SoCal Rain Update: One Step Forward

After 5 long years of drought, a series of powerful storms in January 2017 finally brought heavy rain and snow to California. The short-term impacts of the floods and mudslides have been well covered in the news, but many SoCal residents are wondering if the storms have made a major impact on the drought. Let’s take a look at where we stand in Los Angeles, and at water supplies around the state. As always, remember that in California we measure precipitation from October through the following September; this period is called the water year.

Currently, downtown LA is at 14.33” of rain for the water year. This is just 0.60” short of the yearly average, and already well past any of the drought years. In fact January 2017 alone brought more rain to LA than 3 of the 5 drought years, including last year’s completely ineffectual El Niño.

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The six-year total for 2011-12 through 2016-17 is currently at 53.12”, which is 0.13” less than the record driest six-year period of 1958-59 through 1963-64. Over the last 10 years, we have a rainfall deficit of about 37”. So while this year has been good so far, to start making up lost precipitation from the drought, we still need the storms to keep rolling through over the next few months. Looking a little more broadly at SoCal, we can see that much of the region has fared better than LA.

Looking at major reservoirs in the state, almost all are doing very well. It already seems likely that the state will go into the summer with water storage facilities nearly full, and there’s still a lot of winter to come. Remember this the next time someone tells you there’s no reason to create more storage!

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Taking a closer look at some southern California reservoirs of interest, Lake Cachuma, the largest reservoir for Santa Barbara County, was down to 7% of capacity last fall. This put cities in the area on severe water restrictions and prompted the city of Santa Barbara to reactivate its desalination plant. While this year has certainly replenished Lake Cachuma more than any of the drought years, it doesn’t seem like enough to ease restrictions yet.

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Over in the southern Sierra Nevada, Lake Isabella has finally received some much needed rain as well. This reservoir, on the Kern River above Bakersfield, is the largest in the Tulare Basin other than Pine Flat on the Kings River. Capacity is 568,000 acre-feet, so it’s nowhere near full, though storage is currently kept below maximum due to ongoing seismic improvements to the dam.

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Looking at departure from normal precipitation to date for the water year across SoCal, we can see there’s been some drought relief in the south Sierra, the Coast Ranges, and the SoCal mountains.

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Precipitation indexes for the Sierra Nevada show it’s been a very wet year throughout the range. The north Sierra, corresponding to the Sacramento River drainage, has had 53.2”, already past the water year average of 50.0”, and on record pace (though the breakneck pace of January precipitation would be hard to match).

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The central Sierra, corresponding to the San Joaquin River drainage, is also already past the water year average, with 42.9” to 40.8”. It too is on pace to match some of the wettest years on record.

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The south Sierra, corresponding to the Tulare Basin (Kings, Kaweah, Tule, & Kern Rivers), is just past the water year average, with 30.2” to 29.3”. It’s been a very wet year for the south Sierra, though it might be hard to keep up with 1968-69.

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Looking over to the other side of California, the east Sierra, corresponding to the Owens Valley, snow water content has already passed April 1 averages, with 34.7” to about 24”. This is where the water in the LA Aqueduct comes from, so it’s good news for city water supplies, as we’ll have to buy less water from the State Water Project and Colorado River Aqueduct.

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Peering into the next 7 days, the forecast calls for another round of solid storms for northern and central California.

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Totals for the far south Sierra and SoCal look relatively modest for the next week… let’s hope that, like in January, this powerful NorCal storm is a prelude to strong rainstorms for us!

Editorial: all of the data used for this post came from public sources (National Weather Service, CA Dept of Water Resources, LA Dept of Water & Power). A lot of useful data is created and made available free to the public by government agencies that are going to have their budgets under attack in the coming years. So, you know… call your reps to protest when that happens!

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