Threat Assessments on California Rangelands

Percent change in climatic water deficit relative to the 1981-2010 climate period

Example water deficit Map

These maps display the percent change in average climatic water deficit (CWD) from the 1981-2010 climate period to a future climate period for each watershed. Percent change in CWD is provided for two climate projections for each of the three IPCC-SRES scenarios – A1B, A2 and B1. Future climate periods displayed include 2010-2039, 2040-2069 and 2070-2099. Watershed boundaries are from the 8-digit Watershed Boundary Dataset ( CWD is defined as potential evapotranspiration minus actual evapotranspiration. This term effectively integrates the combined effects of solar radiation, evapotranspiration, and air temperature on watershed conditions given available soil moisture derived from precipitation.

Future change in CWD was modeled using the U.S. Geological Survey's Basin Characterization Model (BCM), a regional water balance model (Flint et al. 2013, Flint and Flint, 2012). The BCM was run with two statistically downscaled global climate models (GCMs) (a warm, wet future and a hot, dry future) for each emissions scenario. GCMs included variables for minimum or maximum temperatures, which were considered important determinants of vegetation distribution. Table 1 summarizes the GCMs for each emission scenario.

Table 1. Summary of Global Climate Models (GCMs)

Climate models table

These representative projections were downscaled to 270 meter spatial resolution for monthly estimates of precipitation and maximum and minimum air temperature. The BCM used the downscaled precipitation and temperature as well as elevation, geology, and soils to produce 270 meter-resolution maps of potential evapotranspiration, runoff, recharge, CWD, actual evapotranspiration, sublimation, soil water storage, snowfall, snowpack, snowmelt, and excess water.

Thirty-year water year summaries of CWD were used for this rangelands project. The maps display the percent change in the CWD 30-year average from 1981-2010 to a future CWD 30-year average, averaged by watershed area. Percent change in CWD is calculated as:

ΔCWD = [(CWDx – CWD1981-2010)/ CWD1981-2010]*100


  • ΔCWD = percent change in CWD
  • CWDx = average CWD for climate period x, averaged by watershed area
  • CWD1981-2010 = average CWD for climate period 1981-2010, averaged by watershed area


Flint, L.E., A.L. Flint, J.H. Thorne, and R. Boynton. 2013. Fine-scale hydrologic modeling for regional landscape applications: the California Basin Characterization Model development and performance. Ecological Processes 2:25. Available online at:

Flint, L.E. and Flint A.L. 2012. Downscaling future climate scenarios to fine scales for hydrologic and ecologic modeling and analysis. Ecological Processes 1:2. Available online at: