Climatic trend analysis of consecutive rainfall events in spring over Three Gorges Reservoir Area

The consecutive rainfall event (CRE) is an important trigger to geologic hazards like landslide and collapse, which are potential risk factors for the safety of the Three Gorges Reservoir. Based on the daily precipitation dataset from 1960 to 2015, the spatial-temporal distribution and the trend of the CREs occurring in the Three Gorges Reservoir Area in spring are investigated. The results show that:(1) the occurrence frequency and duration days of the CREs exhibit regional differences, with a greater occurrence frequency and a longer duration for the CREs in the southern than those in the northern regions. The occurrence frequency and the duration of CREs as well as the precipitation have exhibited a trend of decrease in recent 56 years. The precipitation intensity slightly enhanced and the interannual variability of CREs is evident. (2) The CREs are classified into three categories, i.e., the short-termed done with the duration of 5 to 6 days, the medium-termed with the duration of 7 to 10 days and the long-termed with the duration of 11 days and beyond, and the spatial-temporal distribution and the trend of these CRE sub-categories are further compared. The results suggest that the occurrence frequency, duration and precipitation of the short-termed CREs have increased slightly. In comparison, these feature variables in the medium-termed and the long-termed have decreased, particularly for the latter, because none has occurred since year 2000. (3) The trend of the ratio of precipitation of CREs to the total precipitation in spring is analyzed and the results suggested a decrease trend. In addition, the ratio of the transient rainfall with the duration less than 5 days has increased. (4) Specially, the long-termed sub-category dominates the reduction trend in the southern region, whereas the short-termed and the medium-termed play a major role for the reduction in the northern region. (5) The event accumulated precipitation is determined by the duration. In spite of such a reduction trend of CREs, which have shown some new features in the last 10 years, such as the increase in the occurrence frequency, precipitation intensity and interannual variability of the CREs have been found evident, particularly in the southeastern region. This implies an increased risk of the geological hazards, and thus deserves more attentions.