Evaluating the effects of climate change on the amount of groundwater recharge in Karaj Watershed

Climate change is one of the most important challenges that influening natural ecosystems and have different effects on precipitation, temperature, intensity and frequency of droughts and floods and hydrological parameters of watersheds. The purpose of this study is to investigate the effect of climate change on the trend of changes in temperature, precipitation and solar radiation and also to determine the effect of changes in these variables on the recharge of the Karaj watershed. In this study first using the outputs of the two HadCM3 and CGCM1 global models, and using SDSM micro-scale model, climatic variables were simulated for three decades (2010- 2039, 2040-2069 and 2070-2098). In the next step, using HELP model, the rate of groundwater recharge was estimated and the effect of changing these variables on the amount of natural recharge was investigated. Also the results showed that this model is highly sensitive to evapotranspiration. Result of simulating climatic variables under A2 climate change scenario show that in future decades, amount of temperature, precipitation and solar radiation will be increase (1.5, 2.8 and 4.55 percent), decrease (8.1, 15.1 and 18 percent) and increase (0.5, 1.4 and 2.4 percent), respectively. Result of simulating the amount of groundwater recharge using model under A2 climate change scenario show that in future decades, amount of groundwater recharge will be decrease (9.6, 15.1 and 15.6 percent). Also research result show that HELP model is highly sensitive to evapotranspiration amount.