Water resources systems models enable valuable inferences on
consequential system stressors by representing both the geophysical
processes determining the movement of water, and the human elements
distributing it to its various competing uses. This study contributes a
diagnostic evaluation framework that pairs exploratory modeling with
global sensitivity analysis to enhance our ability to make inferences on
water scarcity vulnerabilities in institutionally complex river basins.
Diagnostic evaluation of models representing institutionally complex
river basins with many stakeholders poses significant challenges. First,
it needs to exploit a large and diverse suite of simulations to capture
important human-natural system interactions as well as
institutionally-aware behavioral mechanisms. Second, it needs to have
performance metrics that are consequential and draw on decision-relevant
model outputs that adequately capture the multi-sector concerns that
emerge from diverse basin stakeholders. We demonstrate the proposed
model diagnostic framework by evaluating how potential interactions
between changing hydrologic conditions and human demands influence the
frequencies and durations of water shortages of varying magnitudes
experienced by hundreds of users in a sub-basin of the Colorado river.
We show that the dominant factors shaping these effects vary both across
users and, for an individual user, across percentiles of shortage
magnitude. These differences hold even for users sharing diversion
locations, demand levels or water right seniority. Our findings
underline the importance of detailed institutional representation for
such basins, as institutions strongly shape how dominant factors of
stakeholder vulnerabilities propagate through the complex network of
users.