Overview:
The model of watershed hydrology and water management used for the Lower Nooksack Water Budget is Topnet-WM, developed for Water Resources Inventory Area 1 (WRIA 1) in an effort led by researchers from Utah State University, as reported in peer-reviewed publications (Bandaragoda et al., 2004; Ibbitt and Woods, 2004; Tarboton, 2007). The model has also been applied, at finer spatial resolution, to the Fishtrap Creek and Bertrand Creek watersheds (Bandaragoda, 2008; Bandaragoda and Greenberg, 2009). The model processes of Topnet-WM are described in detail in Chapter 2 Model Processes. The daily meteorological variables required by Topnet-WM are precipitation, temperature (minimum and maximum), and wind speed.

Prior to the Lower Nooksack Water Budget project, WRIA 1 Topnet-WM used interpolated climate data (1946-2006) from 19 weather stations located within or near the WRIA 1 boundary. A significant component of the Lower Nooksack Water Budget Project was to update Topnet-WM to use the high resolution (1/8 lat/long degree; approximately one data point every 8 miles) gridded climate dataset that is updated and distributed, on an ongoing basis, by the University of Washington (UW) Land Surface Hydrology Research Group1 , following methods described in Maurer et. al. (2002) and Hamlet and Lettenmaier (2005). This dataset includes daily precipitation, wind speed, and daily maximum and minimum temperatures over the 1915 through 2011 water years (October 1 through September 30).

Figure 1 shows the distribution of the updated mean annual precipitation distribution derived from the Lower Nooksack Water Budget Topnet-WM gridded climate data for the 172 drainages (black dots) in WRIA 1. The lowest annual precipitation values are around Lummi Island and Bellingham (31-38 inches per year) and the highest precipitation values are near Mount Baker (121-207 inches per year). The increase in annual precipitation follows a gradient of increase from the west coast of the watershed to the eastern mountains, reflecting the role of orographic uplift of moist oceanic air masses in generating precipitation in this region.

Purpose:
The purpose for updating climate data used for watershed model inputs is to use the most current and up to date datasets. For the Lower Nooksack Water Budget Topnet-WM model, this includes new Snotel stations, an additional 8 years of daily climate data, and a higher resolution data product, compared to the initially developed Topnet-WM (Tarboton, 2007), which was populated with climate data ending in 2004. Updated climate data helps build our knowledge of the watershed system, since we have more information about when and where water is input to the system as rain and/or snow.

This resource is a subset of the Lower Nooksack Water Budget (LNWB) Collection Resource.