Implications of the Covariation of Soil, Vegetation, and Topography on Soil Moisture Patterns In Two Semiarid Environments

Soil moisture variability is a critical concern for management of training lands, mobility of troops in combat, and detection of land mines and improvised explosive devices. Several studies have examined the individual impacts of soil, vegetation, or topographic variability on patterns of soil moisture, and they have typically found that topography has a stronger influence on soil moisture under wetter conditions. However, for water-limited environments, soil, vegetation, and topographic attributes are often closely connected. We hypothesize that the covariation of these attributes induces a topographic dependence of soil moisture in semiarid climates as well. If confirmed, this dependence would be a valuable tool for soil moisture estimation due to the wide availability of topographic data. To test this hypothesis, we examine soil moisture patterns from two distinct semiarid locations. One location is a high-relief catchment in the foothills of the Front Range in Colorado, where the north-facing slopes are forested and the south-facing slopes are shrublands. Soil analyses indicate that soils on the north-facing slopes are significantly finer than those on the south-facing slopes. In addition, correlations are observed between local soil texture and various topographic indices. Soil moisture patterns are found to be weakly correlated with elevation under wetter conditions and more strongly correlated with aspect-related indices under drier conditions. The other location is in the prairies of southeastern Colorado on the Pinon Canyon Maneuver Site (PCMS) of Fort Carson. In this region, topographic relief is introduced by the widespread occurrence of gullies. Soil moisture was monitored at two sites on PCMS: a gullied site and a comparable ungullied site. Even though the total relief at these sites is quite small, some topographic dependence is also observed here. These results provide clues to the vulnerability of particular locations to erosion, which is expected to benefit sustainable land management efforts.