Using the Basin Characterization Model (BCM) to Estimate Natural Recharge in Indian Wells Valley, California Completed

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The Indian Wells Valley is located in the northern Mojave Desert and it has an arid environment, receiving only 4-6 inches of precipitation annually. Like most desert areas, Indian Wells Valley communities rely mostly on groundwater for their available groundwater supply. Increases in urban and agricultural development have resulted in increased groundwater pumpage for public and agricultural use, causing large water-level declines throughout the valley. The USGS California Basin Characterization Model (BCM) (Flint and others, 2013) was used in a revised form to understand the rate and amounts of natural groundwater recharge in the Indian Wells Valley and to refine historical estimates of groundwater recharge in the valley. Results from this study provide validation of recharge estimates from multiple sources representing parts of the water balance, including variables such as potential and actual evapotranspiration, and streamflow measurements, and are used to evaluate historical and future patterns of natural recharge in the valley.

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Development of a Monthly Dataset of Historical (1981-2010) and 3 Projected Futures (2011-2099) for Climate and Hydrology for Indian Wells Valley, CA

The Indian Wells Valley BCM was developed on a monthly time step at a spatial resolution of 270 square meters (m²) with a model domain that includes the 10 sub-watersheds that surround and drain into the Indian Wells Valley (fig. 1). The BCM used historical climate data from 1981-2010, and 3 future climate projections to develop hydrologic output for the study area such as recharge, runoff, and climatic water deficit. Model inputs include topography, soil properties, and geology datasets, which are static with time; monthly gridded precipitation and temperature datasets; and monthly gridded potential evapotranspiration (PET) (Flint and others, 2013).

The Indian Wells Valley BCM was calibrated to 10 watersheds (table 1) to provide recharge, runoff and climatic water deficit estimates for current and future climate conditions following methods in Flint and others (2013) and Flint and Flint (2012).

Table 2 shows previous estimates of recharge to the principal aquifer of the Indian Wells Valley. The table shows that local calibration results of the BCM model for the time period 1981-2010 correspond very well to previous recorded estimates, providing an independent approach that corroborates the general average annual estimate of approximately 8,700 acre-feet/year.

Future Climate Projections

Three future climate projections were selected from among 20 models used for California’s Fourth Climate Change Assessment for application to Indian Wells Valley. The 3 models chosen are all from the business-as-usual emissions scenario and represent a range in future projected climate conditions from wet to dry. Annual time series of precipitation and average air temperature for the three future climate models are shown in figure 2, illustrating a rise in air temperature for all models of 4-5 degrees C by end of century, and a range of changes in precipitation from +47% to -22%, depending on the model. Climate and hydrologic data for these three future projections are available via web-based download for all sub-watersheds contributing to the principal aquifer in the Indian Wells Valley.