Observational and supportive modelling analyses of winter precipitation change in China over the last half century

摘要

Overall increasing trends in annual precipitation and widespread warming over China have been documented. During the winter months in southeast China, where snow is commonplace but rarely accumulates, the climatological 0 °C surface isotherm generally defines the southern boundary of the snowfield. Therefore, a warming climate will: (a) modify the southern boundary of the snowfield; and (b) potentially alter the snow-rain ratio. Using recently released daily precipitation from the Asian Precipitation-Highly Resolved Observational Data Integration Towards Evaluation (APHRODITE) and temperature observations from the ERA-40/Interim Reanalyses, this study investigated historical winter precipitation changes in China. Since snowfall observations were largely unavailable for southeast China, snowfall amounts were estimated using a rain-snow threshold temperature (RST) method which was subsequently verified by in situ and satellite observations of snow depth, snow cover, and snow water equivalent (SWE). The composite analysis reveals a decrease in snowfall totals which are accompanied by an increase in rainfall; this change corresponds with the northward retreat of the 0 °C surface isotherm and the snow-rain ratio. Atmospheric circulation analysis indicated lower tropospheric warming with increased moisture over southeast China, consistent with previous studies. Moreover, we observed an increase in the convergence of water vapour flux which sustains the increase in precipitation; this is accompanied by the suppression of snowfall due to the lower tropospheric warming. An additional analysis employed to further substantiate the RST method was undertaken by modelling the snow-rain ratio with the Weather Research and Forecasting (WRF) Model. The results were in agreement with those estimated from the observations.