Thursday, January 19, 2017

Rains and Snow Rescue California

After five years, the rains and snow have returned to California. Powerful storms brought flooding in northern California and pounded the San Francisco Bay Area. Blizzard conditions in parts of the Sierra Nevada closed ski slopes, but also brought the snow pack to 161% of normal. By last week less than 60% of California was still in drought and the reservoirs held a combined 18 million acre feet of water. Northern California water managers breathed a big sigh of relief even as flooding inundated northern communities.
from Drought Monitor 2017

Meanwhile, Los Angeles and Orange Counties and much of the Central Valley remained in extreme drought. The new storm front that hit the northwest earlier this week is expected to push into southern California today and relieve much of the drought there. This week’s storms should add another 1-3 feet of snow to the snow pack and more rain is expected next week.

California’s climate is dominated by the Pacific storm track. The mountain ranges cause precipitation to fall mostly on the western slopes. These storms also leave tremendous accumulations of snow in the Sierra Nevada during a wet winter. While the average annual precipitation in California is about 23 inches, the range of annual rainfall varies greatly from more than 140 inches in the northwestern part of the State to less than 4 inches in the southeastern part of the State in an average year. California never seems to have an average year- it’s either drought or flood.

Snowmelt and rain fall in the mountains create the annual flow into creeks, streams, and rivers. California’s surface water infrastructure is designed to capture a portion of these flows to provide water during drought years. What is not captured makes their way into the valleys water percolates into the ground or flows through the delta and to the Pacific Ocean. October 1 to April 15th is the wet season and this year is very wet. 

Once more, California was saved from a water crisis by rationing and by the rains finally coming before they ran out of water. However, the climate scientists say that there is an 80% likelihood that at least one multi-decade drought will hit the southwest between 2050 and 2100. The Central Valley depends on groundwater for irrigation during drought years needs to enhance groundwater recharge during we years. Deliberately recharging groundwater allows aquifers to be managed more like surface reservoirs, and has the potential to increase the state's water storage capacity by millions of acre-feet. During droughts, there's little or no water available for groundwater recharge. But now in a wet years it is time to devote substantial volumes to replenishing aquifers. Research at the University of California found that flood flows diverted onto vineyards infiltrated at an average rate of 2.5 inches per day under sustained flooding. Over irrigation results in water percolating into the groundwater basin. 
from Drought Monitor 2016

In 1995, the Pacific Institute published a report that summarized the condition of the water supply in California stating that “California’s current water use is unsustainable. In many areas, ground water is being used at a rate that exceeds the rate of natural replenishment…” In 2005 the Pacific Institute published another report. Pointing out that water demand and use continued to exceed sustainable supply. California needs to manage their groundwater as a reservoir for drought years.

No comments:

Post a Comment