Governing Water Futures: Integrating Montana Water Rights into a Hydro-economic Model

Abstract:

Hydrologic impacts of climate change, such as shifts in the quantity and timing of water flows, will compound stress on social-ecological systems, particularly in the arid American West. These shifts can result in loss of aquatic habitat and decreases in aquatic species populations. Additionally, they can impact water dependent economies and livelihoods through the loss or reduction in available water for human consumption, irrigated agriculture, and cultural and recreational activities. Water governance approaches are also a major determinant of future water supplies. Prior appropriation, the foundational water law in the western U.S., is essentially a water distribution policy of ‘first in time, first in right’ where the earliest water users secure and maintain priority use of water sources. Often, water allocation (i.e. legal water rights) data in western states is not linked with climate data and predictive models; given the potential for climate change to disrupt available water supplies, there is a clear need to link climate and water rights data to better understand potential water futures and improve planning. We address this challenge through (1) analysis of a geospatial dataset of Montana surface water rights, and (2) integration of this data into a statewide hydro-economic model that includes a statewide water balance and climate predictions. Further, we explore a case study of Montana instream flow water rights in this platform to determine whether instream flow policies, either in their current or modified form, could serve to balance water use between agriculture and aquatic species habitat protection given the uncertainty of future water availability and timing of flows. By integrating water rights data into a hydro-economic model, we are able to represent physical and legal thresholds of water availability and produce more accurate, meaningful predictions of future water contests. Our results highlight challenges and opportunities for administering water policy and management actions across the state of Montana under a changing climate.