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Projected changes in extreme precipitation events over Iran in the 21st century based on CMIP5 models

Mohammad Darand*

*Corresponding author:

ABSTRACT: Climate extremes have large impacts on human societies and natural ecosystems. Projection of changes in climate extremes is very important for long term planning. The current study investigated future changes in extreme precipitation events over Iran based on eighteen CMIP5 models for the period 2006–2100. National gridded extreme precipitation data in the Asfazari database was used to evaluate climate model simulation of extreme precipitations. Results indicated that models with higher spatial resolution (CCSM4 and MRI-CGCM3) perform better than those with lower resolutions in capturing the spatial features of extreme precipitation events. Bias correction was applied to models before projecting changes in extreme precipitation events. The projected changes were assessed with the nonparametric modified Mann-Kendal trend test and Sen slope estimator at 95% confidence level. The findings illustrated that annual total precipitation (PRPCTOT) and rainy days (RD) were projected to decrease but the intensity and frequency of precipitation extremes were predicted to increase significantly. The projected decrease was larger in northwestern parts than other regions, with decrease values of 18 to 22 mm decade–1 and 4 to 4.8 d decade–1, respectively. Although there were discrepancies in the changing rates between the models, the extreme precipitation events over the Iran was generally projected to increase in the twenty-first century. An increase in consecutive dry days (CDD) was predicted for most parts of Iran by the end of the twenty-first century under RCP8.5 scenario with the largest increase of up to 5 to 6.8 d decade–1 found for northwestern Iran. In half of the eastern part of Iran where precipitation occurs extremely rarely, the number of days with daily precipitation exceeding 10 mm (R10) or even 20 mm (R20) were projected to increase significantly. Conclusively, these changes suggest an increased risk of flash floods in Iran from increased extreme precipitation under the RCP8.5 emission scenario.