CMIP6-based Assessment of Human contribution to Iran drought in 2021

Abstract

The Iranian Red Crescent Society reported that 4.9 million people over Iran, particularly rural areas, are at medium and high risk of drought impacts. The GPCPv2.3 data show that the 2012 precipitation over Iran was lowest since 1979 while the level of public awareness of the ongoing drought was low, possibly due to the antecedent wet condition in 2020. The Arabian Subtropical High (ASH) expanded and was strong over 2020/21. How unusual the Iran drought in 2021 was? Was it attributable anthropogenic forcings? In this study, an extreme event is the unprecedented Iran drought in the calendar year 2021, defined by the 12-month standardized precipitation index (SPI12) calculated from the regional averages over Iran, excluding desert areas (herein, the long-term annual average less than 0.5 mm/day. First, we evaluate the performance of the 13 CMIP6 models: BCC, CAS, CCCma, CNRM-CERFACS, CSIRO, CSIRO-ARCCSS, IPSL, MIROC, MOHC, MRI, NASA-GISS, NCAR, and NCC for the precipitation seasonality. Second, we use the CMIP6 models that capture well the precipitation seasonality and then construct the SPI12 distributions of the CMIP6 models for individual experiment forcing ensemble runs (historical, greenhouse gas-only, aerosol-only, and natural-only) and their SPI12 distributions over 2002–2021. Lastly, we compute the attributable probability ratio of the 2021-like drought to anthropogenic forcings in terms of drought intensity, persistence, and severity. Lastly, we discuss the need for climate change adaptation for long-lasting Iran drought.