Spatio-temporal characteristics and possible mechanisms of rainy season precipitation in Poyang Lake Basin, China

Anomalous precipitation during the rainy season (April-June) exerts a considerable impact on hydro-climatic processes in the Poyang Lake Basin (PLB), China. In this study, the spatial and temporal patterns of rainy season precipitation from 1960 to 2014 were investigated using principal component analysis. Possible associations of rainy season precipitation with Nino-3.4 sea surface temperature (SST), maximum consecutive 5 d precipitation amount (RX5day), and diurnal temperature range (DTR) were explored through linear regression analysis. The possible water vapor flux mechanisms for the rainy seasons in dry/wet years were also investigated. The primary spatial pattern indicated a common variation trend in rainy season precipitation, and the variability in maximum value of this, occurring around 28 degrees N, decreased to the north and to the south. The corresponding time series of the primary spatial pattern implied that northern parts were more vulnerable to drought and flood than other parts of the basin. The secondary spatial pattern indicated a north-south dipole, and the corresponding time series showed strong interannual variability. The results also showed that Nino-3.4 SST in winter may positively impact the subsequent year's rainy season precipitation. Strongly positive correlation existed between RX5day and rainy season precipitation, but the correlation between DTR and rainy season precipitation was negative. Further, the water vapor transport from western boundaries into the PLB was substantial, whereas across the eastern boundary there was mainly an output of water vapor. Large input/output values were concentrated at about 850 hPa. Composite analysis indicated that a sizeable quantity of water vapor converged over the basin in wet years, forming effective precipitation with negative values of divergence over the PLB. For dry years, positive anomalies in water vapor flux divergence implied that little water vapor had converged over the basin.