![]() The difference is due to above normal temperatures in most of California and high storm snow levels. However, snow water equivalent-the amount of water contained within the snowpack-has lagged overall precipitation. Snow pack in California’s mountains is also well above average and the highest since 2010-2011. In the western US, they contribute as much as 75 percent of surface-water and groundwater supplies. Mountain areas where precipitation collects and drains off, known as catchments, are key sources for river water and water supply. Virtually every corner of the state is above average to date, though anomalies have been much more impressive in the north (see image to the right). If California receives at least average precipitation for the rest of the season, 2016-2017 will become the state’s wettest Water Year on record.but snow pack is lagging behind Precipitation for virtually all of California is running well above average.Ĭalifornia's year-to-date precipitation is nearly the wettest on record (the Water Year runs from October 1 through September 30). On April 1, 2017, the state had received 144.3 percent of its average annual precipitation accumulation, 9 points shy of 1983's record for the date of 153.3. Global warming is increasing the strain on water supplies in California through rising temperature, even in wet years.The decreasing ratio of snow pack to overall precipitation is an indicator of the temperature-driven snow-melt signal in western US snow pack and California. Despite record seasonal precipitation during the winter of 2016-2017, snow pack is lagging behind overall precipitation. ![]() The demand for water storage calls for capturing as much run-off as possible, yet the demand for flood control calls for maintaining reduced reservoir levels behind dams, making it difficult to capture early run-off during the wet season. California dams, many of which are managed to provide both water storage and flood control, are increasingly challenged as the run-off season increasingly overlaps with the wet season.Warming temperatures are shifting snowfall to rainfall and driving a more pronounced and earlier snow melt, increasing the length of the dry low-runoff period and potentially reducing surface soil moisture.California depends upon snow pack for roughly one third of its water supply.October through December 2016 were very wet months in northern California (with precipitation totals about 170 percent of normal by 1 January 2017), but because several of the storms were warm rainfall, snow pack in California by 1 January was only 64 percent of normal.ĭuring March 2017 the average minimum temperature in the Sierra Nevada mountains was 3 to 4☏ above the 1949-2005 average, increasing the forcing of snow melt. 68 percent of California weather stations located between 2,000 and 5,000 feet have experienced declines in the ratio of snow to total winter precipitation from 1949-2004. Warming temperatures convert snowfall to rainfall and enhance snow melt, both of which, in turn, can reduce snow pack.Ĭalifornia's 2016-2017 winter was significantly warmer than average, contributing to the gap between snow pack and overall precipitation, consistent with the long-term trend in California driven by climate change. While winter precipitation came in near record levels, snow pack did not. Overall precipitation in the Northern Sierras came in at 200 percent of average, yet snow pack was only at 148 percent of average on April 1, 2017. One important indicator of California water supply, however, has lagged behind precipitation: snow pack, which supplies 1/3rd of the state's water supply. While no one storm was notably extreme compared to California's historical records, it all added up to one of California's wettest seasons on record. ![]() From November 2016 onward, California experienced several months of unremitting precipitation, including numerous atmospheric rivers and storms that brought heavy precipitation.
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