Observed and projected changes in temperature and precipitation extremes based on CORDEX data over Iran

Due to increasing greenhouse gases, Iran is experiencing changes in patterns and trends of extreme climate events. Future climate extremes are one of the hottest topics affecting agricultural, economical, and environmental balances in many regions. Here, changes in temperature and precipitation extremes are investigated for the observational (1976-2005) and future (2025-2054) periods over Iran. For this, temperature and precipitation data of the CORDEX project acquired from three regional climate models with RCP4.5 and RCP8.5 scenarios are simulated using a developed multiscale bias correction downscaling method. For identifying trends and changes in 14 extreme climate indices used in this study from 54 climatic stations, the Mann-Kendall test and Sen's slope estimator are used. Results show that notable changes can be seen in the climate extremes across Iran for both observed and projected data. Overall, more warming and increasing trends are found for both maximum and minimum values of daily maximum and minimum temperatures, which rise from RCP4.5 to RCP8.5. The number of cold days and nights indicate decreasing trends; alternatively, the number of warm days and nights show opposite behaviors. Changes in the monthly maximum 1-day and consecutive 5-day precipitation illustrate an increasing trend in most model-scenarios for the projected data in the future compared to the observed one. The spatial analysis results reveal that changes in the climate extremes are more noticeable in the northwestern and western regions of Iran. These areas will probably experience heavy disastrous rainfall because the number of very wet days and heavy precipitation days will increase in the future. Changes in climate extremes will likely increase the risk of severe extreme events in the future in these areas and, consequently, make society more vulnerable to natural disasters. The findings of this study can help decision-makers consider appropriate management in the face of climate change consequences.