Falling water levels in US state more severe than any event since the late 1500s megadrought, say scientists
By Gerard Wynn
California’s ground water levels are dropping and the winter just finished has left snow pack at a fraction of historical levels in a continuing drought, the state’s Department of Water Resources said this week.
California receives about half its precipitation in the months of December, January and February, with much of that falling as snow in the mountains.
The state plans according to “water years” which run from October to September the following year.
“California’s Water Year 2014 (October 1, 2013 through September 30, 2014) has been one of the driest in decades and follows two consecutive dry years throughout the state,” the water department said.
“The drought has no end in sight.” Nearly the entire state is in severe drought, and over two-thirds in extreme drought.
In normal years, the snowpack stores water during the winter months and releases it through melting in the spring and summer to replenish rivers and reservoirs. However, relatively dry weather conditions this year have reduced the amount of snowpack in California’s mountains.
“The water equivalent of the 2014 statewide snowpack began falling in early April after reaching a peak of 10.1 inches and is now below 5 inches, compared to late April’s historic average of about 25 inches,” the water department said.
“Rainfall also has been far below normal during this water year as recorded by weather stations throughout the state. Despite a few storms that brought rain in February and March, electronic readings indicate that precipitation at eight Northern California stations has been only about 60 percent of normal for late April.”
“There’s little expectation of significant rainfall for the foreseeable future.”
All of California’s eight major reservoirs are below historical levels, water department data showed. The largest, Lake Shasta reservoir was at 53 percent capacity compared to an historical average of 62% at the end of April.
The state governor in January declared a state of emergency, asking all Californians to reduce water consumption by 20 percent; directing local water suppliers to immediately implement local water shortage contingency plans; and putting water rights holders across the state on notice that they may be directed to cease or reduce water use.
Earlier this month, the state published a “Drought Operations Plan”, which anticipated exceptional difficulties during the coming summer.
“As California approaches the summer of a third consecutive dry year, economic and environmental challenges for our State are mounting,” the report said.
“Limited water supplies create a crisis that will require extraordinary management measures on the part of water project operators, water quality and environmental regulators, the hundreds of local water agencies that supply most Californians with water, and State residents themselves.”
“In this extraordinarily dry year, all water users, including agricultural, municipal, and fish and wildlife uses will suffer hardship.”
“So far, 2014, has proven abnormally dry and will be classified as critically dry. The months of December and January, typically the wettest of the year, featured a record-breaking lack of precipitation.”
Scientists have used tree ring data to compare water stress over the past decade in the south western United States with the longer historical average dating back to AD 1000.
“The warm-season vapour pressure deficit has been particularly high since 2000 and is the primary driver of an ongoing drought-stress event that is more severe than any event since the late 1500s megadrought,” found authors publishing in the journal Nature Climate Change in 2012.
“The present event has been associated with regional-scale declines in canopy greenness and tree survival, due in part to large bark-beetle outbreaks and increasingly large wildfires. Collectively, the results foreshadow twenty-first-century changes in forest structures and compositions, with transition of forests in the southwestern United States, and perhaps water-limited forests globally, towards distributions unfamiliar to modern civilization.”