Pick Our Brain - February 2010

The heavy storms in California recently increased the snowpack and brought it up to normal, so does that mean the drought is over?

The storms that have pummeled California over recent weeks have caused many to ask if the drought of the past three years is over. As discussed in an earlier issue of Science News (April 2009) drought comes in varied forms. Drought can be meteorological, hydrological, agricultural, and socioeconomic. The recent storms have greatly ameliorated the meteorological drought and are making a dent in the hydrological drought. The degree to which the hydrological drought is eased come April will be an important indicator of whether the agricultural and socioeconomic drought is easing or over.

Comparison of California Drought Conditions
  Jan. 27, 2009 Jan. 26, 2010
Extreme Drought 16% 0%
Severe Drought 33% 2%
Moderate Drought 39% 17%
Abnormally Dry 11% 38%
Without Drought 1% 43%

One way to address the effects of the recent storms on the California drought is to compare the conditions one year ago to today. The U.S. Drought Monitor (http://droughtmonitor.unl.edu/) produces weekly drought summaries for the United States. The Jan. 27, 2009 drought monitor had 16 percent of California in extreme drought (particularly in north-central California), 33 percent in severe drought, 39 percent in moderate drought, 11 percent abnormally dry, and 1 percent without drought (the far northwestern part of California). The Jan. 26, 2010 drought monitor, after the series of major storms had hit California, has 0 percent of California in extreme drought, 2 percent in severe drought, 17 percent in moderate drought, 38 percent abnormally dry, and 43 percent without drought. This is a significant improvement from this time last year.

An important measure of the status of the hydrological drought in California will be the snowpack on April 1, 2010. Snowpack estimates near the end of January find the southern Sierra Nevada snowpack at about 126 percent of normal, the northern Sierra Nevada snowpack at 117 percent of normal and the overall statewide snowpack at about 107 percent of normal. This is encouraging, but the April 1, 2010 is the estimate that is particularly important because this estimate provides the best estimate of spring runoff and agricultural water supply. If the next two months bring ample precipitation and a significantly above normal snowpack come April 1, then, we can truly speak of the drought being over.

Drought Conditions in California - January 2009 compared to January 2010