Periodic decadal swings in dry/wet conditions over Central Asia

Abstract

Periodic variability in the hydro-climatic system has important implications not only for climate prediction but also for planning and managing water resources. Here we identify periodic decadal variability of dry/wet conditions in Central Asia (CA) since the mid-20th century, which are tied to the Pacific quasi-decadal oscillation (PQDO) with a period of 8–16 years (r = 0.87). The periodically varying forcing in the Pacific modulates zonal winds and moisture transport and profoundly affects the precipitation on the decadal time scale. The PQDO-related equatorial central Pacific warming significantly heats the overlying troposphere, increasing the meridional temperature/geopotential gradients in the subtropics. As a result, the strengthened westerly jet in CA transports more water vapor from the North Atlantic and increases local precipitation. The plateau to the east further amplifies the increased precipitation in eastern CA through orographic influence on the convection and large-scale circulation. The atmospheric model forced by the PQDO signal reproduces an overall consistent mechanism with the observation, indicating a robust synchronization of the Central Asian hydro-climatic system to the PQDO. The newly discovered oscillatory feature in this study may advance the predictability of Central Asian precipitation on the decadal time scale, which promotes the mitigation and prevention of natural disasters like droughts and wildfires.