Investigating risk, reliability and return period under the influence of large scale modes, and regional hydrological variability in hydrologic extremes

Due to the present climate change scenario, it is necessary to interpret return period, risk, and reliability of hydrological extremes under non-stationary conditions. The present study aims to understand the crucial design parameters by introducing physically based covariates in the location parameter of the Generalized Extreme Value (GEV) distribution. The analysis is carried out over 30 streamflow gauging stations located across the Godavari River basin, India. To compare the return period, risk and reliability between the stationary and non-stationary conditions, the Expected Waiting Time (EWT) approach is used. The analysis reveals that half of the gauging stations are impacted by large-scale modes/oscillations and regional hydrological variability, primarily by the Indian Summer Monsoon Index (ISMI) and precipitation. The EWT interpretation estimates that the non-stationary return period, risk, and reliability are significantly different from under the stationary condition. Hence, a non-stationary approach can be useful to water managers and policymakers in order to devise sustainable and resilient water resource infrastructure under a climate change scenario.