Inter-decadal shift of spring drought over China around the late 1990s and the possible mechanisms

Based on the Standardized Precipitation-Evapotranspiration Index, this study reveals an inter-decadal shift of spring drought condition in China around the late 1990s, with three significant centers over Southeast China (SEC), the Hetao region (HT), and Northeast China (NEC). Further analysis indicates that potential evapotranspiration (PET) has larger influence on the inter-decadal drought aggravation over HT and SEC than precipitation, while precipitation has a more decisive effect on inter-decadal drought mitigation over NEC than PET. Further analysis suggests that the zonal atmospheric wave train over the Eurasian continent could be responsible for the inter-decadal shift of drought condition over China. The wave train can lead to an anomalous anticyclone around central Asia, which causes significant descending motion over HT and SEC that favors less cloud cover and surface air warming, further resulting in enhanced PET there. Concurrent with the decreased precipitation caused by descending motion and the moisture divergence, the drought in the two regions exhibits inter-decadal aggravation after the late 1990s. Additionally, the anomalous cyclone over Northeast Asia associated with the wave train leads to significant moisture convergence and ascending motion over NEC, resulting in increased precipitation there. The ascending motion also favors more cloud cover and surface air cooling over NEC, thus causing decreased PET there. Therefore, the drought condition over NEC exhibits inter-decadal mitigation after the late 1990s. Further analysis indicates that the Atlantic Multidecadal Oscillation could be an important factor contributing to the inter-decadal shift of drought condition over China by influencing the aforementioned Eurasian wave train.