Increasing risk of meteorological drought in the Lake Urmia basin under climate change: Introducing the precipitation–temperature deciles index

•Meteorological drought is characterized based on precipitation–temperature jointly.•The methodology is applied to the basin of Lake Urmia which has shrunk drastically.•The climate of the region is projected to shift toward drier/hotter conditions.•The irrigation water use of wheat is projected to increase under all scenarios.•The frequency of dry/hot months is projected to increase by 4.7–24.0% in 2060–2080. Meteorological droughts due to the concurrent occurrence of low-precipitation and high-temperature events can lead to severe negative impacts on agriculture, economy, ecosystem, and society. This study proposes a novel framework to characterize such drought conditions based on the joint variability of precipitation–temperature, particularly under climate change. Generalized hierarchical linear model is used to downscale precipitation and temperature at multiple stations from the outputs of nine General Circulation Models (GCMs) under Representative Concentration Pathways (RCPs) 4.5 and 8.5. A bivariate drought index called Precipitation–Temperature Deciles Index (PTDI) is developed using copulas to assess changes in future dry/hot conditions. The methodology is applied to the Lake Urmia basin located in a semi-arid region in the northwest of Iran. Lake Urmia, the sixth largest salt lake in the world at the original size, has shrunk dramatically causing environmental and socioeconomic disruptions. Results suggest that the climate of the region is projected to shift toward drier/hotter conditions in the future. The multi-model ensemble means of all GCMs shows an increase of ~4 °C in the regional temperature and ~25 mm (8%) decrease in precipitation in 2060–2080 based on RCP8.5. The magnitude of climate-induced water deficit is projected to increase under all future scenarios. According to the PTDI, projected changes in the number of “extremely dry/hot” months in 2060–2080 under RCP4.5 and RCP8.5 relative to the historical period vary between 2.4 and 7.3% and 4.5–13.2%, respectively. This condition is unfavorable for the revival of the endangered lake while maintaining the agricultural activities in the region.