Nonstationary quantity-duration-frequency (QDF) relationships of lowflow in the source area of the Yellow River basin, China

Study region: The source area of the Yellow River (SAYR) located in the northeastern part of the Qinghai-Tibet Plateau, China Study focus: This study attempts to produce the quantity-duration-frequency (QDF) relationships of lowflow through a nonstationary approach of the generalized extreme value (GEV) models. Detailed derivation of theoretical model of different structures and parameter estimation is presented as the central part, followed by model evaluation and recommendation. Time and two climate indices, i.e., Arctic Oscillation (AO) and Eastern Asia (EA), are selected as covariates. New hydrological insights for the region: For the SAYR, nonstationary GEV models incorporating additional climate-informed covariates show apparent strengths over stationary GEV model. Using AO and EA as covariates, dual-covariate model has not shown apparent advantages over single-covariate model. The introduction of climate indices as critical covariates, in addition to time, is found to be a good choice in the construction of nonstationary GEV models for obtaining the QDF relationships and analyzing multivariate properties of lowflow. The results could help to guide the emergency management and regulation of water resources during the lowflow season, and to assistant the design of water engineering for the future period.