Modeling climate change impacts to Rocky Mountain headwater hydrology

Abstract

Rocky Mountain headwater catchments provide 85% of Colorado River streamflow and also feed the large Arkansas and Platte River basins. The continued growth of cities from California to Arkansas depends on reliable export from these topographically complex basins. Despite consensus that high-elevation headwaters are more sensitive to climate warming, most models used to predict climate impacts to downstream basins are known to perform poorly in these regions. Here we use an integrated model to better understand the main hydrological drivers of hydrology that are affected by increases in temperature in mountain regions- shifts from snow to rain and increases in energy, finding that energy budget changes dominate impacts to streamflow export. We present a new method to develop scale-effective parameterizations of hydraulic conductivity in topographically complex regions for use in integrated modeling applications that are limited by computational demand. Finally, we compare climate impact predictions across modeling resolutions to understand the limitations of coarse-resolution, simplified models to predict streamflow export from Rocky Mountain headwaters. Our results highlight the importance of idealized model experiments and model development to understand headwater hydrology in a future climate. Furthermore, they suggest that the models used currently may underestimate climate-induced reductions to streamflow generated in the Rocky Mountains.