Spatial and temporal patterns of precipitation variability over mainland China: III: causes for recent trends

A few of features of long-term precipitation changes have been reported for mainland China for the last decades. The understanding of causes for the observed precipitation trends, however, is lacking. This paper comprehensively analyzes the long-term changes of multi-indicators of precipitation and atmospheric moisture over mainland China, the paleo-precipitation variations over representative areas, and the previous studies related to observed changes and possible causes of precipitation. The following conclusions are drawn: ① There is an obvious regional difference of recent precipitation trends in the country, but no significant long-term change is detectable over the past century or decades for mainland China on a whole. Frequency and amount of intense precipitation or rainstorms appear to increase over the last decades, and frequency of light rain events especially the trace rain events experiences a highly significant decrease over the same time period. ② Reanalysis data (NCEP/NCAR and ERA-Interim) shows a general increase in atmospheric moisture net budget over the last 3 decades, and sounding data and surface observations show significant upward trends of atmospheric perceptible water or specific humidity over the last decades. Tree-ring data and historical documental records indicate that the recent changes of precipitation are well within the ranges of historical natural variability, except for northeastern part of the Qinghai-Tibetan Plateau where the annual precipitation of the last century reconstructed based on tree-ring data seems to surpass the averages of any single century over the last ten centuries. ③ Instrumental observations of the last century show a distinct characteristic of multi-scale quasi-periodicals for annual total precipitation in the North China Plain, with each of them corresponding to the recognized variations of external forcings or internal modes of climate system, indicating the possible influence of natural forcings and variability on precipitation. The influence of increased atmospheric greenhouse gas concentration on precipitation in mainland China on a whole or in the eastern monsoon region of the country can hardly be detected, though the precipitation changes of Northwest China based on proxy data, instrumental data and modeling data are generally consistent with the theory expectation. (4) Weakening of regional surface wind speed is causing a systematic bias in observations of precipitation, and this is very likely to have led to, at least partially, a false upward trend of northern winter snowfall and annual intense precipitation frequency through increasing the catch-rate of rain gauges. The rising level of aerosols concentration in atmosphere is likely to be another major reason for the upward trend of intense precipitation frequency, and it is very likely to be one of the most important causes for the wide-spread decline of light and trace rain events in the monsoon region. ⑤ The data biases of the current observational data related to urbanization effects very likely account for an additionally substantial part of the reported increase in short-duration intense precipitation frequency and amount, and also for a large part of the observed decline of light and trace rain frequency in eastern monsoon region of the country. © 2016, Editorial Board of Advances in Water Science. All right reserved.