Quantifying the Interaction between Landscape and Climate on Water Resources

Growing populations and a changing climate result in increasing stress on water resources in the western United States. Planning for future population and climate conditions requires an evaluation of watershed response to changes in climate. While it is an oversimplification to assume a similar response throughout all watersheds, it is also impractical to study the complex hydrologic response of every watershed in depth. To address this challenge we quantify the connection between landscape characteristics and differential sensitivity of watersheds to climate change. We compare over 100 years of historical hydrologic data from seven seasonally snow-dominated watersheds near Salt Lake City, Utah. Mean annual precipitation (790 mm - 1290 mm) and temperature (3.3°C - 6.9°C) differ primarily as a function of watershed elevation. Mean annual streamflow, normalized by watershed area, (150 mm to 820 mm) differs primarily as a function of mean precipitation. Due to the close proximity of the watersheds, precipitation and temperature exhibit similar inter-annual variability. However, due to unique landscape characteristics of the watersheds, streamflow values exhibit large differences in inter-annual variability between the watersheds and the mean annual water yield ranges from 0.18 to 0.63. We investigate the processes controlling inter-annual streamflow in order to quantify the influence of climate and landscape on hydrologic partitioning. Inter-annual variability in precipitation explains between 47%-73% of the annual variability in streamflow. Surprisingly, the remaining variability is not correlated to annual or seasonal temperature. Instead, inter-annual variability in subsurface storage and the rate of snowmelt further reduce the uncertainty in annual streamflow. Together, precipitation, storage, and snowmelt rate explain nearly all (85%-96%) of the annual variability in streamflow. Storage accounts for a legacy effect of past climate on streamflow that varies between watersheds based on subsurface characteristics. A faster snowmelt reduces the ability of the water to infiltrate deep into the subsurface, resulting in increased streamflow. The rate of snowmelt is primarily controlled by solar radiation and varies between watersheds based on hillslope shading characteristics. These controls on hydrologic partitioning indicate that subsurface and topographic characteristics control the differential sensitivity of watersheds to changes in climate