Seasonally dependent precipitation changes and their driving mechanisms in Southwest Asia

Quantifying seasonally varying temperature and precipitation changes is important, particularly in relatively dry regions that are highly vulnerable to climate change. The ERA5 dataset is used here to examine long-term (1979-2020) near-surface temperature and precipitation changes and to understand the driving mechanisms for precipitation changes over Southwest Asia in different seasons. Precipitation and its changes are also analysed based on the CRU dataset. Significant warming trends with strong seasonal and regional differences are identified over Southwest Asia, with the greatest warming trend in spring, followed in decreasing order by winter, summer, and autumn. Mountain temperatures have also increased much faster than other regions in Southwest Asia, particularly in winter and spring. Based on both ERA5 and CRU, precipitation has significantly decreased over parts of southwestern and eastern Iran and southwestern Pakistan in winter but has significantly increased over the Caucasus in spring. Precipitation has not changed significantly over Southwest Asia in summer, while it has significantly increased over parts of Saudi Arabia in autumn. As the CRU dataset only covers land areas, analysis based on ERA5 indicates that precipitation has significantly decreased and increased over the Oman Sea in winter and the Persian Gulf in autumn, respectively. Wind speeds between 400 and 100 hPa levels and mean sea level pressure (MSLP) are also analysed during the period 1979-2020. The subtropical jet has risen significantly over eastern parts of Southwest Asia (55-65(circle)E) in autumn. In winter, the jet has shifted poleward, which resulted in robust decreasing precipitation trends over most parts of Iran and southwestern Pakistan. Over northwestern Iran, however, precipitation has increased in winter in response to a significant decrease in MSLP. In autumn, an equatorward shift of the jet has been accompanied by a significant decrease in MSLP and an increase in precipitation at lower latitudes (20-37(circle)N) of Southwest Asia.

Automated summary

This study examines the temperature and precipitation changes in Southwest Asia using the ERA5 and CRU datasets. The results show significant warming trends in the region, with notable differences between seasons and regions. In terms of precipitation, some areas experience significant decreases in winter while others see significant increases in spring.