We’re well into Spring now, so let’s look at the water supply picture here in California. Our wet months of December through March are behind us, so we don’t expect much precipitation until next Thanksgiving or so. That means that we will be working off of storage for the next several months. Our storage comes in two forms: water in the reservoirs of the State Water Project and the Central Valley Project and other local projects, plus the frozen reservoir that is the snow pack in the Sierra Nevada. First, the liquid reservoir storage. See:
The overall amount of water in storage is actually quite good, considering how little precipitation the past two years have brought us. But look at the storage in San Luis Reservoir. That is the real problem for us right now. San Luis is a huge reservoir, shared by the SWP and the CVP. Unlike most of the other reservoirs in the system, San Luis gets very little local inflow: essentially all of the water in San Luis is pumped in. And the source of the water for San Luis is the Sacramento River Delta.
The pumps that supply San Luis can fill this enormous reservoir in a few short weeks, if conditions in the Delta allow. However, flow into San Luis is often curtailed or stopped entirely for environmental purposes. That was the case this Winter. When there was enough water available to fill San Luis, environmental restrictions prevented the pumps from operating. And through the Summer and Fall, the flows in the Delta are usually too low to allow for any pumping to fill San Luis.
Unless we get a nice late Spring flow surge into the Delta, we will only have what’s present now in San Luis to supply all the users south of the Delta until next Winter
. And what would bring about such a surge? The second component of our supply, the Sierra snow pack. How does that look as of today? See:
In short, it looks bleak. With the snow pack so low, we are unlikely to get that flow surge into the Delta that we need to replenish San Luis. This is what has led to the California Department of Water Resources doing something unprecedented: they have cut the “Allocation” — the percentage of water that users will receive — for the second year in a row. The allocation stands at 35 percent, and is unlikely to get much higher, despite excellent storage conditions in our largest reservoirs, Oroville and Shasta.
The shortage of water this year will be due almost entirely to environmental restrictions imposed on the pumping operations this Winter. That’s pretty tough to swallow if you are a farmer whose livelihood depends on water.