Central Asia is a semiarid to arid region that is sensitive to hydrological changes. We use the Community Atmosphere Model version 5 (CAM5), equipped with a water tagging capability, to investigate the major moisture sources for climatological precipitation and its long-term trends over Central Asia. Europe, the North Atlantic and local evaporation, which explain 33.2±1.5%, 23.0±2.5% and 19.4±2.2% of the precipitation, respectively, are identified as the most dominant moisture sources for northern Central Asia (NCA). For precipitation over southern Central Asia (SCA), Europe, the North Atlantic and local evaporation contribute 25.4±2.7%, 18.0±1.7% and 14.7±1.9%, respectively. In addition, the contributions of South Asia (8.6±1.7%) and the Indian Ocean (9.5±2.0%) are also substantial for SCA. Modulated by the seasonal meridional shift in the subtropical westerly jet, moisture originating from low- and midlatitude is important in winter, spring and autumn, while northern Europe contributes more to summer precipitation. We also explain the observed drying trends over southeastern Central Asia in spring and over NCA in summer during 1956-2005. The drying trend over southeastern Central Asia in spring is mainly due to the decrease in local evaporation and weakened moisture fluxes from the Arabian Peninsula and Arabian Sea associated with the warming of the western Pacific. The drying trend over NCA in summer can be attributed to the decrease in local evaporation and reduced moisture from northern Europe due to the southward shift of the subtropical westerly jet.