Temporal evolution and spatial variation of meteorological drought characteristics in Iran's diverse climates over the past half century

This study investigates the spatiotemporal characteristics of meteorological drought over the past 50 years in Iran's four distinct climates: Hyper-arid, Arid, Semiarid, and Humid. Employing three drought indices (Standardized Precipitation Index, Reconnaissance Drought Index, and Standardized Precipitation Evapotranspiration Index) at multiple timescales (1-, 3-, 6-, 9-, and 12-months), the analysis utilizes data from 41 synoptic meteorological stations spanning the period from 1969 to 2019. Results reveal a temporal increase in the duration and intensity of drought events, particularly post the 1998-99 period. The longest extreme drought, lasting 40 months, occurred during Dec 1998-Mar 2002 and Jan 2018-Mar 2018. Spatial patterns indicate a uniform rise in drought intensity across timescales and indices, transitioning from humid and semiarid to arid and Hyper-arid regions. Average drought durations for SPI, SPEI, and RDI indices are 9, 12, and 9 months, respectively, while mean drought frequencies stand at 14%, 17%, and 13% for SPI, SPEI, and RDI indices. Notably, SPEI exhibits greater duration and frequency of drought events, especially in arid and Hyper-arid regions. The research underscores the pivotal role of climatic variables in delineating drought characteristics and emphasizes the significance of selecting appropriate drought indices across diverse climates.