Investigation and simulations of changes in the relationship of precipitation-runoff in drought years

The frequency and intensity of drought could be increasing with global warming. When drought occurs, the runoff generation process and the precipitation-runoff relationship might change. In this study, the precipitation-runoff relationship in drought years was systematically investigated in the largest freshwater lake basin of China, namely, the Poyang Lake Basin. The results showed that the precipitation-runoff relationship changed significantly (p < 0.05) in drought years. The annual runoff coefficient in drought years decreased by 24.1% compared with that in non-drought years. The decreased magnitude of runoff coefficient had a significant positive relationship (p < 0.01) with the drought severity, i.e., the standardized precipitation index of the year. Two hydrological models calibrated by the objective function Nash-Sutcliffe efficiency significantly overestimated runoff in drought years. Three additional objective functions that are sensitive to low flow simulations significantly improved the accuracy of runoff simulation in drought years. Therefore, we recommend that the selected objective functions for runoff simulation in drought years should be sensitive to low flow simulations. Otherwise, the water resources availability will be overestimated in drought years.