A Study of Rainfall and Urban Runoff Flow Regime under Future Climate Condition (Case study: West Flood-Diversion Catchment in Tehran)

Among the climate change impacts, changing hydrologic regime and increasing the probability of encountering extreme events are of the most important. This paper investigates extreme rainfall and runoff regime (intensity and frequency) under climate change impact in West Flood-Diversion (WFD) catchment in Tehran, and compares the changes in extreme rainfall and runoff return periods during future time period (2080-2090) with baseline period (1999-2000). To do this, the output of MRI-CGCM2.3.2a climate model under A1B emission scenario was extracted as a point (station scale) and change factor method was used for downscaling and producing daily rainfall time series. Afterwards by extracting extreme daily rainfall data, the value of 1-hour, 10-year rainfall of the catchment was calculated and then IDF curves of the catchment for base time period and also the future period were obtained. Finally by extracting PDFs of Maximum runoff, changes in catchment’s runoff regime in future period compared to baseline period were analyzed. The results showed that extreme rainfall intensity at future decreases a little compared to base time period. In addition the results are representative of enhancing catchment’s runoff discharges in 2090 time horizon compared to baseline period. By moving from baseline to the future, the catchment faces increasing in frequency and probability of a given amount of runoff discharge occurrence, and also for a given return period, urban flood flow-rate increases. Therefore employing measures for adaptation to climate change impacts in the catchment seems to be necessary.