Urban Drainage Systems Risk Assessment under Climate Change Conditions

There is growing interest in assessment of the potential impacts of climate change on urban water systems in light of severe urban flood occurrences. Urban drainage systems are integral components of urban water systems on which climate change may impose adverse impacts such as increase in pluvial flood risk. It is therefore, imperative to take account of increased flood risks due to potential climate variability in preparing/making decisions regarding urban drainage systems implementation. Pluvial flood risk resulting from variations in rainfall patterns due to climate change (IPCM4 model under scenario B1) is evaluated here for varying urban drainage Scenarios namely green roof, pervious pavement, detention pond and channels enlargement designed and simulated for and added to part of an existing urban drainage system of 22nd municipal district of Tehran city (Iran). The output of climate model IPCM4 under B1 scenario, are downscaled by Lars-WG model and IDF curves are then derived by empirical methods for 2046 to 2065. By comparing RMSE errors between current IDF curves and Future IDF curves under B1 scenario, it is estimated that current rainfall events with return periods 2, 5, 10, 20, 50, and 100 years will occur as rainfalls with corresponding return periods 1, 2, 2.6, 4, 7.9 and 13.3 years respectively under climate change condition. Pluvial flood risks are estimated for different return period rainfalls (2, 5, 10, 20, 50, 100 years) under current climate and for corresponding return periods under climate change scenario. Results show flood risks are considerably increased under climate change conditions. Presented methodology can suitably help managers to wisely select urban drainage strategies which have lesser flood risk faced with current and future climate conditions.