Somehow, it’s already April, and despite intense media hype and warning, SoCal residents have watched storm after storm deliver rain to northern California but die on the way past Point Conception. The storms that have made it to LA have been mediocre, with limited moisture; the remnants of a tropical storm in September brought more rain than any system since. Through the end of March, this year has been no better for LA than the last four drought years.
If El Niño is going to bring any rain to SoCal, this is the eleventh hour. The April through June period has brought over 5” of rain only 5 times since 1877 (including the 1982-1983 El Niño), and even this amount would leave LA well below normal for the year.
Major water supply reservoirs in northern California have continued to fill up. The biggest reservoirs in the state, Lake Shasta and Lake Oroville, will almost certainly fill to capacity this spring, after starting out the water year about 30% full. Folsom Lake and Bullards Bar will likely fill, and other large reservoirs like Trinity Lake, Don Pedro Lake, and Millerton Lake have risen significantly.
The snowpack in the northern and central part of the state is running close to average, and about 75% of average in the south Sierra, which will keep water flowing into reservoirs through the spring.
The situation in SoCal, though, is dire. While urban areas in LA and San Diego draw water from all across the southwest, the Central Coast is much more dependent on local supplies, with only small State Water Project allocations of NorCal water. Lake Cachuma, in Santa Barbara County, has fallen every year since 2011 and this year was no different. Nearly at capacity in 2011, it currently sits at only 14% full.
Urban water supplies are one thing; we humans will figure out a way to get by. The impact of this fifth dry year on SoCal’s environment is going to be depressing. Wildlife will have tough times finding water. There are going to be a lot of dead trees in the hills and mountains, increasing the fire danger. At this point, all we can do is hope for monsoon moisture and tropical storm remnants to somehow find their way to LA this summer. At least it would do something to help stop forests from drying out.
To see how dry it has been in SoCal the last 5 years, let’s look back to 1877, when weather records started being kept in downtown LA. SoCal is a land of extremes: the wettest water year (2004-2005, 38.25”) had over ten times the rain of the driest water year (2006-2007, 3.73”).
While dry years are common in SoCal, the last 5 years have been severe, and it is unusual to have so many in a row. Water years 2012-2014 were the driest 2-year period in LA’s history, with just 11.97”, 0.69” less than the previous record of 1897-1899. 2011-2014, 2012-2015, and 2013-2016 are the third, fourth, and fifth driest 3-year periods in LA’s history. Water year 2015-2016 doesn’t end until September 31, but we very close to LA’s dry season and 2012-2016 is currently the driest 4-year period by over 2”, with 29.80” – and the current record holder is 2011-2015 with 31.91”, beating the previous record by 1.50”.
As it stands today, the five year period 2011-2016 has had 38.50” of rain, which would shatter the previous record of 45.63” set in 1985-1990. Simply put, since 1877, LA has never had a five-year period where every year was below average by so much.
Even in that context, though, you can see just how variable precipitation is in SoCal. If we look to the driest 6-year periods, 1945-1951 (57.78”) and 1958-1964 (53.25”) are both drier than 2010-2016 (58.70”). Next year would only have to be a normal year to avoid 2011-2017 stealing the crown.
The 1958-1964 period is particularly illuminating. Monthly totals are presented below.
In that 6-year period, LA had 5 years that were every bit as bad as the last 5 years have been – worse, actually – split up by one year of above average precipitation in 1961-1962, with 18.71”. That year would have been below average if not for one monster month, February 1962, which recorded 11.57”, more than any other year in the period and more than the driest 2 years combined.
Furthermore, almost all of the rain that February fell in a 2 week period, with 10.88” between February 7th and 19th. Almost 4” of rain fell on February 8, 1962 alone, and 7.56” fell between February 7th and 11th. That 5-day period saw more rain than the entire water year for 1958-1959, 1960-1961, and 1963-1964.In other words, if not for that one 5-day period in February 1962, the 6-year period 1958-1964 would have been drier than the 5-year period 2011-2016. The last wet year in LA, 2010-2011, was above average thanks to 10.23” of rain in December 2010, of which 7.90” fell in just 5 days.
Precipitation in SoCal is of the ultimate capriciousness, even without humanity running an uncontrolled experiment in geoengineering. Storms struggle to bring rain until conditions are just right, and then the skies open like a breached dam. Hating on California’s water supply system is a popular pastime in much of the country, but it’s exactly the logical thing for a civilization to build in a place like SoCal. LA’s water comes from local supplies, the East Sierra via the LA Aqueduct, northern California via the State Water Project, and Wyoming-Colorado-Utah-New Mexico via the Colorado River Aqueduct. Properly managed, it’s a robust system that ensures reliable supply, and makes much more sense than trying to depend on wildly erratic local precipitation.
(Note: data at left is for LAX, so it doesn’t match monthly totals above. All other data in this post is for downtown LA.)
Looking even longer-term, at decade-long totals, we can see that the last 10 years have been unusually dry, averaging just over 10” of rain a year, the lowest since 1877. However, the 20-year, 30-year, and 50-year trends are unremarkable.
Fortunately, people who know much more about California’s climate have been doing much more detailed research on long-term trends than the armchair analysis above.
Recent research published by Daniel Swain, who writes the excellent California Weather Blog, finds that weather patterns that cause dry years in California are becoming more frequent. However, this does not appear to be at the expense of patterns that cause wet years, which may also be increasing in frequency. The result is that long-term precipitation averages may stay the same, even as global warming causes temperatures to increase, but California’s wet and dry extremes may become even more pronounced.
If long-term trends are leading toward even move variability in California’s water supplies, it heightens the importance of improving water storage and management. If there’s a silver lining to the persistence of SoCal’s drought this year, maybe it will be a continued focus on tackling these challenges.