Regional Frequency Analysis of Extreme Precipitation after Drought Events in the Heihe River Basin, Northwest China

Regional frequency analysis of extreme precipitation after a drought event based on the L-moment method has provided promising insights into drought risk management. The drought index of continuous noneffective rainy days was applied to analyze the droughts with the characteristics of increasing frequency, severity, and duration in the Heihe River Basin. Based on the typical drought records, the precipitation intensity after drought was shown to be greater than the long-term average values. Regional pooling of the precipitation after drought and under normal conditions for 1960-2010 from 14 sites across the Heihe River Basin was applied in a regional frequency analysis based on L-moments to estimate the quantiles for given return-period precipitation events in each of the three homogeneous regions for both the drought and normal series. From the study results, the following observations were made: (1)the Heihe River Basin (14 sites) can be classified into three homogeneous regions by the analysis of discordancy measure and heterogeneity measure. The results of goodness-of-fit measures showed that the Pearson type III (PE3) and generalized extreme value (GEV) distributions were suitable for the basin, but their respective performances for the drought and normal series were clearly different; and (2)the estimated quantiles at a given return period (returnperiod=1, 2, 5, 10, 20, and 50years) for the drought and normal series revealed that the high-intensity precipitation after drought was more than that under normal conditions in all three of the regions. In addition, the spatial variation of extreme precipitation in the drought and normal series was noticeable.