A team of researchers used Landsat imagery to analyze changes in vegetation in the Colorado Desert area around Anza-Borrego Desert State Park between 1984 and 2017.
A hot desert climate (BWh) located in Southern California, annual precipitation in the Anza-Borrego Desert area averages 73 mm annually with variability both from year to year and within the season. Rainfall in the adjacent mountain areas like the Santa Rosa Mountains receive substantially more rain, with an annual average precipitation of 770 millimeters. During the summer months, air temperatures regularly exceed 40°C (104°F) in Anza-Borrego.
As part of the Sonoran Desert, plants in arid environments like the Colorado Desert are adapted to conditions of prolonged periods with little or no rainfall and extreme heat, leading some to assume that these biomes would be resilient to climate change. Researchers with the University of California at Irvine used remote sensing to assess long-term trends in vegetation cover using normalized difference vegetation index (NDVI) calculations.
These researchers analyzed an area of 5,000 square miles covering the Anza-Borrego Desert State Park and nearby mountains to understand how the number of plants has varied over the 34-year study period.
What the study found was that deserts environments had a 35 percent loss in vegetation cover, with mountains having a 13 percent decline in vegetation. Researchers found that the decline in vegetation cover was most widespread in the hotter and drier July-September summer period with 87.1% of the study area showing declining vegetation.
According to the researchers, the loss of vegetation cover in deserts is due to significant year-to-year fluctuation in rainfall combined with rising temperatures and wildfires associated with anthropogenic climate change. The study found that areas with a higher decline in rainfall exhibited a greater loss of vegetation cover during the summer months. Areas with a higher increase in temperature also experienced a greater loss of summer vegetation.
While the plants that exist in the Sonoran Desert, such as the creosote bush, yucca, ocotillo, and mesquite, are adapted to extreme environments, researchers contend that the plants already live in an area that is barely habitable so any shift towards an even hotter and drier climate is making the inhospitable for many plants.
Hantson, S., Huxman, T. E., Kimball, S., Randerson, J. T., & Goulden, M. L. (2021). Warming as a driver of vegetation loss in the Sonoran Desert of California. Journal of Geophysical Research: Biogeosciences, e2020JG005942. https://doi.org/10.1029/2020JG005942
Climate change is driving plant die-offs in Southern California, UCI study finds. (2021, June 21). UCI News. https://news.uci.edu/2021/06/21/climate-change-is-driving-plant-die-offs-in-southern-california-uci-study-finds/