Changes in heavy precipitation and floods in the upstream of the Beijiang River basin, South China

The objective of this study was to investigate the changes in heavy precipitation and floods and the causes of flood risk changes in the Beijiang River basin in southern China. Peak flow, daily discharge, and precipitation data from 1969 to 2011 were examined. Trends were calculated using Sen's slope estimator. The statistical significance of the observed trends was checked with the Mann-Kendall method. Change points were detected using the Pettitt test and moving T-test methods. The hydrological periodicity was revealed by wavelet transformation. The results showed that the changes in monthly and monthly maximum 1- and 5-day precipitation and discharges during the flood season showed very similar characteristics. They experienced positive (negative) trends mainly in June-July (April, May, and August), and mostly did not experience significant change points. Compared with the period 1969-1990, monthly and monthly maximum 1(5)-day precipitation and discharges showed increasing (decreasing) trends, mainly in June-July (April-May) in 1991-2011. Overall, the changes in flood risk were mainly influenced by precipitation variability. However, human activity (including urbanization and the construction of reservoirs, soil and water conservation measures, and land use change, among others) have probably affected the flooding process in the study area. The decreases in peak flows during the late 1980s and early 1990s were probably caused by large-scale soil and water conservation measures. Construction of reservoirs in the past 20 years also played a role in the reduction of peak flows. The results of this study are of great scientific value to better understand the changing flood risk under the changing environment in the Beijiang River basin.