Assessment of Climate Change Impact on the Inflow to Agricultural Reservoir and the Streamflow of a Watershed in South Korea

Abstract

This study is to assess the effect of potential future climate change on the inflow of agricultural reservoir and its impact to downstream streamflow by reservoir operation for paddy irrigation water supply using the SLURP (semi-distributed land use-based runoff process), a physically based hydrological model. Before the future analysis, the SLURP model was calibrated using the 6 years daily streamflow records (1998-2003) and validated using 3 years streamflow data (2004-2006) for a 366.5 km2 watershed including two agricultural reservoirs (Geumgwang and Gosam) located in the upper middle part of South Korea. The calibration and validation results showed that the model was able to simulate the daily streamflow well considering the reservoir operation for paddy irrigation and flood discharge, with a coefficient of determination and Nash-Sutcliffe efficiency ranging from 0.7 to 0.9 and 0.5 to 0.8 respectively. At first, the analysis of historical hydrologic trend was investigated by the simulated SLURP model run using the 30 years weather data from 1977 to 2006 and the results was analysed by Mann-Kendall trend test. Next as a main analysis, the future potential climate change impact was assessed using the CCCma CGCM2 data by SRES (special report on emissions scenarios) A2 and B2 scenarios of the IPCC (intergovernmental panel on climate change). The future weather data for the year 2020s, 2050s and 2080s was downscaled by Change Factor method through bias-correction using 30 years (1977-2006) weather data of 3 meteorological stations of the watershed. In addition, the future land covers were predicted by modified CA (cellular automata)-Markov technique using the time series land cover data from Landsat images. Also the future vegetation cover information was predicted and considered by the linear regression between monthly NDVI (normalized difference vegetation index) from NOAA AVHRR images and monthly mean temperature using eight years (1998 - 2005) data. The future (2020s, 2050s and 2080s) reservoir inflow, the temporal changes of reservoir water level and its impact to downstream streamflow watershed were analyzed for the A2 and B2 climate change scenarios based on a base year (2005) using the prepared future climate data, land cover and vegetation cover information. At an annual temporal scale, the reservoir inflow and water level change of the agricultural reservoir were projected to big decrease in autumn under all possible combinations of conditions. The future streamflow decreased slightly, where as the evapotranspiration was projected to increase largely for all possible combinations of the conditions.