A dry April caused the expected spring-summer runoff into Lake Powell to plunge dramatically, with the water-flow forecast down the Colorado River declining as much in one month as Tucson Water customers use in 10 years.
May’s monthly runoff prediction for the April-through-July period was 65% of average, or 4.6 million acre-feet. That’s 1 million acre-feet less than the April forecast predicted. Tucson Water customers typically use close to 100,000 acre-feet a year. While low runoff this year is highly unlikely to trigger the river’s first major shortage as soon as 2021, it raises the possibility of one in 2022.
A shortage would fall particularly hard on Central Arizona farmers. Flows of water into Powell that would be low enough to cause a shortage in 2022 are likely to occur about 10% of the time, said the U.S. Bureau of Reclamation’s most recent study of its reservoir operations, published in mid-April.