Observed trends in the timing of wet and dry season in China and the associated changes in frequency and duration of daily precipitation

An understanding of the changes in precipitation timing, wet days (WD) and duration of extreme wet (dry) spells (WS/DS) is of great significant merit in the management of water resources and agricultural activities. In this study, the spatial features of trends in these precipitation characteristics over China during 1960-2013 were investigated. The timing of wet-/dry-season exhibited significant shift across the whole China. The timings of wet season showed significant delaying trends over the middle and lower Yangtze River basins and earlier onset trends over northern China, with the rate up to 1month per 50-years, which is partly due to the changes in East Asian summer monsoon circulation. Meanwhile, the timings of dry season over the middle and lower Yangtze River basins exhibited prominent earlier trends, combined with the delayed trends of wet season occurrence, resulted in a reduced transition period from wet season to dry season. Accompanying the pronounced shift of the occurrence time of wet-/dry-seasons, WD and duration of extreme WS/DS in wet-/dry-seasons also showed significant change. Predominantly negative trends of wet-season WD largely contributed to the deceasing annual WD in the regions east of 100 degrees E. The shortening of extreme dry-season DS was evident over Northeast China and lower Yangtze River; while the decrease of extreme wet-season WS was observed over the southern China, and these changes may help to reduce the corresponding risk of drought and flood, respectively. Southwest China showed robust less WD and prolonging DS on both annual and seasonal basis, and thus may enhance the risk of drought in this region.