Spatially differentiated managementrevised discha

Authors: Tobias Conradt Hagen Koch Fred F Hattermann Frank Wechsung

Publish Date: 2012/01/18

Volume: 12, Issue: 3, Pages: 633-648

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Abstract

A spatially differentiated managementrevised projection of natural water availability up to 2053 was requested for a basinwide scenario study about the impact of global change in the Elbe River basin Detailed discharge and weather information of the recent years 1951–2003 were available for model calibration and validation However the straightforward “classic” approach of calibrating a hydrological model on observed data and running it with a climate scenario could not be taken because most observed river runoffs in Central Europe are modified by human management This paper reports how the problem was addressed and how a major projection bias could be avoided The ecohydrological model SWIM was set up to simulate the discharge dynamics on a daily time step The simulation area of 134890 km² was divided into 2278 subbasins that were subdivided into more than 47500 homogeneous landscape units hydrotopes For each hydrotope plant growth and water fluxes were simulated while river routing calculation was based on the subbasin structure The groundwater module of SWIM had to be extended for accurate modelling of low flow periods After basinscale model calibration and revisions for known effects of lignite mining and water management evapotranspiration and groundwater dynamics were adjusted individually for more than 100 subareas largely covering the entire area A quasinatural hydrograph was finally derived for each subarea taking into account management data for the years 2002 extremely wet and 2003 extremely dry The validated model was used to access the effect of two climate change scenarios consisting of 100 realisations each and resembling temperature increases of 2 and 3 K respectively Additionally four different land use scenarios were considered In all scenario projections discharge decreases strongly The observed average discharge rate in the reference period 1961–1990 is 171 mm/a and the scenario projections for the middle of the twentyfirst century give 91–110 mm/a mainly depending on the climate scenario The areaaveraged evapotranspiration increases only marginally within the scenario period eg from about 570 to about 580 mm/a for the temperature increase of 2 K while potential evapotranspiration increases considerably from about 780 to more than 900 mm/a Both discharge and evapotranspiration changes vary strongly within the basin correlating with elevation The runoff coefficient that globally decreases from 0244 to 0160 in the 2 K scenario is locally governed primarily by land use 68 of the variance of the decreases can be attributed to this factorThe authors would like to express their gratitude to all project partners involved for the good cooperation especially for numerous valuable remarks during the process of calibration and validation Sincere thanks are given to the German Federal Ministry for Education and Research BMBF and the project management agency at the German Aerospace Center PTDLR for the funding of the GLOWAElbe project grant no 01 LW 0603 A2

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