Christopher C. Burt is the author of 'Extreme Weather; A Guide and Record Book'. He studied meteorology at the Univ. of Wisconsin-Madison.
By: Christopher C. Burt , 8:09 AM GMT on February 25, 2017
It’s amazing what a difference one year can make. California’s five-year long drought has come to a dramatic halt (or at least interruption) this winter season. The latest California Drought Monitor report, released on February 23rd, has no portion of the state under ‘Extreme Drought’ conditions for the first time in four years. Last year on this date 61% of state was enduring such. Here are some details about the rain and snowfall so far this season.
No pair of graphics can illustrate so clearly how the California drought has virtually come to end as these state drought monitor maps for Feb. 23, 2016 and Feb. 23, 2017 below:
The rainy season (July 1-June 30) for California has already exceeded the normal seasonal totals as of February 23rd with at least two normally wet months still to come. Below is a table listing a select group of California sites and where they stand precipitation-wise as of the end of the latest big storm on February 20th:
Note that most sites in California have already surpassed their average precipitation totals expected for an entire season. The above table and data courtesy of Jan Null, Golden Gate Weather Services.
Santa Rosa has already almost achieved its wettest season on record with a 51.60” sum (actually now up to 51.85” with post storm showers on Feb. 21-22). Their wettest season on record (with a POR beginning in 1902) was that of 1982-1983 with a 55.66” seasonal precipitation total. The additional 3.81” needed prior to July 1st to break the record is a virtual certainty (normal rainfall for March-June is 8.31”). Blue Canyon, at a 5,000’ elevation in the northern Sierra, also has a shot at their wettest season on record with 94.90” observed so far (an additional .37” accumulated in the days following the table’s creation). The site’s wettest season on record was that of 1994-1995 when 122.35” was measured. Normal March-June precipitation for Blue Canyon is 19.07”. Several rain gauges in the northern Sierra have already measured over 100” of precipitation this season, with Four Trees in Plumas National Forest in the Feather River Watershed now up to 124.85”. This site is located in the mountains above the nearly stricken Lake Oroville Reservoir. Closer to the San Francisco Bay Area, the perennial wet spot, Venado in Sonoma County north of the city, has picked up 120” of rainfall so far this season. The California state record for seasonal rainfall is more than likely safe: 257.90” at Camp Six in Del Norte County (in extreme northwestern California) during the 1981-1982 season. The state record for one month of precipitation also was measured at Camp Six with 81.90” in December 1981.
Many of the state’s reservoirs are now at or close to full capacity for the first time in five years. As you may have heard, Lake Oroville faced a crisis last week when the lake overflowed and one of the reservoir’s emergency spillways almost collapsed. Since then the water district authorities have released a huge amount of water from the dam lowering its current level down to just 80% of capacity (see map below). The state’s largest reservoir, Lake Shasta, is now at 93% capacity. Last year at this time it was at 83% and at one point, during the peak of the drought in 2015 it was as low as 37% of capacity.
Much of Blue Canyon’s precipitation has fallen as snow although most of the wettest storms so far this season have been warm atmospheric-river events with high altitude snowlines (generally above 7000’). At the highest altitudes truly phenomenal snowfalls have occurred, although we must rely on the ski resorts for most of the figures at this point. At the top of the list for seasonal accumulation is Sugar Bowl Ski Resort, near Donner Summit, which has reported 585” of snowfall so far at its base. Nearby Boreal Ski Resort has reported 557” and Mammoth Ski Resort 515”. The greatest snow depth so far reported is an amazing 350” (almost 30 feet!) at the 11,000’-level of Mammoth Mountain in the central Sierra. Note that the California state record for seasonal snowfall is 884” at Tamarack (near where Kirkwood Ski Resort is today) and the greatest snow depth ever measured was 451” (37.6’), also at Tamarack, in March 1911.
Snow depths and conditions for some of the Sierra’s ski resorts as of February 23rd.
Overall, the snow-water content in the Sierra is on track to be the greatest such on record in the central and southern Sierra districts, and close to such in the northern district. The season to match or beat was that of 1982-1983 that saw a very wet March, so the same would have to occur this March for any records to be set. At this time, February 24th, the forecast is for a long spell of dry weather for most of California until at least March 10th. Of course, this forecast could change at any time.
California snow-water content as a percentage of normal for this season (as of Feb. 23rd) compared to normal (the blue area) and the wettest, driest, and last season. Note how the driest season on record for all three Sierra districts was that of 2014-2015, just two years ago! Graphs courtesy of the California Department of Water Resources.
Is the Precipitation Regime becoming more Extreme in California?
As the graphs above illustrate, the Sierra went from one of its driest (if not driest) precipitation seasons on record (that of 2014-2015) to possibly one of its wettest this season of 2016-2017. Although this might seem extreme, the record shows that these feast and famine episodes are a fairly common trait of the climate of California. See below:
Chart of annual precipitation season (July-June) totals for the entire state of California 1895-2016. From NOAA’s NCEI Climate at a Glance archive.
Precedent for the wild swing from drought to flood (and visa versa) has been seen in the past: out of 121 seasons 1976-1977 was ranked the 2nd driest whereas 1977-1978 was ranked as the 4th wettest statewide. 1993-1994 was the 8th driest, 1994-1995 was the 3rd wettest, etc. Curiously, if one displays a trend line for the entire POR (1895-2016) there is virtually no change (well, virtually none: drier by .03” per decade statewide). Of course, California is a huge state ranging north to south some 800 miles, but the difference in the seasonal precipitation is only minor from north to south. In the southern drainage district the change is more pronounced: .12” drier per decade and for the northern district just .01” drier per decade, but for the central district .02” wetter per decade. So statistically for the state overall, it is not getting much drier or wetter over the past 121 seasons. Even if this season (2016-2017) ends up as one of the top 10 wettest on record this would not be at variance in terms of extreme variability from episodes in the past that went from extremely dry to extremely wet and visa versa.
So is this season a drought-buster? In most ways, yes. However, whether the crucial aquifers are replenished remains to be seen. California’s ‘water problems’ are likely going to be a permanent feature of life as the state’s population continues to grow out pacing the means to provide it with reliable water sources.
Christopher C. Burt
The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.