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Abstract Hydrologic connectivity refers to the processes and thresholds leading to water transport across a landscape. In dryland ecosystems, runoff production is mediated by the arrangement of vegetation and bare soil patches on hillslopes and the properties of ephemeral channels. In this study, we used runoff measurements at multiple scales in a small (4.67 ha) mixed shrubland catchment of the Chihuahuan Desert to identify controls on and thresholds of hillslope‐channel connectivity. By relating short‐ and long‐term hydrologic records, we also addressed whether observed changes in outlet discharge since 1977 were linked to modifications in hydrologic connectivity. Hillslope runoff production was controlled by the maximum rainfall intensity occurring in a 30‐min interval (I30), with small‐to‐negligible effects of antecedent surface soil moisture, vegetation cover, or slope aspect. AnI30threshold of nearly 10 mm/h activated runoff propagation from the shrubland hillslopes and through the main ephemeral channel, whereas anI30threshold of about 16 mm/h was required for discharge from the catchment outlet. Since storms rarely exceedI30, full hillslope‐channel connectivity occurs infrequently in the mixed shrubland, leading to <2% of the annual precipitation being converted into outlet discharge. Progressive decreases in outlet discharge since 1977 could not be explained by variations in precipitation metrics, includingI30, or the process of woody plant encroachment. Instead, channel modifications from the buildup of sediment behind measurement flumes may have increased transmission losses and reduced outlet discharge. Thus, alterations in channel properties can play an important role in the long‐term (45‐year) variations of rainfall–runoff dynamics of small desert catchments.
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Landscape Position Impacts on the Water Balance in the Chihuahuan Desert: Insights From Cosmic-Ray Neutron Sensing at Upland Watershed and Downstream Playa Sites
In the semiarid, water-limited deserts of the Southwest United States, soil moisture is a crucial factor influencing atmospheric, hydrologic, and ecological processes. These dynamics are driven by infrequent yet significant precipitation events that redistribute moisture and establish hydrologic connectivity across the landscape. The Chihuahuan Desert, particularly within its endorheic basins, exemplifies these large-scale interactions where a complex balance of hydrological fluxes is maintained within a closed system. These basins receive most of their precipitation in upland regions, from which surface runoff can lead to downstream connectivity. This connectivity is influenced by the local water balance, including interactions among precipitation, leakage, and evapotranspiration, which are essential for understanding soil moisture variability. Additionally, soil moisture is affected by soil profile characteristics, vegetation, and atmospheric conditions. Field-scale methods like Cosmic-Ray Neutron Sensing (CRNS) are more appropriate than point-scale in situ sensors for quantifying hydrologic connectivity between upland and downstream regions, as CRNS reliably captures soil moisture temporal dynamics over several hectares. This study examines these dynamics within the endorheic Jornada Basin of the Chihuahuan Desert, focusing on two contrasting sites: an Upland Watershed (UW) on a piedmont slope and a Downstream Playa (DP) in a valley bottom. Using CRNS and complementary water balance instrumentation, I compared soil moisture dynamics at these two sites from July 2022 to February 2024. My analysis centered on a significant precipitation event early in the study period that generated surface runoff and playa inundation, followed by an extended dry period. Although temporal variations in leakage and evapotranspiration are similar at both sites, their rates differ significantly. The UW experienced a higher drying rate, necessitating greater plant water uptake from the subsurface. This led to an increased upward leakage to sustain vegetation, resulting in a leakage value of -205 mm, indicating vertical plant water uptake. Conversely, at the DP, the inundation event was formed by 228 mm of surface runoff, supplementing water inputs from precipitation. This additional water reduced the need for upward soil water movement to sustain plant water uptake, resulting in a leakage value of -97 mm. These findings enhance our understanding of hydrologic fluxes within endorheic basins and improve the applicability of hydrological models and the downscaling of remotely sensed soil moisture products.
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- Award ID(s):
- 2025166
- PAR ID:
- 10556954
- Publisher / Repository:
- ProQuest
- Date Published:
- Format(s):
- Medium: X
- Institution:
- Arizona State University
- Sponsoring Org:
- National Science Foundation
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