《Tab.1 Critical thresholds of anomaly percentages of runoff Qa in different combinations》

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《干旱致灾临界状态辨识方法》

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A drought that actually occurred in the region in 2015is selected as an example to illustrate the process of applying the above critical plane for drought warning.According to the above sample selection method，the drought samples are selected，and a potential drought event from July 5，2015to August 3，2015is detected.The five characteristic indexes D，Pa，Qa，E珚，and Qminare calculated daily from July 5and are transformed into aggregative indexes according to Eqs.（11）-（13）.Fig.3presents the daily sample points and critical planes corresponding to the aggregative indexes.The size of the points in the figure gradually goes up with time.Based on this，the development process of this drought can be intuitively observed，namely the process of the sample points moving away from the beginning to gradually approaching and finally crossing the critical state plane and transforming into a disaster-causing state.It is consistent with the record in the yearbook of\""phased low rainfall and summer droughts occurs from July to August；precipitation continues to be low；some areas are plagued by moderate summer droughts\"".Among them，the critical disaster happened on July 13，2015.The corresponding changes in the drought indexes are shown in Fig.4.Before July 13，the changes in the anomaly percentages of precipitation and runoff are relatively stable，with a decrease of about 90%and 40%respectively over the same period of the previous year，but the duration is relatively short，and the minimum low water flow is still relatively high，and it is not yet a disaster.After that，the number of invalid rainfall days rises，the evaporation surges，and the runoff anomaly continues to decrease.Although the anomaly percentage of precipitation has risen，it is still 60%-90%less than those in the same period in the previous years，triggering disasters.