Evaluation of the climate change impact on the intensity and return period for drought indices of SPI and SPEI (study area: Varamin plain)

In this study, to investigate the climate change effect on meteorological drought in the next three decades of Varamin plain, the EC-EARTH model was selected from the (AR5) report with the high performance of temperature and precipitation simulation compared to the base period under RCP scenarios and then by LARS-WG software was downscaled. In addition, (intensity-duration) and the return period of drought indices of Standard precipitation index (SPI) and Standardized precipitation-evapotranspiration index (SPEI) in annual time series were evaluated. Results illustrated that the seasonal precipitation pattern has changed, and mean temperatures will increase by 1.4 °C compared to the base period. The results of the drought assessment showed that the intensity of drought in the future compared to the base period based on SPI and SPEI increased by 8 and 28%, respectively, indicating that the SPEI was more severe in all three scenarios than the SPI. It can mainly be explained by the contribution and effect of increasing the average temperature along with precipitation in the SPEI. Also, the return period of severe droughts under the RCP8.5 scenario for SPEI in the base and future periods is 8 and 6 years, respectively, which indicates a decrease in the return period of severe droughts and an increase in dry years in the future.