Drought evolution characteristics and precipitation intensity changes during alternating dry–wet changes in the Huang–Huai–Hai River basin

摘要

Abrupt drought–flood change events caused by atmospheric circulationanomalies have occurred frequently and widely in recent years, which hascaused great losses and casualties in China. In this paper, we focus oninvestigating whether there will be a rainfall occurrence with higherintensity after a drought period in the Huang–Huai–Hai River basin.Combined with the Chinese climate divisions and the basin's DEM (digitalelevation model), the basin is divided into seven sub-regions by means ofcluster analysis of the basin meteorological stations using theself-organizing map (SOM) neural network method. Based on the dailyprecipitation data of 171 stations for the years 1961–2011, the changes ofdrought times with different magnitudes are analyzed, and the number ofconsecutive days without precipitation is used to identify the droughtmagnitudes. The first precipitation intensity after a drought period isanalyzed with the Pearson-III frequency curve, then the relationship betweenrainfall intensity and different drought magnitudes is observed, as are thechanges of drought times for different years. The results of the studyindicated that the occurrence times of different drought levels show anoverall increasing trend; there is no clear interdecadal change shown, butthe spatial difference is significant. (2) As the drought level increases,the probability of extraordinary rainstorm becomes lower, and the frequencyof occurrence of spatial changes in different precipitation intensities vary.In the areas I and II, as the drought level increases, the occurrencefrequency of different precipitation intensities first shows a decreasingtrend, which becomes an increasing trend when extraordinary drought occurs.In the area III, IV and V, the probability of the different precipitationintensities shows an overall decreasing trend. The areas VI and VII arelocated at the mountains with high altitudes where the variation of differentprecipitation intensities with the increase in drought level is relativelycomplex. (3) As the drought times increase, areas I, II and V, which arelocated on the coastal and in the valley or basin, are vulnerable to extremeprecipitation processes; areas III, IV, VI and VII are located in the inlandarea, where heavier precipitation is not likely to occur. (4) The localrainfall affected by multiple factors is closely related with droughtoccurrence. The characteristics between the first rainfall intensity after adrought period and different drought magnitudes (or drought occurrence times)are preliminarily examined in this paper, but its formation mechanism stillrequires further research.