A Non-stationary Standardized Streamflow Index for hydrological drought using climate and human-induced indices as covariates

Abstract

The aim of this paper is to propose a new non-stationarity hydrological drought index, which incorporates the climate-driven and human-induced non-stationarities in streamflow. For this purpose, significant teleconnection indices have been selected by correlation analysis to represent large-scale climate variability, and human-induced indices have been calculated using the Soil and Water Assessment Tool (SWAT) to indicate varying anthropogenic forcing. Whereafter, a non-stationary probability model fitted to streamflow series has been developed using the climate-driven and human-induced indices as covariates. Base on the non-stationary model, we present a variation of the classical Standardized Streamflow Index (SSI), named Non-stationary Standardized Streamflow Index (NSSI). Focusing on the streamflow records of Luanhe River basin from 1958 to 2011, a comparison of performance between NSSI and SSI has been conducted to demonstrate the capability of the NSSI. Finally temporal-spatial patterns of drought during the last 40 years over the basin have been estimated by using the NSSI. The results show that the non-stationary model describes the variability of streamflow better than a stationary one, and the covariates selected with Akaike information criterion (AIC) provide insights into non-stationary behaviors. Since the NSSI effectively accounts for the non-stationarities of streamflow associated with climate changes and human activities, it provides more reasonable and satisfactory results than the SSI. Additionally, it is indicated that serious long-term droughts generally appeared more frequently in the southeast of Luanhe River basin, and an obvious aggravating tendency of drought was observed in this area during 1971–2011. The presented NSSI enables hydrological droughts to be better characterized in a non-stationary context, thus providing valuable references for the improvement of drought index and the drought related policy-making.