Study on frequency analysis of regional drought based on ground water depth

Taking ground water depth as a hydrological drought indicator, the drought duration and severity characteristic variables were identified by cumulative frequency approach. The corresponding cumulative frequency of the variation of ground water depth, which suggested the occurrence of drought, was determined based on the statistical analysis of the occurrence of drought in the study region. The reasonability of the drought characteristic variables was illustrated via the relationship of anomalies of the variation of ground water depth and precipitation anomalies. The frequency curve fitting method was adopted to calculate frequency of each drought characteristic variable. Then with GH Copula, the joint distribution of drought duration and severity was constructed and accordingly the drought recurrence periods were estimated. The proposed methods for drought frequency estimation were applied to Dangshan County, Huaibei Plain. The application results show that identified drought events and the corresponding estimated recurrence periods by the GH Copula have high consistency with the actual regional drought circumstances. The presented methods of hydrological drought identified based on the variation of ground water depth of adjacent periods and the recurrence periods calculated by copula, are of clear physical concept. So the methods can be applied to the regions under similar situations.