Tuesday, January 17, 2017

No Such Thing as a Free Lunch

Monday and Tuesday were rare dry days in California, at least compared to the past month. The recent series of storms with heavy rain and mountain snows wiped out the drought across northern California, but left the southern half of the state relatively untouched. The improvement in the drought situation in the past year is remarkable, though most of this improvement occurred relatively recently. While the storms the occurred the past two weeks were welcome, they also brought too much of a good thing.

The Drought Monitor for California for January 12, 2016 (left), and January 10, 2017 (right).

Even with the drastic improvement in the drought situation, approximately 13 million California residents are still affected by severe to extreme drought. Much of the agricultural Central Valley is still in extreme drought. Over a thousand wells are dry. There may be some improvement in the southern half of the state over the next week as a series of storms slam into the west coast, but drought may not be what residents will have on their mind.

While the rain and snow in the northern half of the state were beneficial in many ways, it also brought its share of misery and damage. The frequent and torrential rains quickly overran the ability of rivers and streams to carry the water within their banks. Flooding and flash flooding was widespread. Runoff rapidly filled reservoirs that were on their last legs to the point that many had to open floodgates to let the excess water out. Heavy rain over southern California the next seven days will likely result some flooding and the threat of landslides. To be sure, central and southern California need the rain, but not all at once. For there to be real relief from the drought impacts the water needs time to seep into the ground to recharge groundwater, a long, slow process. In these heavy rain situations far more water runs off into rivers, stream, and storm drains than soaks into the ground.

Rainfall totals for the past 30 days have been impressive, with totals in the northern half of the state ranging from 12 to 31 inches, with most of that coming in the past two weeks. Snow in the Sierras was equally if not more impressive. The CoCoRaHS observer at CA-PC-1, Soda Springs measured a total of 202 inches of snow since December 18 (that's 16.8 feet)!

Daily snowfall for the CoCoRaHS station CA-PC-1, Soda Springs, CA for the last 30 days.

The snow was so heavy and intense that a number of ski resorts had to close because of road closures and the sheer amount of snow. Heavy, wet snow brought down trees and powerlines.  With many northern reservoirs now full, snow is more important. The Sierra snowpack supplies about one third of California's water supply. It's the snow piling up in the winter and then slowly melting through the spring and summer that keeps water flowing.

Snow water equivalent in the Sierra range is 164 percent of average as of January 13, ranging from 132 percent of average in the Northern Sierra, 162 percent of average in the Central Sierra, and 197 percent of average in the Southern Sierra. An important statistic is the percent of the April 1 snow water equivalent average. The snow that remains as of April 1 is the snow that melts during the warm season to supply water to California. As of January 13 the percent of April 1 average was near to above the record.

The precipitation outlook for the next seven days is both good and ominous for California. A series of storms now strung out over the Pacific will make landfall in the next week, The outlook is good in that much needed rainfall should reach central and southern California this time around. In northern California, more heavy rain over swollen rivers, full reservoirs, and saturated ground will likely cause another difficult period for northern California residents.

Even with the rain so far and more expected, it will not necessarily mean the end of drought worries in California. There is still the rest of the winter and spring to get through, and the challenge will be managing the water that has fallen so far, and that yet to come.

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