Watershed and Hillslope Modeling

Nooksack River basin, Whatcom County, WA

Graduate students and I have been modeling the impact landscape changes and climate change on streamflow and mass wasting in watersheds in the Pacific Northwest using the Distributed-Hydrologic-Soils-Vegetation-Model ( DHSVM) developed at the University of Washington and Pacific Northwest National Laboratory. The model simulates a water and energy balance at the pixel scale of a digital elevation model (DEM). It has been applied predominantly to mountainous watersheds in the Pacific Northwest. Our studies are summarized below.

Modeling the Effects of Climate Change on Late Summer Streamflow in the Nooksack River Basin: Ryan Murphy MS Thesis topic (ongoing)

Like many watersheds in the North Cascades Mountain range, streamflow in the Nooksack River is strongly influenced by precipitation and snowmelt in the spring and glacial melt in the warmer summer months. With a maritime climate and a high relief basin with glacial ice (3400 hectares) the streamflow response in the Nooksack is sensitive to increases in temperature, thus forecasting the basins response to future climate is of vital importance for water resources planning purposes. The watershed (2000 sq-km) in the northwest of Washington, USA, is a valuable freshwater resource for regional municipalities, industry, and agriculture, and provides critical habitat for endangered salmon species. Due to a lack of spatially distributed long-term historical weather observations in the basin for downscaling purposes, we apply publically available statistically derived 1/16 degree gridded surface data along with the Distributed Hydrology Soil Vegetation Model (DHSVM; Wigmosta et al., 1992) with newly developed coupled dynamic glacier model (Clarke et al., 2015) to simulate hydrologic processes in the Nooksack River basin. We calibrate and validate the DHSVM to observed glacial mass balance and glacial ice extent as well as to observed daily streamflow and SNOTEL data in the Nooksack basin. For the historical period, we model using a gridded meteorological forcing data set (1950-2010; Livneh et al., 2013). We simulate forecasted climate change impacts, including glacial recession on streamflow, using gridded daily statically downscaled data from global climate models of the CMIP5 with RCP4.5 and RCP8.5 forcing scenarios developed using the multivariate adaptive constructed analogs method (Abatzoglou and Brown, 2011). Preliminary results indicate an increase in winter streamflows due to more rainfall rather than snow, and a decrease in summer flows with a general shift in peak spring flows toward earlier in the spring. Glacier melt contribution to streamflow initially increases throughout the first half of the 21st century and decreases in the latter half after glacier ice volume decreases substantially.

Future work includes how climate change scenarios influence stream temperatures and sedimentation in the three forks. Funding for these projects have been provided by the Nooksack Tribe. Technical support has been provided by researchers at the University of Washington, including Christina Bandaragoda and Chris Frans.

Previous Studies