Extraction of Intensity-Duration-Frequency (IDF) curves and precipitation change process under the impact of climate change (Case study: Mehrabad synoptic station, Tehran)

In this research, the changes in the frequency intensity curve for the Zone No. 6 of Tehran municipality (Mehrabad synoptic station) under the influence of climate change were investigated by using the Abkhezr-Ghahreman relationship. The information related to the current research includes two categories: First category includes hourly rainfall data measured in order to derive IDF curves for the base period (1980-2020). The second category includes the predicted daily rainfall data for the near future (2021-2050) and the far future (2051-2100), which were obtained from the output of the LARS model. First, using EasyFit software, statistical analysis was done on the observational data and the best distribution (Gamble distribution) was selected and the corresponding IDF curves were extracted for different return periods. To extract the IDF curves under the influence of climate change, the general circulation model of the atmosphere HadGEM - ES from the series of CMIP5 models under RCP2.6, RCP4.5 and RCP8.5 emission scenarios was used. The results showed that the rainfall intensity in all rainfall interval duration and different return periods in all three scenarios have increased compared to the intensity duration frequency curve of the base period, and only for the near future (2021-2050) under the RCP 8.5 scenario, there is a decreasing trend compared to the base period will have. For example, interval duration of 4 and 24 hours for the return period of 10 years, the amount of precipitation intensity for the scenario RCP 2.6 and RCP 8.5 for the distant future (2051 -2100) is 7.05, 7.1 and 2.56, 2.58, respectively, while which for the base period (1980-2020) is 6.71 and 2.44, respectively, which indicates the increase in the intensity of maximum rainfall with the increase of the return period. It can be concluded that the maximum intensity of rainfall has increased in short-term time base and with the passage of time, the intensity of the maximum rainfall has decreased, and the IDF curves are affected by short-term rainfall.