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How Much Rain is Needed to End a Drought? Not Enough For the Southwest U.S.

2 months ago
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The recent record-breaking rainfall in the Southwest United States will not eliminate the region's long-term megadrought status, researchers say. The extra moisture fueled by atmospheric rivers and an El Niño weather pattern has eased parched conditions somewhat.

However, drought persists in areas and the rain has not significantly replenished critical water sources.

Multi-decadal precipitation deficits preceded the current wet period. Returning regional water availability to normal levels would require many more years of ample rainfall.

The rainwater has also done little to bolster supplies for major Southwestern cities. These population centers rely heavily on snowmelt from the Colorado River Basin. That watershed remains drought-stricken.

Recent Years of Heavy Rainfall After Prolonged Dry Period

Before the recent moisture, the Southwest suffered a precipitation shortfall approaching two decades. Matthew Lachniet, a University of Nevada geoscience professor, stated getting back to normal conditions would need further above-average rainfall.

The last truly wet stretch occurred around 1998. Back then, major regional reservoirs neared overflowing after a sopping wet 1980s. Lachniet suggested perhaps another similarly wet decade could restore normalcy.

The broader issue is how the Southwest distributes and sources its water. In Los Angeles, approximately 80 per cent of precipitation exits directly to the ocean without human use.

Large portions of water for Los Angeles, Las Vegas, and Phoenix derive from snowmelt trickling down the still-parched Colorado River Basin. However, much Colorado River water gets diverted to irrigate farmland before reaching cities.


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