California's Rainy Season Almost Over

The California rainy season is close to its end. Rain-bearing low pressure systems typically stop bringing heavy rains to the state by mid-April, as the jet stream shifts to the north in its usual springtime migration. With no rain in the forecast for the next seven days, and the 16-day GFS forecast showing mostly light rains affecting the northern portion of the state 8 - 16 days from now, California has likely seen at least 90% of the precipitation that it’s going to get this anemic rainy season. That’s a huge concern for a state suffering through its worst winter drought conditions in recorded history, and Sierra snow pack and reservoir levels near record lows. This year’s drought could well be a harbinger of the future, as climate change is expected to cause increased water availability problems in California. The state is going to have to find new sources of water in the future to support its growing population. Where can California find more water?


Figure 1. Predicted precipitation for the 7-day period ending on Tuesday, March 25, 2014. No rain is expected to fall in California in the coming week. Image credit: NOAA/HPC.

Conservation
The most feasible way for California and the thirsty Southwest U.S. to get more water is through conservation. Irrigated agriculture currently consumes more than 70% of the water supply within the Colorado River basin, and is the obvious first place to look to implement water-saving conservation measures. A 2013 publication by the Pacific Institute, "Water to Supply the Land: Irrigated Agriculture in the Colorado River Basin", offers a number of common-sense ways agriculture could use Colorado River water more efficiently. The river's annual flow is about 15 million acre-feet (an acre-foot is the amount of water needed to cover an acre of land to a depth of one foot.) One-third of the Colorado River's annual flow, about 5 million acre-feet, is devoted to irrigating pasture, alfalfa (hay), and other forage crops used to feed cattle and horses. Alfalfa, planted extensively from Wyoming to the delta in Mexico, covers more than a quarter of the total irrigated acreage in the basin. Almost 7% of the river's flow (1 million acre-feet) might be saved by irrigating alfalfa less often (a practice known as “regulated deficit irrigation”). This process reduces crop yields by about 25%, and thus this process costs approximately $81 per acre-foot of water saved. According to Dr. Peter Gleick, President of the Pacific Institute, farmers in Southern California's Imperial Irrigation District are charged as little as $22 per acre-foot of Colorado River water, so some incentives would have to be offered to farmers to get them to implement this water savings plan. (The $22/acre-foot price is an amazingly good deal for a commodity so precious. For comparison, water pumped from rivers in Northern California to Southern California is priced at over $1500 per acre-foot.)


Figure 2. A 2013 publication by the Pacific Institute, "Water to Supply the Land: Irrigated Agriculture in the Colorado River Basin", offers a number of common-sense ways agriculture could use Colorado River water more efficiently.

Shifting to less water-intensive crops can also yield impressive water savings. For example, replacing about 10% of the basin’s irrigated alfalfa acreage with cotton and wheat could save about 1.5% of the river's flow (250,000 acre-feet), at an estimated cost of about $36 per acre-foot of water saved. Other industrial and municipal water conservation efforts could save up to 600,000 acre-feet per year at a cost of about $700/acre-foot before the year 2035, according to the U.S. Bureau of Reclamation.

I’ll discuss four other ways California can get more water in future blogs posts in the coming week.

Jeff Masters