Assessment the Intensity of the Effect of Climate Change on Groundwater Resources of Varamin plain using NISTOR index

The aim of this study was to investigate the Intensity of the effect of climate change using CMIP5 group models under RCP scenarios on groundwater resources in Varamin plain. The output of these models was downscaled by LARS-WG .For this purpose, the period(1989-2005)was used as a base period to select the regional model and the period 2050-2021 to study the NISTOR index in the future. The results showed that the EC-EARTH model has a high performance in simulating temperature and precipitation in the study area of CMIP5 series under three scenarios RCP2.6, RCP4.5 and RCP8.5 for the next period. On average, the average temperature in the study area, under the scenarios RCP2.6 and RCP4.5, respectively, predicted an increase of 1 to 1.2 ° C compared to the base period, while the same temperature increase based on the most pessimistic scenario That is, RCP8.5 in the period 2050-2020, an average increase of about 1.5 degrees was predicted compared to the base period. Also in future periods, an increase in precipitation was observed in the early months of the year to late spring and a decrease in precipitation in autumn. Overall, the RCP4.5 scenario showed slightly more annual precipitation increase over the next 30 years than the base period over the other two scenarios. Also, the results of the NISTOR index, considering the effective rainfall, and De-martone index showed in all three scenarios, the intensity of effects of climate change on the groundwater resources of Varamin plain in the future is significant