Drought trends projection under future climate change scenarios for Iran region

accuracy of the SPEI compared to other indices in different provinces of Iran has been reported by Zarei et al. [27]. The benefit of SPEI has been indicated in several investigations as well. Uddin et al (2020) mentioned that SPEI performs better than SPI because evaporative demand has a positive impact on defining drought conditions [28]. Wang et al. (2021) revealed that SPEI can be used to delineate spatial–temporal evolution of drought, drought characteris- tics, and impacts of drought at the regional and global scales which confirms the advantages of this drought index [29]. Accordingly, the SPEI was used in this study to evaluate drought conditions. The determination of drought threats using the SPEI method was first introduced by [7] as a method that depends on two major parameters–temperature and precipitation. Being that temperature is the major variable in PET calculation, drought conditions are mainly deter- mined by considering the variation between precipitation (P) and PET: Di ¼ Pi PETi ð1Þ Estimating accumulated probabilities of Di by probability density function is essential to calculate SPEI [30]. Due to negative values in Di, the probability density function of a three- Fig 1. Geographical location of the selected stations in Iran. (▲: Tropical steppe: Semi-arid; hot, ◆: Interior Mediterranean: Mild winter; dry summer; hot summer, ●: Mid-latitude desert: Arid; cool or cold, □: Mid-latitude steppe: Semi-arid; cool or cold, ■: Tropical desert: Arid; hot). https://doi.org/10.1371/journal.pone.0290698.g001 PLOS ONE

Drought trends projection under future climate change scenarios for Iran region PLOS ONE | https://doi.org/10.1371/journal.pone.0290698 November 9, 2023 4 / 24