The high level of dependence upon groundwater in the American Southwest has led to the rapid depletion of those resources. Future population and economic pressures will force further increases in the extraction of groundwater, perhaps at the expense of the economic well-being of the region. Recent studies support the probability of diffuse precipitation recharge but none have quantified it on a long-term basis. The objective of this study was to verify the possibility of significant quantities of diffuse precipitation recharge.

One hundred years of actual precipitation data from near Las Cruces, New Mexico were used as input to a one-dimensional numerical model to explore this concept. Four soil textures (two sandy loams, a loamy fine sand, and a clay) were simulated in soil profiles, some two, some six meters deep, both barren and vegetated. Barren loamy fine sand showed continuous recharge throughout the evaluated time period. This decreased to five major periods of possibly substantial recharge when vegetation was simulated. Barren and vegetated sandy loam soils both displayed recharge during these five periods. Sandy loam and even clay soils showed localized recharge under ponded conditions as if enhanced by surface runoff.

Climate conditions supporting the initiation of recharge include both single, very large rainfall events and gradual soil moisture content increases. Recharge periods ended if two consecutive years had below average rainfall. El Ni¤o conditions didn’t correlate well with the five recharge periods, but Eastern Pacific cyclones were responsible for the two single, largest rainfall events, both of which initiated major recharge periods and may be responsible for the perpetuation of other periods as well.