Hydroclimate of the Spring Mountains and Sheep Range
The U.S. Forest Service, Bureau of Land Management, and U.S. Fish and Wildlife Service are conducting a study to characterize ecological zones in the Spring Mountains and Sheep Range in southern Nevada. The Spring Mountains and Sheep Range are home to some of the most isolated and biologically diverse species and vegetative communities in the Mojave Desert. Higher-elevation communities, often referred to as “sky islands”, are particularly susceptible to the effects of climate change and harbor more than 41 percent of the endemic species in the Mojave Desert ecoregion. Because hydroclimate data are sparse in this area of high topo-climatic variability, USFS and other land management agencies lack sufficient information to understand the relation between hydroclimatic variables and the distribution and productivity of ecological zones, or how ecological zones may be affected by climate change. Ecological zones are large areas with similar environmental conditions which are manifested by characteristic vegetative communities. USGS, as part of this comprehensive study, is characterizing the local hydroclimate emphasizing the magnitude, timing, and distribution of precipitation and evapotranspiration.
Study Publication: SIR 2014-XXXX (in press)
Abstract from SIR 2014-XXXX (in press)
Precipitation, potential evapotranspiration, and actual evapotranspiration often are used to characterize the hydroclimate of a region. Quantification of these parameters in mountainous terrains is difficult because limited access often hampers the collection of representative ground data. To fulfill a need to characterize ecological zones in the Spring Mountains and Sheep Range of southern Nevada, spatially and temporally explicit estimates of these hydroclimatic parameters are determined from remote-sensing and model-based methodologies. Parameter-elevation Regressions on Independent Slopes Model (PRISM) precipitation estimates for this area ranges from about 100 millimeters (mm) in the low elevations of the study area (700 meters [m]) to more than 700 mm in the high elevations of the Spring Mountains (> 2,800 m). The PRISM model underestimates precipitation by 7–15 percent based on a comparison with four high-elevation precipitation gages having more than 20 years of record. Precipitation at 3,000-m elevation is 50 percent greater in the Spring Mountains than in the Sheep Range. The lesser amount of precipitation in the Sheep Range is attributed to partial moisture depletion by the Spring Mountains of eastward-moving, cool-season (October–April) storms. Cool-season storms account for 66–76 percent of annual precipitation. Potential evapotranspiration estimates by the Basin Characterization Model range from about 700 mm in the upper elevations of the Spring Mountains to 1,600 mm in the lower elevations. The model realistically simulates lower potential evapotranspiration on northeast-to-northwest facing slopes compared to adjacent southeast-to-southwest facing slopes. Actual evapotranspiration, estimated using a Moderate Resolution Imaging Spectroradiometer based water-balance model, ranges from about 100 to 600 mm. The magnitude and spatial variation of simulated, actual evapotranspiration was validated by comparison to PRISM precipitation. Estimated groundwater recharge, computed as the residual of precipitation depleted by actual evapotranspiration, is within the range of previous estimates. A climatic water deficit dataset and aridity-index-based climate zones are derived from precipitation and evapotranspiration datasets. Climate zones range from arid in the lower elevations of the study area to humid in small pockets on north- to-northeast facing slopes in the high elevations of the Spring Mountains. Correlative analyses between hydroclimatic variables and mean ecosystem elevations indicate that the climatic water deficit is the best predictor of ecosystem distribution (R2 = 0.92). Computed water balances indicate that substantially more recharge is generated in the Spring Mountains than in the Sheep Range. A geospatial database containing compiled and developed hydroclimatic data and other pertinent information accompanies this report.
Graphs showing relations between mean ecosystem elevations and (A) mean annual precipitation and actual evapotranspiration, and (B) potential evapotranspiration and climatic water deficit, Spring Mountains and Sheep Range, Clark County, Nevada.
Location: southern Nevada
Start Date: 2007
End Date: 2014
Cooperators: U.S. Forest Service
USGS Nevada Water Science Center
160 N. Stephanie St.
Henderson, NV 89074
phone: (702) 564-4625
PRISM: Parameter-elevation Regressions on Independent Slopes Model
USFS: U.S. Forest Service