Combined characteristics of drought on multiple time scales in Huang-Huai-Hai River basin

In order to provide basis for the partition of drought, combined characteristics of drought on multiple time scales in Huang-Huai-Hai River basin were analyzed by Standardized Precipitation Index (SPI) based on the daily precipitation data of 203 meteorological stations covering 1961–2013 period. The results of the study indicate the following: (1) Annual drought characteristic—the analysis indicates more frequent drought events in this basin at frequency of 26.4 %. Drought intensity and drought site percentage show an increasing trend at tendency rate of −0.11 and 0.93/decade. The highest SPI value of −2.27 and the largest drought site percentage of 71.9 % are observed in 1997. Drought often occurs in continuous 2 or 3 years that usually leads to dire consequence on agriculture and the national economy such as during 1965–1966, 1980–1982, and 2001–2002. (2) Seasonal drought characteristic—autumn has the highest drought frequency of 32.1 %, and spring has the lowest drought frequency of 24.5 %. Drought intensity in spring, summer, and autumn shows an increasing trend, while winter drought intensity shows a decreasing trend. Drought site percentage of autumn shows an increasing trend, but drought site percentage of spring, summer, and winter shows a decreasing tendency. The basin often experiences seasonal continuous drought. Especially the summer–autumn drought has the highest frequency and the expanding trend of drought site percentage. Continuous droughts of three seasons are also frequent such as in the years 1965, 1967, 1995, and 2001. (3) Monthly drought characteristic—November has the highest drought frequency of 34 % and expanding trend of the drought intensity and drought site percentage. The lowest drought frequency of 28.3 % is in March, July, and August. In January, drought intensity shows decreasing trend, but drought site percentage shows an increasing trend. In March, April, and from July to November, the drought intensity and drought site percentage show an increasing tendency. While in February, May, June, and December, the drought intensity and drought site percentage show a decreasing tendency.