Human activities impact the propagation from meteorological to hydrological drought in the Yellow River Basin, China

Quantifying the role of human activities in the process of drought propagation from meteorological drought to hydrological drought is helpful in developing mitigation strategies and in prediction of hydrological drought. To quantify the role of human activities, we compared the results from using simulated natural and observed streamflow to calculate drought indices and drought propagation time. In addition, we compared different propagation detection methods for evaluating the spatiotemporal characteristics of drought propagation from meteorological to hydrological in the Yellow River Basin during the period 1962-2018. The results show: (1) The intensity of meteorological drought (characterized by the standardized precipitation evapotranspiration index) in upstream regions showed an upward trend on the short-term (1-month) scale. At the 6-month scale, human activities reduced hydrological drought events (characterized by the standardized streamflow index) at 93% of stations in the midstream and downstream reaches. (2) The proposed center of gravity method is more suitable for calculating the propagation time after the impact of human activities, while the onset method is suitable for early drought warning. (3) Human activities shortened the propagation time for the controlled area of about 58% of stations (11 out of 19) during the growing season and prolonged it for the controlled area of about 53% of stations (10 out of 19) during the nongrowing season in the Yellow River Basin.