Hydrological drought indexing approach in response to climate and anthropogenic activities

A revisited hydrological drought analysis is necessary for a human-modified period where human activities in addition to natural processes can influence runoff. Hence, a new drought indexing approach (NDIA) is proposed for indexing hydrological drought in response to climatic and anthropogenic contributions. The NDIA involves three main components, namely, trend and change-point analysis, the estimation of runoff variability induced by climate and human activities, and indexing steps. The current study showed that during the study period (1983-2012), with a change point in approximately 1997-1998, 3.16% and 0.93% decreases in the annual average runoff and precipitation, respectively, with an insignificant increase in potential evapotranspiration, were observed from period 1 (1983-1997) to period 2 (1998-2012). The hydrological analysis showed that climatic and land use changes contributed 69.4% and 30.6%, respectively, to mean runoff variability, which indicated the need to consider human contributions in drought analysis during the disturbed period (1998-2012). Hence, using the proposed hydrological drought indexing process in the disturbed period, human-induced drought (HID) and climate-induced drought (CID) were individually estimated. The analysis showed that the duration of HID was less than that of CID, but the number of events was high. The findings were also cross-compared with basin development information and land use classification using a geographic information system (GIS), and this cross-comparison confirmed human intervention during the disturbed period. Based on the overall results, it was concluded that anthropogenic intrusions altered the hydrological time series and instigated or alleviated drought events in the Anthropocene.