The West's historic drought in 3 maps
Updated 10:58 AM ET, Thu October 7, 2021
(CNN)More than 92 percent of the West is in drought this week, according to the US Drought Monitor, with six states entirely in drought status: California, Nevada, Oregon, Idaho, Utah, and Montana.
Scientists say the West's historic, multi-year drought is a clear sign of how the climate crisis is affecting not only the weather, but water supply, food production and electricity generation.
Drought conditions have expanded from the West into the the coastal regions of the East this week, particularly from the Mid-Atlantic into Florida. Meanwhile, warmer-than-usual conditions dominated the northern Rocky Mountains and into northern Wyoming, where temperatures were 3 to 6 degrees above normal, this week's Drought Monitor said.
California drought remains significant and there has been little change in the past few weeks, with 100% of the state in drought conditions and nearly half in exceptional drought, the Drought Monitor's most severe category.
The past "water year," referring to the 12 months running from October 1 to September 30, has been one of the driest on record for many parts of California and Nevada, according to the US Drought Monitor. This follows a dry water year in 2020.
In Northern California, for instance, Redding ended the 2020-2021 water year with 14.24 inches of precipitation, breaking the previous record low of 19.38 inches in 1990-1991. In a normal year, Redding would receive around 33 inches of rain.
The drought is also straining water resources. The US Bureau of Reclamation said in September that there's a 3% chance Lake Powell, a major reservoir on the Colorado River, could drop below the minimum level needed to allow the lake's Glen Canyon Dam to generate hydroelectricity next year. In 2023, the chance of a shutdown grows to 34%, according to the bureau's projection.
There is also a 66% chance that Lake Mead could drop below the critical threshold of 1,025 feet above sea level in 2025, the bureau said. If water levels stay below that critical threshold, it would trigger deep water cuts, potentially affecting millions of people in California, Arizona, Nevada and Mexico.
The bureau in August declared a water shortage on the Colorado River for the first time, triggering mandatory water consumption cuts for states in the Southwest beginning in 2022.
As the planet warms, drought and extreme heat will also fuel deadly wildfires. Multiple studies have linked rising carbon dioxide emissions and high temperatures to increased acreage of burning across the West, particularly in California.
The West experienced extremely low rain and snowfall over the past year, compounded by drastically high temperatures. Less rain and increasing heat waves have led directly to drought conditions and water shortages.
The end of the monsoon season, which had brought some short-term relief to the drought in the Southwest US, comes roughly on schedule, but the amount of rainfall across much of Arizona, New Mexico and Colorado was well above average.
The robust rainfall in the Southwest this summer eased drought conditions there, and according to the latest Drought Monitor update, "rains in the Pacific Northwest and into the Four Corners regions were the only areas with above-normal precipitation for the week."
As climate change accelerates and winter temperatures increase, snowfall will decrease. High-elevation snowpack serves as a natural reservoir that eases drought, storing water through the winter months and slowly releasing it through the spring melting season.
Stream and river flow
Streamflow, a measure of how much water is carried by rivers and streams, is another significant indicator of drought and its impact.
As drought conditions have worsened in 2021, hundreds of stream and river locations are experiencing below-average flow. Fishing restrictions have also been put in place on many rivers in Montana due to low flows and warm waters.
Changes in streamflow affect the water supply for municipal use such as drinking and bathing, crop irrigation and power generation.