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1、18th World IMACS / MODSIM Congress, Cairns, Australia 13-17 July 2009 http:/mssanz.org.au/modsim09 Ensemble modelling of impact of climate change on runoff regime of Latvian rivers Bethers, U. 1 and J. Sennikovs 1 1 Laboratory for Mathematical Modeling of Environmental and Technological Processes, F
2、aculty of Physics and Mathematics, University of Latvia Email: betherslatnet.lv Abstract: The aim of the present study was to evaluate the impact of climate change on the runoff of the rivers in Latvia. The study was part of the research conducted within the framework of the Latvian National Researc
3、h Programme on the “Impact of the Climate Change on the Latvian Water Environment”. Latvia is a northeastern European country on the eastern coast of the Baltic sea. Its area is 64500 sq. km. The Latvian climate is temperate and mildly varies from rather maritime in the western part of the country t
4、o rather continental in the eastern part. Despite the presence of several hill areas (highest “peak” being 312 m above sea level), the territory can be characterized as lowlands with rather dense river network. Precipitation is common throughout the year with the heaviest rainfalls in July/August. P
5、ermanent snow cover is characteristic for winter months, typically causing spring snow-melt floods. In this study, a two-way ensemble prediction approach was applied for the evaluation of the future river runoff from the territory of Latvia: (1) An ensemble of regional climate models (RCMs) accessib
6、le via the European Commission research project “PRUDENCE” EVK2-CT2001-00132 (prudence.dmi.dk; Christensen, 2007) was considered for the Eastern Baltic area. The regional climate models have built-in runoff models. Comparison of RCM calculations for the reference (or control) time period 1961-1990 a
7、nd for the climate change scenario A2 for time period 2071-2100 allows ensemble evaluation of run-off change forecast for territory of Latvia. (2) The ensemble of hydrological models was used to calculate the climatic time series of runoff from selected catchments in Latvia. The applied models inclu
8、ded the conceptual model MIKE BASIN, and the temporally and spatially distributed physically based models MIKE SHE (both commercial models from DHI group, Denmark; ) and FIBASIN (academic model by University of Latvia; Bethers, 2007). To proceed with the usage of the ensemble of hydrological models
9、for the runoff forecast, we employed several steps: An ensemble of river runoff models was calibrated for the river basins of Latvia using observed climatic (temperature, precipitation) and discharge data series by the Latvian Environmental, Geological and Meteorological Agency (www.legma.gov.lv). T
10、he regional variation (mainly seasonal) of runoff regime was investigated for Latvian rivers for contemporary climate. The RCM calculation results were prepared to serve as input data for the hydrological models via modification of the RCM output by histogram equalization method (Seikovs, 2009) to a
11、ssure statistical compliance of observed and calculated meteorological data series for the control time period. The downscaling procedure was employed for temperature, precipitation and relative humidity data series for contemporary climate (1961-1990) and climate change scenario A2 (2071-2100). The
12、 ensemble of calibrated hydrological models was used for the calculations of the runoff time series for a selected river basin (Brze river in central Latvia). The results of hydrological calculations for contemporary climate allowed evaluation of the usage of modified RCM data as the substitute for
13、the meteorological observation inputs in the hydrological models. The results of hydrological calculations for future climate allowed ensemble evaluation of future runoff regime. Finally, the simplest model (MIKE BASIN) was used to show the expected changes in the regional variation of the runoff re
14、gime. Keywords: Climate change, hydrological modeling, river runoff, model ensemble 3900Bethers Sennikovs, 2009). Therefore, we used the delta change approach, comparing the differences between the contemporary and future model calculations. The considered parameters were (1) the relative change of
15、the mean annual runoff (QA2-QCTL)/QCTL and (2) the relative change of the maximum monthly runoff. The first parameter characterises the overall runoff change, whilst the second shows the trend in the snowmelt flood (or seasonal rainfall) intensity. The forecast of the change of hydrological regime o
16、f pilot river basin according to these two parameters by the RCM ensemble is shown in Figure 2. It represents the existing uncertainty whether the river runoff under the climate change conditions will decrease (probably, yes), and illustrates the possibility that maximum monthly runoff (presently determined by the snowmelt flood) may be of the same order in future climate scenario (determined by maximum rainf
