Precipitation Trends Over Mainland China From 1961–2016 After Removal of Measurement Biases

Abstract

Following the removal of measurement biases from daily observed gauge records for the period 1961–2016 at 2,250 national stations over mainland China, the precipitation trends and causes were analyzed. Measured annual precipitation trends have been overestimated to varying degrees in most regions, with the exceptions of Northwest China and northern Tibet. On average, the annual precipitation trend over mainland China decreased from 3.98 to 2.04 mm/10 yr after bias adjustment. The dramatically precipitation-increasing (wetting) zones in Northeast China and the lower reaches of the Yangtze River were found to be disappearing at a faster rate than what we observed. Meanwhile, the extent of markedly precipitation-decreasing (drying) zones in the Yellow River Basin shrank more slowly than what was indicated by measured records. Adjusted annual light rain amounts exhibited a weaker increasing trend over mainland China; conversely, adjusted annual rainstorm amounts displayed stronger increasing trends than reported previously. The changes of trace precipitation days, precipitation days, mean wind speed on precipitation days, and observed precipitation amount comprehensively affected the trends of bias-removed precipitation. The declines in measured wind speed and precipitation amount resulted in accelerated reductions in adjusted precipitation over Southwest and North China. In Southeast China, the increasing trend of bias-adjusted precipitation was smaller than that indicated by original data due to the reduction in mean wind speed when precipitation occurred. In Northwest China and northern Tibet, however, the increases in measured precipitation amount and precipitation days mutually led to larger increasing trends in the adjusted data.