Simulating the climate change effects on the Karaj Dam basin: hydrological behavior and runoff

ABSTRACT This study has used Coupled Model Intercomparison Project Phase 5 (CMIP5) and Coupled Model Intercomparison Project Phase 6 (CMIP6). Hence, the runoff simulation was done in near-future period (2030–2050) scenarios by applying climate change conditions for HadGEM2-ES model under three representative concentration pathways RCP2.6, 4.5 and 8.5 scenarios and for HadGEM3-GC31-LL model under SSP1-2.6, SSP2-4.5 and SSP5-8.5 scenarios. Examining the climatic precipitation variables and minimum and maximum temperature under climate change conditions showed a temperature increase of 1.51–2.91 °C for all models and scenarios and a precipitation decrease of 0.05–11.15% for most of them, and the SWAT model simulation showed a runoff decrease in all four stations under SSP scenarios and a runoff increase in three stations under RCP scenarios. Since the climate data for SSP scenarios have become available only recently, results of this study predict that the overall future flow will vary in the −5 to 28% range, resulting in a 5–35% decrease in the flow and, hence, a decrease in the inflow to the dam reservoir. Based on the results, there is a possibility of a 5–30% reduction of the runoff entering the dam reservoir.