Climate change insights from long-term soil-moisture data collected across a desert basin

Background/Question/Methods

With global climate change, an increase in the frequency and intensity of extreme climatic events is predicted for many ecosystems—including extreme drought and wet periods.    In arid and semiarid ecosystems, plant community composition and production is primarily limited by soil water availability.  Thus, changes to the timing, duration, and depth of plant available water (PAW) due to extreme climatic events may have profound effects on future ecosystem processes and services in these systems.  Soil properties, landscape topography, and soil-vegetation feedbacks can control the depth, amount, and duration of PAW in the soil profile.  In addition to affecting current dynamics, these relatively static properties will potentially impact plant community resilience to climate change.  Soil water dynamics of deep desert vadose zones are often difficult to model due to extensive soil development and landscape heterogeneity.  Thus, to understand how climate change will affect PAW and soil water balance in many desert systems, analysis of long-term PAW measurements are needed.  To address this need, we analyze a 23-year record of soil water content collected across varying soil types, landscape positions and plant communities on the Jornada Long Term Ecological Research site southern New Mexico USA.  We use the weather variability, as a surrogate for climatic variability, and range of soils, vegetation, and topographic setting represented in the dataset to evaluate how resilience to climatic change varies across the landscape.

Results/Conclusions

The 23 year record presented illustrates the importance of rare weather events and soil-topography-plant community feedbacks for patterns of PAW in this system.  Broad scale deep wetting only occurred during the two extreme, multiyear wet events captured by this study.  Rates and depths of wetting in response to precipitation varied greatly among sites.  During a nearly 10-yr period with low precipitation, long-term whole profile soil drying occurred basin-wide but rates of drying differed among soil types and landscape settings.  Some of the most stable sources of available water in this landscape occurred either deep in the soil profile (> 200 cm), in partially cemented horizons (at ~100 cm), or in run-in locations.  Shallow water sources (< 50 cm) were typically very unpredictable in the summer growing season but were more predictable in the late winter.  We then present a conceptual model, based on spatiotemporal patterns in PAW, of how resilience to climate change will likely differ among soil, vegetation, and landscape settings in arid ecosystems.