TY - JOUR A1 - Wambura, Frank Joseph A1 - Dietrich, Ottfried A1 - Lischeid, Gunnar T1 - Improving a distributed hydrological model using evapotranspiration-related boundary conditions as additional constraints in a data-scarce river basin JF - Hydrological processes N2 - Many hydrological models have been calibrated and validated using hydrographs alone. Because streamflow integrates water fluxes in space, many distributed hydrological models tend to have multiple feasible descriptions of hydrological processes. This equifinality usually leads to substantial prediction uncertainty. In this study, additional constraintsnamely, the spatial patterns of long-term average evapotranspiration (ET), shallow groundwater level, and land cover changewere used to investigate the reduction of equifinality and prediction uncertainty in the Soil and Water Assessment Tool (SWAT) in the Wami River basin in Tanzania. The additional constraints were used in the set-up, parameter emulation and calibration of the SWAT model termed an improved hydrological model (IHM). The IHM was then compared with a classical hydrological model (CHM) that was also developed using the SWAT model but without additional constraints. In the calibration, the CHM used only the hydrograph, but the IHM used the hydrograph and the spatial pattern of long-term average ET as an additional constraint. The IHM produced a single, unique behavioural simulation, whereas the CHM produced many behavioural simulations that resulted in prediction uncertainty. The performance of the IHM with respect to the hydrograph was more consistent than that of the CHM, and the former clearly captured the mean behaviour of ET in the river basin. Therefore, we conclude that additional constraints substantially reduce equifinality and prediction uncertainty in a distributed hydrological model. KW - data scarcity KW - equifinality KW - evapotranspiration KW - parameter emulation KW - prediction uncertainty KW - SWAT Y1 - 2018 U6 - https://doi.org/10.1002/hyp.11453 SN - 0885-6087 SN - 1099-1085 VL - 32 IS - 6 SP - 759 EP - 775 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Wambura, Frank Joseph A1 - Dietrich, Ottfried A1 - Lischeid, Gunnar T1 - Evaluation of Spatio-Temporal Patterns of Remotely Sensed Evapotranspiration to Infer Information about Hydrological Behaviour in a Data-Scarce Region JF - Water N2 - Information about the hydrological behaviour of a river basin prior to setting up, calibrating and validating a distributed hydrological model requires extensive datasets that are hardly available for many parts of the world due to insufficient monitoring networks. In this study, the focus was on prevailing spatio-temporal patterns of remotely sensed evapotranspiration (ET) that enabled conclusions to be drawn about the hydrological behaviour and spatial peculiarities of a river basin at rather high spatial resolution. The prevailing spatio-temporal patterns of ET were identified using a principal component analysis of a time series of 644 images of MODIS ET covering the Wami River basin (Tanzania) between the years 2000 and 2013. The time series of the loadings on the principal components were analysed for seasonality and significant long-term trends. The spatial patterns of principal component scores were tested for significant correlation with elevations and slopes, and for differences between different soil texture and land use classes. The results inferred that the temporal and spatial patterns of ET were related to those of preceding rainfalls. At the end of the dry season, high ET was maintained only in areas of shallow groundwater and in cloud forest nature reserves. A region of clear reduction of ET in the long-term was related to massive land use change. The results also confirmed that most soil texture and land use classes differed significantly. Moreover, ET was exceptionally high in natural forests and loam soil, and very low in bushland and sandy-loam soil. Clearly, this approach has shown great potential of publicly available remote sensing data in providing a sound basis for water resources management as well as for distributed hydrological models in data-scarce river basins at lower latitudes. KW - evapotranspiration KW - hydrological behaviour KW - land cover change KW - MODIS ET KW - principal component analysis KW - shallow groundwater Y1 - 2017 U6 - https://doi.org/10.3390/w9050333 SN - 2073-4441 VL - 9 SP - 297 EP - 315 PB - MDPI CY - Basel ER - TY - JOUR A1 - Fahle, Marcus A1 - Dietrich, Ottfried T1 - Estimation of evapotranspiration using diurnal groundwater level fluctuations: Comparison of different approaches with groundwater lysimeter data JF - Water resources research N2 - In wetlands or riparian areas, water withdrawal by plants with access to groundwater or the capillary fringe often causes diurnal groundwater fluctuations. Various approaches use the characteristics of these fluctuations for estimation of daily groundwater evapotranspiration