Possible Effects of Human Activities on Trends in Precipitation over the Yangtze River Basin from 1961 to 2016

Increased concentrations of greenhouse gases caused by human activities have been contributing to climate change. The impact of human activity on the spatiotemporal variations in precipitation patterns has been an important focus of study. This paper takes the Yangtze River basin as an example for study. Daily precipitation data observed from 1961 to 2016, and daily precipitation simulation results of using the CAM5.1-1degree model in the International CLIVAR C20C+ Detection and Attribution Project, were used to analyze the contribution of human activities to the spatial, temporal, and trend variations in annual precipitation and three extreme precipitation indices over the Yangtze River basin. Simulation results, which included both anthropogenic and natural influences, were close to observations. Using statistical methods, model simulation ability was tested. It can be concluded that the average result of multiple runs of the actual scenario was more reliable for the simulation of precipitation over the Yangtze River basin. By comparing temporal and spatial variations when accounting for the impact of human activities, average precipitation over the Yangtze River basin showed a decreasing trend when compared with natural forcing only, and this decreasing trend has intensified over time. The increasing trend in extreme precipitation, as affected by human activities, has weakened over time. Based on spatial differences in average precipitation and extreme precipitation trends and percentage anomalies, the areas most affected by human activities were shown to be the upper central and southeast regions and the middle and lower southeast region, all of which showed a decreasing impact. However, in the southwest of the upper Yangtze River, extreme rainfall has increased significantly due to human activity. Increased flood prevention work is recommended for this area. The most significant period for the reduction of average precipitation caused by human activity was 2000-2009, and the sharpest seasonal decreases shown during autumn and winter. The impact of human activities on extreme precipitation was positively correlated with the extreme degree of precipitation. Compared with general heavy precipitation (R90p), extreme heavy precipitation (R99p) was affected by human activities with a greater range and more significant differences in spatial distribution.