Ecohydrology and Climate Change in Drylands

Science Center Objects

Drylands cover 40% of the global terrestrial surface and provide important ecosystem services. However, climate forecasts in most dryland regions, especially the southwest U.S., call for increasing aridity. Specifically, changing climate will alter soil water availability, which exerts dominant control over ecosystem structure and function in water-limited, dryland ecosystems.  This research seeks to understand the spatial and temporal patterns of these changes and assess their consequences for drylands

Background & Importance

Climate forecasts in dryland regions around the world call for increasing aridity and associated drought stress to vegetation. As a consequence, assessing the future of water cycling and availability for dryland vegetation has been identified as an important knowledge gap by land management agencies.  Understanding these impacts requires accurately representing soil water availability, which exerts dominant control over ecosystem structure and function in water-limited, arid to semiarid ecosystems.  Specifically, resource managers need insight into the current and future soil water availability patterns over time, across space and through the soil profile.  However, representing soil water availability complex, because soil moisture responds to the dynamic combination of weather (including previous time periods) and soil conditions (particularly soil texture and depth.  Furthermore, resource managers need insights about soil moisture over broad areas that encompass substantial variability in climatic, topographic and edaphic conditions.

Semi-arid shrubland in foreground with hills and snow-capped mountains in background

Drylands are highly heterogeneous ecosystems, as this image of an elevational gradient in southern Utah illustrates. (Credit: John Bradford, USGS. Public domain.)

General Methods

SBSC researchers are developing and applying appropriate ecohydrological models of ecosystem water balance and plant water availability. To characterize soil moisture dynamics, they designed and coded process-based mechanistic models of water movement through the vegetation canopy, the litter and the soil profile. These models are used to understand climate change impacts on ecological drought at scales relevant to land management, which requires running these models at daily time scales for multiple decades into the past and future across thousands of spatial locations for dozens of climate model forecasts.  SBSC researchers synthesize the resulting datasets into publications and approachable spatial datasets. These models are tools for translating information about weather and soil conditions into more biologically-relevant metrics of soil moisture.  The results quantify the spatial and temporal patterns of ecological drought and assess the potential consequences of climate change for vegetation dynamics in drylands across the globe.  This work has been supported by funding from the Southern Rockies LCC, Desert LCC, the National Park Service and the Powell Center for Environmental Synthesis and Analysis.

Important Results

Ecohydrological modeling translates climate and soil conditions into quantitative measures of drought stress for drylands

Our research has illustrated that availability of water in the soil exerts dominant control over vegetation dynamics and species composition in arid and semi-arid ecosystems.  Such moisture availability metrics are better predictors of ecosystem dynamics than temperature and precipitation alone and can thus provide more nuanced and appropriate insights about the potential consequences of changing climate.

Future droughts will be change where and when water is available for plants

We found that over the 21st century, temperate drylands may contract by a third, primarily converting to subtropical drylands, and that deep soil layers will be increasingly dry during the growing season. These changes imply major shifts in vegetation and ecosystem service delivery.

Soil moisture conditions will dictate shifts in global patterns of rainfed agriculture

We discovered that suitability to support rainfed agriculture is driven by the interactions of warm wet soil, and extreme high temperatures.  21st century ecohydrological forecasts imply shifts and overall increases in the area suitable for rainfed agriculture in temperate regions, especially at high latitudes, and pronounced, albeit less widespread, declines in suitable areas in low latitude drylands, especially in Europe. 

USGS researchers near a rainfall manipulation plot in an arid landscape in northern Arizona.

SBSC researchers use experiments of rainfall to understand how ecosystems respond to drought.  This site in northern Arizona is part of an experiment arrayed across an elevational gradient that will provide insight into the likely impact of climate change on plant communities and ecosystems in dryland regions. (Credit: John Bradford, USGS. Public domain.)

Future Directions

Incorporating soil moisture into vegetation monitoring in drylands

In cooperation with the National Park service and other DOI agencies, this project integrates measures of soil water availability and ecosystem water balance into monitoring efforts.  Results will provide insight into how the response of vegetation to climate changes will vary across lands managed by DOI.  

Assessing climate change impacts along environmental gradients in the southwest

This project will leverage a $4 million investment by NSF and University partners to examine how altered precipitation patterns will impact vegetation across a temperature gradient in Northern Arizona. 

Albedo modification impact on western US dryland ecosystem water balance

In a recent editorial in the journal Science, Marcia McNutt, former USGS Director and chair of a National Research Council report on albedo management, identified several important knowledge gaps associated with albedo modification to mitigate global warming. The editorial, “Ignorance is not an option”, is a strong appeal to the scientific community to begin investigating the potential consequences of global albedo modification. This work will investigate the ecosystem-scale ecohydrological consequences of global albedo modification on western US dryland ecosystems. 

Identifying ecohydrological controls over restoration success

Resource managers need help determining when soil water conditions are likely to support successful plant restoration or regeneration. We seek to address that need by quantifying how soil water controls determine regeneration success for key, widely utilized restoration species, and integrating this knowledge with existing drought forecast products to create a tool for land managers to optimize seeding success.  Results from this work will inform decision support tools to help resource managers insure that seeds are deployed at times when they can effectively compete with exotics. 

Decision support tools to maximize restoration success

We propose to develop a web-based application that integrates emerging seasonal and multi-year weather forecasts to generate customized, site-specific information about climate impacts on natural resources.  This application will allow resource managers to easily obtain historical information as well as both short-term and long-term eco-climatological forecasts about their particular site.  This decision support tool has the potential to enhance the effectiveness of resource management decisions and maximize the efficiency of the millions of dollars spent annually in the U.S. on restoration activities.