rates. The objective of this paper was to review the available methods, compare them with measured evapotranspiration and assess their recharge assumptions. For this purpose, we employed data of 85 rain-free days of a weighable groundwater lysimeter situated at a grassland site in the Spreewald wetland in north-east Germany. Measurements of hourly recharge and daily evapotranspiration rates were used to assess the different approaches. Our results showed that a maximum of 50% of the day to day variance of the daily evapotranspiration rates could be explained by the approaches based on groundwater fluctuations. Simple and more complex methods performed similarly. For some of the approaches, there were indications that erroneous assumptions compensated each other (e.g., when overestimated recharge counteracted underestimated storage change). We found that the usage of longer time spans resulted in improved estimates of the daily recharge rates and that the estimates were further enhanced by including two night averages. When derived from fitting estimates of recharge or evapotranspiration with according measurements the specific yield, needed to convert changes in water level to water volumes, differed considerably among the methods (from 0.022 to 0.064). Thus, the specific yield can be seen as correction factor that compensates for inadequate process descriptions. KW - evapotranspiration KW - groundwater lysimeter KW - specific yield KW - diurnal signal KW - phreatophytes KW - wetland Y1 - 2014 U6 - https://doi.org/10.1002/2013WR014472 SN - 0043-1397 SN - 1944-7973 VL - 50 IS - 1 SP - 273 EP - 286 PB - American Geophysical Union CY - Washington ER - TY - GEN A1 - Dietrich, Ottfried A1 - Schweigert, Susanne A1 - Steidl, Jörg A1 - Lischeid, Gunnar T1 - Effects of data and model simplification on the results of a wetland water resource management model T2 - Water N2 - This paper presents the development of a wetland water balance model for use in a large river basin with many different wetlands. The basic model was primarily developed for a single wetland with a complex water management system involving large amounts of specialized input data and water management details. The aim was to simplify the model structure and to use only commonly available data as input for the model, with the least possible loss of accuracy. Results from different variants of the model and data adaptation were tested against results from a detailed model. This shows that using commonly available data and unifying and simplifying the input data is tolerable up to a certain level. The simplification of the model has greater effects on the evaluated water balance components than the data adaptation. Because this simplification was necessary for large-scale use, we suggest that, for reasons of comparability, simpler models should always be applied with uniform data bases for large regions, though these should only be moderately simplified. Further, we recommend using these simplified models only for large-scale comparisons and using more specific, detailed models for investigations on smaller scales. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 442 KW - wetland KW - water balance KW - water balance model KW - evapotranspiration KW - groundwater level Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-407579 ER - TY - JOUR A1 - Dietrich, Ottfried A1 - Schweigert, Susanne A1 - Steidl, Jörg A1 - Lischeid, Gunnar T1 - Effects of Data and Model Simplification on the Results of a Wetland Water Resource Management Model JF - Water N2 - This paper presents the development of a wetland water balance model for use in a large river basin with many different wetlands. The basic model was primarily developed for a single wetland with a complex water management system involving large amounts of specialized input data and water management details. The aim was to simplify the model structure and to use only commonly available data as input for the model, with the least possible loss of accuracy. Results from different variants of the model and data adaptation were tested against results from a detailed model. This shows that using commonly available data and unifying and simplifying the input data is tolerable up to a certain level. The simplification of the model has greater effects on the evaluated water balance components than the data adaptation. Because this simplification was necessary for large-scale use, we suggest that, for reasons of comparability, simpler models should always be applied with uniform data bases for large regions, though these should only be moderately simplified. Further, we recommend using these simplified models only for large-scale comparisons and using more specific, detailed models for investigations on smaller scales. KW - wetland KW - water balance KW - water balance model KW - evapotranspiration KW - groundwater level Y1 - 2016 U6 - https://doi.org/10.3390/w8060252 SN - 2073-4441 VL - 8 PB - MDPI CY - Basel ER -