Increased aeolian activity and dust emission have important ecological and hazard implications. For example, soil loss and redistribution from aeolian activity affects soil health, nutrient cycles and land potential. Dust emissions impact air quality and long-term health and episodic hazards such as dust storms pose immediate threats to human life. As such, understanding potential climate change impacts to wind erosion and dust emission is critical for applying appropriate management and mitigation practices.
Overall, climate change is expected to increase vulnerability to wind erosion in many landscapes of the Southwest (see Edwards et al.9 for detailed review). Projected increases in temperature and carbon dioxide (CO2) concentrations coupled with expected drying and increased precipitation variability are expected to have long-term effects on important limiting controls of erosion, especially vegetation cover and community composition. In addition, the frequency and magnitude of extreme events such as drought, fire and high intensity storms are expected to increase, which could significantly increase vulnerability to wind erosion over multiple scales.
Climate Change Projections
There is very high confidence that CO2 concentrations and temperatures across much of the West have been increasing over the past century, and that this trend is intensifying.10 Predictions from the Coupled Model Intercomparison Project (CMIP5) further suggest mean temperatures across the West could increase by ~3.3°C (6°F) by the mid-21st century and ~5°C (9°F) by late-21st century under the Representative Concentration Pathway 8.5 (RCP8.5), which is consistent with recent observations of emissions. Increases in temperature are projected across all seasons but are higher for summer and fall when many plants are already stressed. Projected warming has the potential to impact wind erosion through further increasing evaporative stress and soil moisture deficits, which in part control vegetation cover and plant community structure.
Observed changes in annual precipitation are more variable, but annual drying trends have been observed for much of the Southwest.11 In general, drying in the Southwest has been observed during spring and summer. Projections for annual precipitation by the mid-21st century under RCP8.5 are more uncertain than for temperature but suggest continued drying,12 with drier winters and springs but wetter summers.
Surface winds in the US have declined by ~10% over the last 30 years.13 Patterns of seasonal wind-speed projections for mid-century are consistent with these evaluations but highly uncertain. Despite the projected decrease in mean winds, most projections include an increase in potentially erosive weather events, such as thunderstorms and severe winter storms. Further, warming and drying conditions favor longer term disturbances which increase vulnerability to wind erosion, such as prolonged soil moisture deficits and large fires.
Potential Impacts on Wind Erosion
Projected changes in atmospheric CO2 concentration, temperature, and precipitation will likely impact vegetation production, cover, and community composition in the Southwest (see Polley et al.14 and Briske et al.15 for detailed reviews). Increased CO2 promotes growth and water use efficiency by plants, but these benefits will likely be limited by water availability. Both Polley et al.14 and Briske et al.15 suggest that coupled warming and drying trends in the Southwest will reduce overall net primary production, reducing vegetation cover, and could favor shifts to more woody species. In addition to an overall drying trend, increased variability in precipitation also decreases overall ecosystem productivity and promotes shrub productivity at the expense of grasses.16 This suggests that prolonged periods of increased variability in precipitation could favor grass-to-shrub transitions, which, once started, are often self-sustaining.
Although lower mean wind speeds are projected across much of the region, any reduction in wind erosion potential could be offset by vegetation responses to climate change. Wind erosion frequency and magnitude depend on the degree of soil exposure to the wind field, which is largely controlled by vegetation cover and community structure. Decreases in overall cover and transitions from high-cover grasses to shrubs with bare interspaces effectively increase long-term vulnerability to wind erosion. In addition, wind erosion and dust emission events are largely driven by frontal passages over much of the region. Dryer winters and springs may further promote increased wind erosion by reducing early season production and thus vulnerability to these events. Local convective winds are also important drivers of dust events in the Southwest. Increased frequency of severe storms would likely increase the frequency of dust-related hazards. Finally, warming and drying could increase the frequency and return interval of wildfires, which would significantly increase wind erosion at local scales during recovery periods.
Given current vulnerability of arid and semi-arid lands to erosion and the uncertainty regarding future trajectories of vegetation cover and community structure, wind erosion should be explicitly considered in management benchmarks and decision support. However, management options to limit wind erosion are largely similar to those already in place to address other disturbances, such as drought, fire, invasive species, and shrub encroachment. As such, implementing active, planned management now that has multiple benefits, including for mitigating erosion, will very likely increase resilience and adaptability in the future.
References
9. Edwards BL, Webb NP, Brown DP, et al. Climate change impacts on wind and water erosion on US rangelands. J Soil Water Conserv. 2019;74(4):405-418. doi:10.2489/jswc.74.4.405
10. Vose RS, Easterling DR, Kunkel KE, LeGrande AN, Wehner MF. Ch. 6: Temperature changes in the United States. In: Wuebbles DJ, Fahey DW, Hibbard KA, Dokken DJ, Stewart BC, Maycock TK, eds. Climate Science Special Report: Fourth National Climate Assessment, Volume I. Vol I. U.S. Global Change Research Program; 2017:185-206. doi:10.7930/J0H993CC
11. Easterling DR, Arnold JR, Knutson T, et al. Ch. 7: Precipitation Change in the United States. In: Wuebbles DJ, Fahey DW, Hibbard KA, Dokken DJ, Stewart BC, Maycock TK, eds. Climate Science Special Report: Fourth National Climate Assessment, Volume I. Vol I. U.S. Global Change Research Program; 2017:207-230. doi:10.7930/J0H993CC
12. Greene AM, Seager R. Categorical representation of North American precipitation projections. Sci Rep. 2016;6:23888. doi:10.1038/srep23888
13. Vautard R, Cattiaux J, Yiou P, Thépaut J-N, Ciais P. Northern Hemisphere atmospheric stilling partly attributed to an increase in surface roughness. Nat Geosci. 2010;3(11):756-761. doi:10.1038/ngeo979
14. Polley HW, Briske DD, Morgan JA, Wolter K, Bailey DW, Brown JR. Climate Change and North American Rangelands: Trends, Projections, and Implications. Rangel Ecol Manag. 2013;66(5):493-511. doi:10.2111/REM-D-12-00068.1
15. Briske DD, Joyce LA, Polley HW, et al. Climate-change adaptation on rangelands: Linking regional exposure with diverse adaptive capacity. Front Ecol Environ. 2015;13(5):249-256. doi:10.1890/140266
16. Gherardi LA, Sala OE. Enhanced precipitation variability decreases grass- and increases shrub-productivity. Proc Natl Acad Sci. 2015;112(41):12735-12740. doi:10.1073/pnas.1506433112