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California slips back into drought after unusually dry February

Wednesday, February 26th 2020, 9:29 am - Close to 60 per cent of the state is experiencing abnormally dry conditions and about 10 per cent is experiencing moderate drought.

February in California is usually marked by heavy rain and is often the state’s wettest month of the year, however, many cities have yet to see a single drop of rain.

This winter is showing similar characteristics to winters in previous years that came before intense and persistent droughts. Think back to the 2011-2017 drought -- those years will be remembered as one of the driest on record and was a situation that put a dent in the state’s economy, promoted wildfire activity and brought water rationing to several counties.

GOES17 slider NOAA Aqua Satellite image of California a year apart on February 18th 2019 and February 17th 2020. The image shows a large reduction in snowpack between this and last year. Credit: NOAA

Despite a wetter end to fall, cities like Los Angeles, San Francisco, San Diego and Sacramento have seen very little to no precipitation since the beginning of 2020.

Downtown Los Angeles has only recorded around 8.15 mm of rain between January and the first three weeks of February. The average amount for January and February is around 175 mm and the precipitation season average is already close to 25 mm below normal values. By this time in the season last year, downtown Los Angeles had already recorded 338 mm of rain.

Map 1 20200218 CA text California drought monitor map. Close to 60 per cent of the state is experiencing abnormally dry conditions and about 10 percent moderate drought. Credit: U.S. Drought Monitor

The culprit behind these low precipitation values is a persistent ridge that has stalled over the eastern Pacific Ocean. A ridge is an area of high pressure that is often associated with clear, dry conditions. The presence of this ridge has been steering several rainy systems away from California and up towards the Pacific Northwest and has brought rainy weather to Washington, Oregon, and western Canada.

According to Daniel Swain, a climate scientist at UCLA’s Institute of the Environment and Sustainability, these unusually dry conditions have not happened in 150 years or more and says that “there have even been a couple of wildfires, which are definitely not something you typically hear about in the middle of winter.”

Map 2 Screen Shot 2020-02-24 at 11.29.33 PM Snow pack monitor map. All three sections of the Sierra Nevadas are experiencing below normal snowpack values. Mountain snowpack stores about one third of California’s water supply. Credit: California Cooperative Snow Surveys

The abnormally wet winter and spring in 2019 was followed by near-average precipitation this past fall, both of which kept the drought alarms silent across the state. This January began with an overall snowpack value of 90 per cent of the historical value, but the mild and dry past seven weeks of 2020 have put a big dent in the snowpack, reducing it closer to 50 per cent.

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California mountains were covered in white around this time last year and the snowpack was 125 per cent of average values. All that snow, together with the very active rainfall episodes helped erase any drought scars of the past. Unfortunately, that is not the case this year. California continues to battle with these wet and dry phases that have been amplified in recent times by climate change.

Graph 1 NOAA-Drought area in California Past California drought years. Credit: Drought Monitor NOAA

Warming temperatures will reduce the snowpack, either by a reduction of snowfall accumulation or by an increase in snowmelt. According to Swain, “the future of California in the climate crisis looks warmer and drier not because of the lack of rain, but because of the extra heat drawing moisture out of the ecosystem.”

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