s. 95-103
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Tidskriftsartikel (refereegranskat)abstract
- A classification of Swedish weather patterns (SWP) was developed by applying a multi-objective fuzzy-rule-based classification method (MOFRBC) to large-scale-circulation predictors in the context of statistical downscaling of daily precipitation at the station level. The predictor data was mean sea level pressure (MSLP) and geopotential heights at 850 (H850) and 700 hPa (H700) from the NCEP/NCAR reanalysis and from the HadAM3 GCM. The MOFRBC was used to evaluate effects of two future climate scenarios (A2 and B2) on precipitation patterns on two regions in south-central and northern Sweden. The precipitation series were generated with a stochastic, autoregressive model conditioned on SWP. H850 was found to be the optimum predictor for SWP, and SWP could be used instead of local classifications with little information lost. The results in the climate projection indicated an increase in maximum 5-day precipitation and precipitation amount on a wet day for the scenarios A2 and B2 for the period 2070-2100 compared to 1961-1990. The relative increase was largest in the northern region and could be attributed to an increase in the specific humidity rather than to changes in the circulation patterns.
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| 6. |
- Reynolds, J. Eduardo, et al.
(författare)
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Flood prediction using parameters calibrated on limited discharge data and uncertain rainfall scenarios
- 2020
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Ingår i: Hydrological Sciences Journal. - : Taylor & Francis. - 0262-6667 .- 2150-3435. ; 65:9, s. 1512-1524
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Tidskriftsartikel (refereegranskat)abstract
- Discharge observations and reliable rainfall forecasts are essential for flood prediction but their availability and accuracy are often limited. However, even scarce data may still allow adequate flood forecasts to be made. Here, we explored how far using limited discharge calibration data and uncertain forcing data would affect the performance of a bucket-type hydrological model for simulating floods in a tropical basin. Three events above thresholds with a high and a low frequency of occurrence were used in calibration and 81 rainfall scenarios with different degrees of uncertainty were used as input to assess their effects on flood predictions. Relatively similar model performance was found when using calibrated parameters based on a few events above different thresholds. Flood predictions were sensitive to rainfall errors, but those related to volume had a larger impact. The results of this study indicate that a limited number of events can be useful for predicting floods given uncertain rainfall forecasts.
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| 7. |
- Reynolds, Eduardo, et al.
(författare)
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Sub-daily runoff predictions using parameters calibrated on the basis of data with a daily temporal resolution
- 2017
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Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 550, s. 399-411
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Tidskriftsartikel (refereegranskat)abstract
- Concentration times in small and medium-sized basins (similar to 10-1000 km(2)) are commonly less than 24 h. Flood-forecasting models are thus required to provide simulations at high temporal resolutions (1 h-6 h), although time-series of input and runoff data with sufficient lengths are often only available at the daily temporal resolution, especially in developing countries. This has led to study the relationships of estimated parameter values at the temporal resolutions where they are needed from the temporal resolutions where they are available. This study presents a methodology to treat empirically model parameter dependencies on the temporal resolution of data in two small basins using a bucket-type hydrological model, HBV-light, and the generalised likelihood uncertainty estimation approach for selecting its parameters. To avoid artefacts due to the numerical resolution or numerical method of the differential equations within the model, the model was consistently run using modelling time steps of one-hour regardless of the temporal resolution of the rainfall-runoff data. The distribution of the parameters calibrated at several temporal resolutions in the two basins did not show model parameter dependencies on the temporal resolution of data and the direct transferability of calibrated parameter sets (e.g., daily) for runoff simulations at other temporal resolutions for which they were not calibrated (e.g., 3 h or 6 h) resulted in a moderate (if any) decrease in model performance, in terms of Nash-Sutcliffe and volume-error efficiencies. The results of this study indicate that if sub-daily forcing data can be secured, flood forecasting in basins with sub-daily concentration times may be possible with model-parameter values calibrated from long time series of daily data. Further studies using more models and basins are required to test the generality of these results.
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| 8. |
- Gong, Lebing, et al.
