Water resources planning has long been challenged by the presence of deep uncertainty in how hydroclimatic and societal factors will evolve. Deep uncertainty is especially present in how individual and collective human preference and action are represented in water resources systems models. Modeling human action is challenging enough when considering historical conditions but becomes most confounding when envisioning human response to previously unexperienced conditions, such as longer droughts or higher temperatures. Bottom-up planning frameworks attempt to overcome this challenge by employing exploratory modeling, which assesses a system under a broad range of plausible states of the world. In this study, we expand on prior work in the Upper Colorado River Basin within the state of Colorado by applying such a bottom-up framework to the individual irrigation demands of hundreds of agricultural water users.

The basin supports water supply for several sectors, cities, towns and individuals who vie for water through the doctrine of prior appropriation. Water users in the basin have been adapting to increasingly stressed and uncertain conditions by applying conservation measures, and committing to formal or informal water right trading agreements. Through this exploratory modeling approach, we are able to represent hundreds of adaptive demand decisions for irrigation users in this basin, that vary by their hydrologic condition triggers, demand adjustment levels and the number of users that employ them. These adaptive demands are unique to each user and dynamically change under a large ensemble of hydroclimatic conditions, creating a total of 600,000 so-called “states of the world” for this basin. Through this experiment we explore the capacity (and the limits) of adaptive irrigation demand management through informal water transfers to modulate the effects of drought conditions on the basin’s multisectoral water users both individually and collectively. Our findings can inform water conservation policy, as well as support the establishment of more formal trading mechanisms in the basin and across the state of Colorado.