Submitted to: Water Resources Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/18/2000
Publication Date: 8/13/2000
Interpretive Summary: The audience of this manuscript is intended to be primarily scientists (hydrologists, ecologists, soil scientists) who are interested in studying the relationships between the atmosphere (i.e., precipitation), vegetation, and soil. Herein, the authors examine how precipitation infiltrates into the soil over the course of many seasons and years. The timing, the amount tand the depth to which water infiltrates into the soil is important in determining what types of vegetation are able to access and utilize this water. In semiarid southeastern Arizona, there tends to be more water infiltrating into the soil (called "recharge") during the winter when the rains are longer lasting and the plants are inactive due to the colder temperatures. This paper attempts to determine how much water was recharged during the winters of 1990-1998, and if this amount is large enough to actually support plants with different rooting patterns.
Technical Abstract: The multiyear, root zone, soil moisture redistribution characteristics in a semiarid rangeland in southeastern Arizona were evaluated to determine the magnitude and variability of deep-profile, wintertime recharge. Intermittent observations from 1990 to 1998 of average volumetric soil moisture under shrub and grass cover showed that significant recharge beyond 0.30 m principally occurs only in the wintertime when the vegetatio is senescent and does not utilize the infiltrating water. Using the physically-based, variably-saturated flow model HYDRUS, wintertime observations were modeled to determine the recharge of soil moisture at different depth intervals in the vadose zone. Simulations with the optimized model indicate that significant recharge of vadose zone does occur well beyond 0.30 m in winter, but that such recharge is highly variable from year to year and appears highly correlated with El Nino episodes. This water could serve as a source of plant water for deeper rooted plants that are active during the subsequent spring season thereby exploiting a niche that the more abundant, shallower-rooted plants, that are active during the summer rainy season, do not.