Using Field-Informed Hydrologic Modeling to Understand Species-specific Plant Water Stress under Differing Climate Scenarios

Abstract

The Upper Colorado River Basin (UCRB) supplies water to nearly 40 million people, but is experiencing unprecedented drought due to climate change. Terrestrial water flux largely depends on evapotranspiration (ET), which is heavily linked to plant water stress. Thus, studying plant water stress is an important way to understand the future state of drought in the UCRB.

Snodgrass Hillslope, located in the East River Watershed, is a well-studied and representative headwater catchment for the UCRB. A two-month field campaign here included collection of atmospheric data from meteorological towers, daily soil moisture measurements, vegetation parameters, and infiltration rates. To situate these observations into the larger context of climate change and drought, we incorporate them into ParFlow-CLM, an integrated hydrology and land surface model, to examine water stress under different climate scenarios for forb and shrub species. ParFlow-CLM typically utilizes International Geosphere-Biosphere Programme (IGBP) land cover classes, but by altering the vegetative parameters within these classes, we are able to more specifically account for plant species recorded at our field site. Beginning with a baseline simulation, we initiate ParFlow-CLM with vegetation parameters, soil properties, and atmospheric forcing. We then manually alter additional parameters to match the observed soil moisture data. Once the baseline model results are validated with soil moisture measurements, we subsequently manipulate atmospheric forcings, increasing temperature, changing rainfall patterns, and adjusting initial snowpack to simulate climate change. We study the effects of these manipulations in a single-column, single-species model.

Model results will allow us to better grasp how climate change scenarios might affect the vitality of shrubs as compared to forbs, as well as invasive species as compared to native species. The work also inquires how vegetative shifts might impact the water balance downstream, inter-species ecological interactions, and the local wildflower tourist economy.