The northern Central Asia is one of the largest dryland regions in the Northern Hemisphere and is facing a crisis of water resources shortage in recent decades.

While the construction of dams, diversion of waterways and wasting of water have been blamed for the shortage, how climate change has influenced regional water resources remains unknown.

In a recently published study in Geophysical Research Letters, JIANG Jie and ZHOU Tianjun from the Institute of Atmospheric Physics (IAP) of the Chinese Academy of Sciences found that the crisis of water resources shortage in northern Central Asia is also resulted from the drying trend since the 1950s.

The researchers highlighted the impacts of human activities on the fragile Central Asian ecosystem by influencing the key atmospheric circulation and local hydrological cycle.

The decreasing rainfall trend is associated with the southward shift and weakening of the subtropical westerly jet. "The subtropical westerly jet is one of the important circulation systems in Eurasia and is closely linked to summer precipitation over northern Central Asia at different time scales," JIANG explained.

The changes in the location and strength of subtropical westerly jet under different forcings, which are associated with the drying trend over northern Central Asia. GHG: greenhouse gas-only historical simulation (red); AA: anthropogenic aerosol-only historical simulation (blue). (Image by JIANG Jie)

To identify and isolate the contributions of greenhouse gases, anthropogenic aerosols and natural forcings (including solar activity and volcanic aerosols) on the changes in subtropical westerly jet and Central Asian precipitation, the researchers adopted the multimodel simulations of 10 models from the Detection and Attribution Model Intercomparison Project.

They demonstrated that the enhanced emission of greenhouse gases could contribute to an equatorial shift of the subtropical westerly jet, while increased Asian pollution and reduced European aerosol emissions can result in a weakened jet, both of which favor the descending motion and drying trend over northern Central Asia in summer since the 1950s.

"Our results show that human-induced emissions of greenhouse gases and aerosols in other regions of the world can also impact Central Asian precipitation and water resources by modulating the key atmospheric circulation," JIANG said.

This work was supported by the Chinese Academy of Sciences and the National Natural Sciences Foundation of China.