Does Rapid Urbanization Trigger Significant Increase of Cumulative Heavy Rains in China?

Severe disasters caused by extreme precipitation events have attracted more and more attention. The relationship between climate change and extreme precipitation has become the hottest scientific frontier issue. The study of daily torrential rain observations from 659 meteorological stations in China from 1951 to 2010 shows that rapid urbanization may have triggered a significant increase in heavy rains in China. It reached following conclusions: China's interdecadal heavy rainfall amount, rainy days and rain intensity increased significantly, with an increase of 68.71%, 60.15% and 11.52%, respectively. The increase in the number of stations was 84.22%, 84.22% and 54.48%, respectively. It showed time change of “rapid - slow - rapid increase” and spatial change of gradual increase from southeastern coast to central China, southwest, north China, and northeastern regions. Rapid urbanization factors, including secondary industry output (GDP2), urban population ratio (UP), annual average haze days (HD), are likely to be the main causes of the increase in heavy rains in China. Their explanations of the variance of heavy rainfall amount (HRA), rainy day (RD) and rain intensity (RI) in China reached 61.54%, 58.48% and 65.54%, respectively, of which only the explanation of variance of heavy rainfall amount, rainy days and rain intensity was as high as 25.93%, 22.98% and 26.64%, respectively. However, explanation of variance of climatic factors including WPSH (West Pacific Subtropical High), ENSO (El Niño–Southern Oscillation) AMO (Atlantic Interdecadal Oscillation), and AAO (Antarctic Oscillation) was only 24.30%, 26.23%, and 21.92%, respectively. Compared with the rapid urbanization forcing factor, the impact of these climatic factors was only one third of the former. The panel data of China's county-level total population and annual average of visibility days were significantly correlated with China's interdecadal heavy rainfall amount, rainy days and rain intensity. Their spatial correlation coefficient increased gradually from 1951-1960 to 2001-2010, that is, the total population of the county level increased from 0.35, 0.36, and 0.40 to 0.54, 0.55, and 0.58, respectively. The annual average of visibility days increased from 0.36, 0.38, and 0.48 to 0.55. 0.57, 0.58, further indicating that rapid urbanization triggered a significant increase in interdecadal large-area heavy rains in China.