Did El Nino Put a Dent in the Major Western Drought?

As the epic El Nino of 2015-2016 continues to fade, this is a good time to analyze what impact it had on the multiyear drought across the western United States.  Many Westerners were excited by the prospect of significant rain and snow that the strong episode of El Nino had been expected to bring during the fall and winter months.  Although it did have a positive impact on parts of the drought-stricken west coast, it could have been more beneficial.

The U.S. Drought Monitor Index Map from last October showed how extensive the drought conditions were in the western United States.  Since the late fall and winter months are when the western United States expects to see additional rainfall and snowfall, that’s a good benchmark to show how extensive the drought conditions were prior to the arrival of the El Nino-influenced rainy season. 

Fast forward to the current Drought Monitor Index map and you can see there was significant improvement in the Pacific Northwest, which experienced a dramatic reduction in the expanse of drought conditions.  While some dry conditions currently exist in parts of Oregon and Montana, the extreme drought conditions are gone.  

There is a simple way to look at the impact the El Nino-influenced winter season of 2015-2016 had in this by comparing the rainfall between this past winter and the previous, non-El Nino winter of 2014-2015.  From November 1, 2014 through May 31, 2015, Seattle, Washington had a rainfall deficit of 2.72”, while from November 1, 2015 through April 30, 2016, Seattle had a rainfall surplus of 11.35”.  That’s a net swing of more than 14 inches of rain in just one year.  Meanwhile, Portland, Oregon, had a rainfall deficit of 5.41” from November 1, 2014 through May 31, 2015, while they had a rainfall surplus of 9.21” from November 1, 2015 through April 30, 2016.  That’s a difference of more than 14.5 inches of rain during the same period.  Such a dramatic difference between a non-El Nino season and a strong-El Nino winter shows what an impact the El Nino event had.

Areas farther south weren’t as lucky though.  While San Francisco had a rainfall surplus of less than one inch from November 1, 2015 through April 30, 2016, the cities of Los Angeles and San Diego have actually seen larger rainfall deficits this winter compared to the 2014-2015 winter season.  That explains why the drought conditions virtually disappeared in the Pacific Northwest while much of California and Nevada remain in extreme to exceptional drought conditions.

The significant El Nino episode this past winter helped enhance the precipitation in parts of the western United States, but it didn’t bring the entire west coast the rainfall it so desperately needs.  The southwestern United States can expect to see some isolated rainfall during the summer monsoon season, but no widespread rainfall is on the horizon.  That’s not good news as the dry summertime heat builds across the desert regions of interior California and the southwestern United States.  Serving to foreshadow the upcoming summer, Phoenix, Arizona saw its first 100-degree temperature of 2016 this past week when it was 102 degrees on May 4.