Abstract. Model-based risk assessment of hydrological extremes needs to consider the interactions between the many stakeholders in a river basin as well as the institutions and regulations that mediate them. Unfortunately, commonly employed representations of human-operated structures in hydrological models are limited in their ability to capture human-mediated coordination and control actions in complex river basin systems. This study contributes a detailed diagnostic analysis of the parametric controls and their effects in standard reservoir representations in flood and drought modeling. Our diagnostic analysis uses the Water Balance Model (WBM), which features detailed representations of the human infrastructure coupled to the natural processes that shape water balance dynamics. Our analysis focuses on challenges posed by human-mediated coordination and control actions using the multi-reservoir cascade of the Upper Snake River Basin (USRB) in the Western U.S. We employ a time-varying sensitivity analysis that utilizes Method of Morris factor screening to quantify how the parametrizations of the reservoir release rules impact modeled flows throughout the USRB. Our results demonstrate the importance of understanding the state-space context in which reservoir releases occur and where operational coordination plays a crucial role in avoiding or mitigating water-related extremes. Understanding how major infrastructure is coordinated and controlled in major river basins is essential to properly assessing future flood and drought hazards in a changing world. This implies that the validation of hydrological models for this purpose should move beyond the usual goodness-of-fit checks of outlet flows to incorporate an assessment of the actual emergency response operations used to mitigate hydrological extremes.
