Evaluating Intensity, Duration and Frequency of Short Duration Rainfalls Using a Regional Climate Change model (Case study: Tehran)

Climate change and global warming are the biggest challenges in the present era which have affected the global and regional hydrologic cycles. Precipitation is one of the climate elements that has been directly affected by rising global average temperatures. One of the most important negative effects of climate change is increasing the intense precipitation and henceforth occurring flash floods. The present study firstly analyzed the trend and jump of the short duration observed rainfalls (10 minutes to 3-hour duration) in the Mehrabad station located in the west of Tehran by using Mann-Kendal and CUSUM approaches, respectively. The trend test indicated an increasing trend in the short duration rainfalls amount at the 99% confidence level while 1978 was distinguished as the jumping year. For using dynamic downscaling to meet the fine spatial resolution required in the present study, the PRECIS regional model was employed to evaluate the changes in the intensity, duration, and frequency of the short duration rainfalls, derived from the daily rainfalls by applying a special time downscaling factor, after the year of the jump for historical data and also under the A2 and B2 emission scenarios for future. The results of the IDF analysis showed that in the far future (2070-2100) the amount and intensity of precipitation would increase significantly over a given return period. There is also a significant increase in the frequency and probability of occurrence of extreme precipitation.