Climate Change Drains Reservoirs in the U.S. 

Shasta Lake, a reservoir in northern California, is pictured from the International Space Station as it orbited above the western United States. Photograph by Chris Cassidy, JSC

Zara Gounden, Circle of Blue – July 23 

Reservoirs across the United States and globally are reporting significantly higher evaporation rates.Within the first three weeks of July’s record-breaking temperatures, for example, California’s largest reservoir, Shasta Lake, lost an estimated 4.1 billion gallons of water, due to evaporation.

During July, with temperatures consistently exceeding 100 degrees, Trinity Lake and New Melones Lake in California also experienced significant water losses. Millions of gallons  evaporated from these lakes, far surpassing the  water-loss rates recorded over the past five years.

Climate change has led to an increase in higher temperatures leading to more evaporation. Warmer air holds more moisture, increasing the rate at which water is converted from liquid to vapor. Reduced rainfall and higher temperatures cause more water to be drawn from reservoirs to meet increased agricultural and urban demand, exacerbating water loss.

A study in 2022 found that over the past 33 years, evaporative water loss from reservoirs has been increasing annually by 5.4%, exceeding the global trend of 2.1% for all lakes.

In order to combat water evaporation, methods have included the use of shade structures, floating covers, chemical treatments, and vegetation around water bodies to provide shade and reduce wind speed. However, these methods need to be implemented in conjunction with efforts to reduce the effects of climate change, as rising temperatures and changing weather patterns continue to exacerbate water loss.