The Colorado River Basin, a vital source of water for millions of people and ecosystems in the western United States, is in dire straits. A recent study by the University of California, Los Angeles (UCLA) revealed the staggering impacts of climate change on the region. Between 2000 and 2021, the river basin lost more than 40 trillion liters (10 trillion gallons) of water, equivalent to the full capacity of Lake Mead, the largest reservoir on the Colorado River.
The megadrought in southwestern North America that began in 2000 caused the driest multi-decade period in the region in 1,200 years. The prolonged drought has led to significant reductions in river flows and reservoir storage, raising concerns about water shortages in the face of further climate warming.
The Colorado River Basin’s sensitivity to warming is alarming. Lead author Benjamin Bass, a hydrologic modeling specialist at the University of California, expressed surprise at how sensitive the basin is compared to other large basins in the western United States. Critical areas of snowpack in the basin are particularly vulnerable to warming, which led to significant water loss during the recent megadrought.
The study looked not only at the effects of climate change, but also considered the complex response of plants to rising atmospheric carbon dioxide. By analyzing historical warming in snowy and non-snowy areas of the basin, the researchers were able to calculate changes in runoff per degree of warming. This analysis showed that anthropogenic climate change has dried up traditional snowpack and rapidly reduced the runoff that feeds the Colorado River.
To conduct the research, the team used a land surface model to analyze changes in water and land cover. Data sets representing atmospheric conditions, gauges recording runoff, and other hydrologic data were examined. Ground and satellite data were also used to assess changes in vegetation.
The results of the study are alarming. From 1880 to 2021, temperatures in the Colorado River Basin increased by nearly 1.5 degrees Celsius due to climate change, resulting in a 10.3 percent decrease in runoff. However, if the impact of plants is included, the actual water loss is about 13%. This emphasizes the critical role of considering vegetation processes in water resources modeling.
The implications of the results are significant. The loss of such a huge amount of water in the Colorado River Basin has already resulted in reduced supplies and the declaration of the first federal water shortage in 2021. As climate change continues to exacerbate the megadrought, water management and conservation must be prioritized.
Scientists and experts emphasize the urgent need for action. Dr. John Abatzoglou, a climatologist at the University of California, Merced, warns, “This study underscores that climate change is already impacting our water resources and points to the need for urgent mitigation measures.”