PS 41-130 - Towards Understanding Ecological Drought for Future Climate Projections

Abstract: Drought, heat, fire, invasive species and other stressors that affect dryland ecosystems in the western U.S. and globally are intensifying with climate change. The impact of these changes on water-limited drylands will depend on shifts in ecological drought conditions that represent temporal and soil-depth dynamics of scarce and variable moisture. However, the future of ecological drought is difficult to infer from climate or weather conditions alone because of interactions and feedbacks between weather, vegetation, and soil conditions. Here, we identify the characteristics of drought and water balance approaches that are necessary to appropriately assess future dryland ecological drought in the context of global change. We suggest five critical requirements for developing appropriate assessments of climate change impacts on ecologically-relevant drought in drylands. First, models must employ a reasonably frequent temporal resolution to capture ecologically-relevant drought conditions that can emerge rapidly; fluctuating dry soil events are often not well-represented by meteorological drought indices. Second, models must represent the influence of site-specific soil conditions to appropriately estimate water movement and the availability of that water for utilization by plants. Third, models need to sufficiently resolve the soil profile at multiple depths to represent differential water movement and utilization among plant functional types and across seasons. Seasonal and soil-depth patterns of moisture availability strongly influence the structure and function of dryland plant communities. Fourth, understanding water cycling and drought stress in dryland requires models to incorporate the influence of vegetation, which include vegetation structural impacts on the fate of incoming precipitation and the vegetation physiology that determines patterns and rates of plant water use. Fifth, accurately estimating future ecological drought requires a water balance model that includes the consequences of climate change on vegetation structure and function including responses to increased atmospheric dioxide. We demonstrate one approach to assessing future ecological drought using a mechanistic ecosystem water balance model that includes these five requirements. We illustrate how future changes in drought provide insights into dryland resistance & resilience and inform risk assessments, prioritization of conservation and restoration investments, and climate-adaptive management strategies that can sustain dryland ecosystem services in a changing world.