If you follow this blog, you know that I have been watching the drought in California rather closely. New data is in, and it doesn’t look good.
Precipitation is seasonal in California. The winter is the wettest part of the year, the summer is bone dry in most locations. California uses reservoirs to collect water during the winter and provide it during the summer. California’s largest “reservoir” is its mountain snowpack. This accumulates during the winter, then melts gradually during the spring and summer. The runoff recharges California’s aquifers, it keeps rivers flowing, and it is collected into man-made reservoirs.
Because it is so important, California measures its mountain snowpack. Because snow can be light and fluffy or heavy and wet, the measurement they use is the water equivalent in inches. Think of it as the depth of water that would result if you melted the snow. A bucket may have 10 inches of snow in it, but if you melt it, the water would only be a 1-4 inches deep.
The water content of the snowpack generally peeks in early April, thus the April measurements are the most important. The California Snowpack Survey for April 1, 2015, found that the snowpack held the equivalent of only 1.4” of water, when the historical average is 28.3”. At one of the measuring sites, for the first time ever, there was no snow at all, the ground was bare (Phillips). (See photos at right.) The bottom line is that California’s most important reservoir is holding about 5% of the water it usually holds.
(Click photos for larger view.)
There are two basic reasons for the lack of snowpack. First, less precipitation is falling. Data from March 2015, has not been posted, but the chart at right shows December – February precipitation in California for the past 10 years. Precipitation has been significantly below average for each of the last 4 years. I suspect that when March data is posted, 2015 will look much worse than it does in this chart.
The second reason is that temperatures have risen. The second chart at right shows the data. Warmer temperatures, especially over the last 2 years, mean that precipitation that would have fallen as snow instead fell as rain. And some of the snow that did fall melted right away.
This is the 4th year of severe drought in California. The state has just put in place the first mandatory water conservation requirements in its history. The following links will take you to a series of articles that the New York Times has been running on the new requirements, and on how the state is coping with the drought.
For the California Snowpack Survey press release: California Department of Water Resources. Sierra Nevada Snowpack Is Virtually Gone; Water Content Now is Only 5 Percent of Historical Average. http://www.water.ca.gov/news/newsreleases/2015/040115snowsurvey.pdf.
The press release contains a link to photos of the Phillips snowpack survey site. If the link doesn’t work, here is the url: https://d3.water.ca.gov/owncloud/public.php?service=files&t=e5a72c13a0d5f1b4f8b49e584a0d8da7.
The precipitation and temperature data for California were obtained using the National Oceanographic and Atmospheric Administration’s Climate At A Glance Data Portal, http://www.ncdc.noaa.gov/cag/time-series/us.