(författare)
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Large-scale runoff generation - parsimonious parameterisation using high-resolution topography
- 2011
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Ingår i: Hydrology and Earth System Sciences. - : Copernicus GmbH. - 1027-5606 .- 1607-7938. ; 15:8, s. 2481-2494
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Tidskriftsartikel (refereegranskat)abstract
- World water resources have primarily been analysed by global-scale hydrological models in the last decades. Runoff generation in many of these models are based on process formulations developed at catchments scales. The division between slow runoff (baseflow) and fast runoff is primarily governed by slope and spatial distribution of effective water storage capacity, both acting at very small scales. Many hydrological models, e. g. VIC, account for the spatial storage variability in terms of statistical distributions; such models are generally proven to perform well. The statistical approaches, however, use the same runoff-generation parameters everywhere in a basin. The TOPMODEL concept, on the other hand, links the effective maximum storage capacity with real-world topography. Recent availability of global high-quality, high-resolution topographic data makes TOPMODEL attractive as a basis for a physically-based runoff-generation algorithm at large scales, even if its assumptions are not valid in flat terrain or for deep groundwater systems. We present a new runoff-generation algorithm for large-scale hydrology based on TOPMODEL concepts intended to overcome these problems. The TRG (topography-derived runoff generation) algorithm relaxes the TOPMODEL equilibrium assumption so baseflow generation is not tied to topography. TRG only uses the topographic index to distribute average storage to each topographic index class. The maximum storage capacity is proportional to the range of topographic index and is scaled by one parameter. The distribution of storage capacity within large-scale grid cells is obtained numerically through topographic analysis. The new topography-derived distribution function is then inserted into a runoff-generation framework similar VIC's. Different basin parts are parameterised by different storage capacities, and different shapes of the storage-distribution curves depend on their topographic characteristics. The TRG algorithm is driven by the HydroSHEDS dataset with a resolution of 3 '' (around 90 m at the equator). The TRG algorithm was validated against the VIC algorithm in a common model framework in 3 river basins in different climates. The TRG algorithm performed equally well or marginally better than the VIC algorithm with one less parameter to be calibrated. The TRG algorithm also lacked equifinality problems and offered a realistic spatial pattern for runoff generation and evaporation.
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| 9. |
- Ngongondo, Cosmo, et al.
(författare)
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Flood frequency under changing climate in the upper Kafue River basin, southern Africa : a large scale hydrological model application
- 2013
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Ingår i: Stochastic environmental research and risk assessment (Print). - : Springer Science and Business Media LLC. - 1436-3240 .- 1436-3259. ; 27:8, s. 1883-1898
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Tidskriftsartikel (refereegranskat)abstract
- The projected impacts of climate change and variability on floods in the southern Africa has not been well studied despite the threat they pose to human life and property. In this study, the potential impacts of climate change on floods in the upper Kafue River basin, a major tributary of the Zambezi River in southern Africa, were investigated. Catchment hydrography was delineated using the Hydro1k at a spatial resolution of 1 km. The daily global hydrological model WASMOD-D model was calibrated and validated during 1971-1986 and 1987-2001 with the simple-split sample test and during 1971-1980 and 1981-1990 with the differential split sample test, against observed discharge at Machiya gauging station. Predicted discharge for 2021-2050 and 2071-2100 were obtained by forcing the calibrated WASMOD-D with outputs from three GCMs (ECHAM, CMCC3 and IPSL) under the IPCC's SRES A2 and B1 scenarios. The three GCMs derived daily discharges were combined by assigning a weight to each of them according to their skills to reproduce the daily discharge. The two calibration and validation tests suggested that model performance based on evaluation criteria including the Nash-Sutcliffe coefficient, Pearson's correlation coefficient (r), Percent Bias and R (2) was satisfactory. Flood frequency analysis for the reference period (1960-1990) and two future time slices and climate change scenarios was performed using the peak over threshold analysis. The magnitude of flood peaks was shown to follow generalised Pareto distribution. The simulated floods in the scenario periods showed considerable departures from the reference period. In general, flood events increased during both scenario periods with 2021-2050 showing larger change. The approach in our study has a strong potential for similar assessments in other data scarce regions.
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| 10. |
- Kauffeldt, Anna, et al.
(författare)
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Imbalanced land surface water budgets in a numerical weather prediction system
- 2015
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 42:11, s. 4411-4417
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Tidskriftsartikel (refereegranskat)abstract
- There has been a significant increase in the skill and resolution of numerical weather prediction models (NWPs) in recent decades, extending the time scales of useful weather predictions. The land surface models (LSMs) of NWPs are often employed in hydrological applications, which raises the question of how hydrologically representative LSMs really are. In this paper, precipitation (P), evaporation (E), and runoff (R) from the European Centre for Medium-Range Weather Forecasts global models were evaluated against observational products. The forecasts differ substantially from observed data for key hydrological variables. In addition, imbalanced surface water budgets, mostly caused by data assimilation, were found on both global (P-E) and basin scales (P-E-R), with the latter being more important. Modeled surface fluxes should be used with care in hydrological applications, and further improvement in LSMs in terms of process descriptions, resolution, and estimation of uncertainties is needed to accurately describe the land surface water budgets.
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