Construction and application of a flood-waterlogging index in the middle and lower reaches of the Yangtze River

In order to objectively identify the regional rainstorm and flood processes and quantitatively assess the intensity of regional rainstorm processes, based on the intensity-duration curve for extreme rainfall, the maximum precipitation intensity within 5 days is regarded as an index to define a flood-waterlogging event and the intensity of regional flood-waterlogging processes. Using the daily precipitation dataset at 502 meteorological stations in the middle and lower reaches of the Yangtze River from 1961 to 2019, the frequency, intensity and variation trend of the regional flood-waterlogging processes in the middle and lower reaches of the Yangtze River are analyzed. The results show that the frequency of the regional waterlogging processes in this region exhibits an increasing trend in recent 60 years. It is obvious that the regional flood-waterlogging processes occur more frequently in the last 20 years, and the proportion of the regional flood-waterlogging processes lasting for 5-9 days to all the waterlogging processes is two-thirds or above. The regional flood-waterlogging days display the spatial distribution of "more in the southern area and less in the northern area" and "decreasing in the northwestern area and increasing in the southeastern area". Moreover, the spatio-temporal variations of the annual precipitation and flood-waterlogging lead to a stronger difference of drought and flood between different areas in this region. The eastern area with more precipitation gets wetter, but the northern and western area with less precipitation gets drier.