The impact of climate change on severity, duration and magnitude of drought using SPI and RDI in Semnan region

Drought monitoring is an essential component of drought risk management. This paper presents characteristics of droughts simulated by 13 global climate models (GCMs) under two greenhouse gases emission (RCP4.5 and RCP8.5) at three levels of risk (0.25, 0.50, and 0.75) in the Semnan region. For this purpose, the Reconnaissance Drought Index (RDI) and standardized precipitation index (SPI) were calculated for three future periods 2010-2039, 2040-2069, and 2070-2099 at different time scales. The calculated RDI and SPI for different climate change scenarios were compared with those of the past period (1965-2009). The results revealed that as compared to the RCP4.5 scenario, in the RCP8.5 scenario, there will be more dry and wet periods. Drought duration predicted by RDI index compared to SPI index (at 1-year and 3-mon time scales), under both emission scenarios in the future period (2010-2099) has decreased compared to the past period (1965-2009), but the number of droughts has increased. Additionally, increases and decreases in the drought magnitude and severity were found at time scales 3-month and annually, respectively. These results provide observational evidence for the increasing risk of droughts as anthropogenic global warming progresses.