A Hybrid Index for Characterizing Drought Based on a Nonparametric Kernel Estimator

Abstract

his study develops a nonparametric multivariate drought index, namely, the nonparametric multivariate standardized drought index (NMSDI), by considering the variations of both precipitation and streamflow. Building upon previous efforts in constructing nonparametric multivariate drought index, the nonparametric kernel estimator is used to derive the joint distribution of precipitation and streamflow, thus providing additional insights into drought-index development. The proposed NMSDI is applied in the Wei River basin (WRB), on the basis of which the drought-evolution characteristics are investigated. Three main results were found: 1) In general, NMSDI captures drought onset in a way that is similar to that of the standardized precipitation index and captures drought termination and persistence in a way that is similar to that of the standardized streamflow index. The drought events identified by NMSDI match well with historical drought records in the WRB. Performance is also consistent with that of an existing multivariate standardized drought index at various time scales, confirming the validity of the newly constructed NMSDI in drought detections. 2) An increasing risk of drought has been detected for past decades and will persist to a certain extent in the future in most areas of the WRB. 3) The identified changepoints of annual NMSDI are mainly concentrated in the early 1970s and mid-1990s, coincident with extensive water use and soil conservation practices. In summary, this study highlights a nonparametric multivariable drought index that can efficiently and comprehensively be used for drought detections and predictions.