Investigating the effects of climate change on torrential rains in Tehran province

The phenomenon of climate change and global warming is one of the biggest challenges of the present age, which has affected the hydrological cycle on a global and regional scale. The purpose of this study is to investigate the effects of climate change on torrential rains And Temprature, Rainfall, Run off  in Tehran province. In this study, changes in torrential rainfall in Tehran and the frequency and intensity of torrential rainfall in the future and climate change and the rate of increase of floods on periodic floods have been investigated.

This research has been done in two study discussions (meteorological, hydrological). First, parameters (temperature and precipitation) for synoptic stations (Abali, Shemiran, Mehrabad) for the period (1988-2020) were received from the Meteorological Organization and rainfall and runoff data from hydrometric stations were received from the Tehran Regional Water Authority. Down Scaling model and methods in this research SDSM-DC, Mann-Kendall, Rclimdex, XLSTAT, to simulate future floods and SMADA, HEC-HMS model to simulate floods in current and future periods have been used.

The results showed that the temperature extreme indices in all stations had an increasing trend and the precipitation indices had an increasing trend only in Abali station. But rainfall in Shemiran and Mehrabad stations had a decreasing trend. Examination of rainfall changes using Mann-Kendall test in most months of the year shows a stable trend and jumps are observed in the rainy months, which can be justified by the increase in rainfall frequency. In the CanESM Model 2 simulation, emphasizing the RCP8.5 release scenario, an increasing temperature trend was observed for the coming decades. The highest temperature increase belongs to Mehrabad station with an average temperature increase of 5.1 percent for the period 2021-2083. The highest rainfall for all three stations is estimated in March next year. Therefore, with the increase of temperature trend, changes in the type of precipitation have occurred, which can be affected by urban microclimate. Simulation of the rainfall-runoff model of the basin with the HEC-HMS model showed that the volume of discharge in the future will be reduced by 5 percent and for return periods, the maximum discharge is estimated at 1501.7 cubic meters.

Due to Rainfall behavior is expected to increase in the coming decades, while reducing its fluctuations. It is predicted that the climate of Tehran in the future will have more fluctuations in precipitation and warmer than the current situation, and this increase and frequency of precipitation is likely to increase flood frequency and reinforce its occurrence, while rainfall will occur more accidentally but with greater intensity, leading to environmental and urban hazards.