The End of the Current California Drought

 The multiyear meteorological drought over California is rapidly ending.

Considering the enormous precipitation...both rain and snow...during the past month, coupled with the extraordinary precipitation predicted during the next ten days, the precipitation situation over the Golden State has been rapidly and radically altered, with good expectations for a refill of the major reservoirs serving the state.

Let me show you the data....and you can decide.

Some Perspective

As shown in the climatology of annual precipitation shown below, much of California is quite arid, with much of the Central Valley and southeast CA getting less than 10 inches are year (about 1/3 of the state).  Another third of the state (the southern coastal region, portions of the central valley, and northeast CA) get less than roughly 25 inches.   Only a small (about a quarter) portion of the state enjoys more than 40 inches a year,  encompassing the high terrain of the Sierra Nevada and the mountains of NW California).

There is a reason the Spanish did not move into California for a few hundred years--the place was too arid for agriculture.    Today, California supports a huge population and massive agriculture, depending on an extensive reservoir system, the ability to move huge amounts of water southward, and the (irresponsible) tapping of underground aquifers.

California's annual precipitation has always been hit-and-miss, and often unreliable.  The reason is that California is usually south of the main precipitation-bearing jet stream, with a majority of the rainfall coming from periods in which either the jet stream pushes equatorward or a potent atmospheric river pushes into the region (like right now).

A few years of "drought" followed by a few years of heavier precipitation (and often flooding) is the usual situation for California, something illustrated by the informative figure below from UC San Diego/Scripps showing the total water storage (reservoirs plus snowpack) since 1970.   

Not much long-term trend...but multiyear periods of more and less water.  The last few years have been a dry period.

The Big Turn Around

It appears that we are in the midst of a major turnaround in California's water fortunes.

The large-scale weather pattern shifted in December and moisture has been streaming into California, producing huge amounts of rain and snow.    Below are the precipitation totals for the state for the past month produced by the National Weather Service.  Over twenty inches in the higher terrain, with some locations reporting 25-35 inches.  Even lower elevations in the northern part of the state have received 5-10 inches.  San Francisco, for example, received 5.46 inches in 24 h, the second greatest 1-day total in a 170-year record.  Wow.

Considerable flooding has occurred around the State.  

The latest forecasts predict huge amounts in the future.  Below is the latest 10-day precipitation forecast by the European Center model.  Just stunning.  The whole state gets plenty of precipitation, but the stand out is the northern portion of CA, where large areas get more than 15 inches.  Lots of the state gets more than 8 inches.

Forecasts beyond ten days (less reliable, of course) are also wet. Furthermore, La Nina, which tends to make California dry, is now weakening and is predicted to weaken further.

Is the California Drought Ending?

The trouble with predicting the end of the drought is that it can be defined in many ways.  A big issue is the period that one is talking about.

For shorter periods, such as for the water year starting on October 1, the drought is arguably over and will certainly be over in ten days.  Rivers are flooding and the ground is saturated over much of the state (see the current status of the river from the USGS below, blue and black dots are rivers WAY above normal).

The current precipitation departure from normal for the water year (again, since October 1) is above normal for two-thirds of the State, and the predicted precipitation during the next week will extend the normal to above-normal precipitation to the drier northwest side of the State.

 California's current snowpack, critical for maintaining river levels during the spring and summer and for filling reservoirs, is far above normal.  As shown by the latest data, the snowpack is now 142-203% of normal (light blue shows climatological conditions, dark blue line is this year).  Some areas are now at record snowpack levels.

The Reservoirs and the Long Period Drought

The dry conditions of the past few years, coupled with the continued large usage of water, resulted in dropping levels in California's reservoirs.  But this situation is rapidly improving.  Massive rainfall is rapidly raising reservoir levels and a huge snowpack will ensure large additional water.   

Considering the total of current reservoir levels and snowpack, the western Sierra reservoirs should be restored to normal levels (see below). Even without additional heavy rain periods.

The dry northern reservoirs are rapidly increasing, and with heavy precipitation the coming week, should push reservoir levels to near normal by the end of the month.

Consider the huge Lake Oroville Dam in northern CA (below).  Rising rapidly.

Finally, consider the cumulative precipitation at San Francisco for the past two years.

Brown indicates normal accumulation and green was the actual precipitation.  During the past two years, the cumulative actual precipitation fell behind normal, but you can see that we have almost caught up to normal, and I suspect exceed normal within the next 10 days.  Other California observing locations are similar.

Summary

After a dry few years,  a switch to a very wet pattern is rapidly ending the current and cumulative deficiency from normal of California precipitation.  The ground is saturated, rivers are flooding, and there is good reason to expect that the reservoirs will fill to normal levels (some already there).  The "D" word should probably be dropped.

As an aside, one should note that groundwater levels continue to decline, but that is really the result of unsustainable drawdowns of aquifers by agricultural and other interests, not a change in the climate.