Prediction of future drought in the Keygooran Juniper forest reserve of Iran using standardized precipitation evapotranspiration index (SPEI)

Drought is a major threat to vegetation and can cause its decline. Due to natural and human factors, droughts are becoming more frequent and intense around the world. This research examines the trend and severity of droughts in the past and future using the standardized precipitation evapotranspiration index (SPEI) for a Juniper forest reserve in Keygooran, Lorestan Province, Iran. The SPEI index was calculated using daily precipitation and temperature data from the Aligudarz synoptic station for a 33-year period (1987-2019). The frequency and severity of droughts were assessed for the recent past (1987-2019) and the future (2030-2060) using the NorESM2-LM model under the SSP126, SSP370 and SSP585 scenarios. The results showed that the longest droughts occurred in 1990-1991, 1998-2000 and 2010-2012. Moreover, 2003, 2013, 2017 and 2018 were the years with the most severe droughts. In the future (2030-2060), drought periods will be projected to decrease under the SSP126 and SSP585 scenarios (6, 9 and 12 months) and increase under the SSP370 scenario (3, 9 and 12 months). The intensity and duration of extremely severe droughts will be projected to increase in the future despite the decrease in drought frequency based on SPEI. Therefore, the Juniper forest reserve will face more severe droughts in the future, which will affect the reproduction of juniper trees significantly.