Brazil, California Face Specter of Worsening Drought

By Bob Henson
Published: 21:35 GMT le 30 janvier 2015

January has not been kind to two parched corners of the Americas. A large chunk of California’s San Francisco Bay area is wrapping up the month with no measurable rainfall, a first for January since records began--all the way back to 1850 in the case of downtown San Francisco. This week’s U.S. Drought Monitor dataset shows 77.5% of California in the worst two categories of drought (extreme and exceptional), compared to 67.1% at this point last year. There is still hope that February, March, or even April could bring a few wet storms to salvage the rainy season across central and southern California, but for now the atmosphere appears locked in this year’s version of the Ridiculously Resilient Ridge that delivered severe drought and record heat to California in 2014. With virtually no chance of rain through Saturday, the January records below look certain to be broken (or tied, in the case of Redding).

Downtown San Francisco: no rain reported through 1/29 (record 0.06”, 2014)
Downtown Sacramento: 0.01” (record 0.07”, 2007)
Oakland Airport: trace (record 0.04”, 2014)
Monterey: 0.01” (record 0.04”, 2014)
San José: 0.02” (record 0.10”, 1920)
Napa: trace (record 0.11”, 2014)
Redding: 0.26” (record 0.26”, 1984)
Stockton: 0.02 (record 0.14”, 1976)

Figure 1. Frank Gehrke, chief of the California Cooperative Snow Surveys Program for the Department of Water Resources, conducts the second snow survey of the season at Echo Summit, California, on Thursday, January 29. The survey showed the snowpack to to be 7.1 inches deep with a water content of 2.3 inches, which is just 12 percent of normal for the site at this time of year. Image credit: AP Photo/Rich Pedroncelli.

California’s water year--defined as October 1 to September 30--got off to a reasonably promising start. According to NOAA, statewide precipitation was almost two inches above the average of 7.34” for the period October through December, thanks largely to a cluster of very wet storms in December. But those were also very warm storms that added to reservoirs and aquifers in the Central Valley but left the normally snow-clad slopes of the Sierra Nevada shockingly bare. The Sierra snowpack provides about a third of California’s water supply; it’s vital for keeping rivers and streams flowing into the summer, as well as for attracting tourists, skiers, and boarders in winter. On Thursday, the second California snow survey of the winter found 7.1” of snow and 2.3” of liquid in the snowpack at Echo Summit (see Figure 1). The liquid value was only 12 percent of the average for this time of year. As a whole, the northern Sierra snowpack is the lowest on record for January. One of the most stark symbols of the drought is the landscape around Lake Tahoe, where lower-elevation snow has been almost nonexistent. The average snowfall at South Lake Tahoe from October to January is 68.1”. As of January 29, the resort had received just 7.1”, with nothing measurable on the ground since January 2.

Water crisis looms in São Paulo

The state of water supply is far more dire in the region around São Paulo, Brazil, which is the most populous city in the Western Hemisphere and the third largest metropolitan area. The city’s 11 million residents, and the 20 million across the urbanized region, depend on a system of reservoirs that are perilously close to running completely dry in the midst of the region’s worst drought since at least 1930. Almost half of the São Paulo metro area relies on the main reservoir system, Cantareira (see Figure 2), which has slumped to just 5.1% of capacity as of January 29, according to data available online from Sabesp, the local water utility. The crisis is affecting not only water access but power, since the region is highly dependent on hydroelectricity. Sporadic power cuts have been reported, and close to 100 cities have implemented some type of water rationing, affecting some 4 million people. There have also been reports of unofficial rationing in the São Paulo area itself.

Figure 2. View of the bed of Jacarei River Dam, in Piracaia, during a drought affecting São Paulo state, Brazil on November 19, 2014. The dam is part of the São Paulo's Cantareira system of dams, which supplies water to 45% of the metropolitan region of São Paulo and is now at a historic low. Image credit: Nelson Almeida/AFP/Getty Images.

Climatologically, rainfall is ample across this subtropical area, and unlike San Francisco, the São Paulo region hasn’t been completely bone-dry this month. Weather Underground’s monthly summary page for São Paulo's Conghonas International Airport Inter shows that showers and thunderstorms have dropped modest amounts of rain on the city on about half of all days this month, totaling 4.21.” However, this is far short of the average monthly total for January of 13.76" indicated at Conghonas for a period of record extending back at least to 1996. The latest rainfall forecasts for the region are not especially encouraging--the Friday Weather Underground forecast for Sao Paulo predicted near-average rains of about 2" for the coming week, and the Friday morning 12 UTC run of the GFS model predicted near-average rains of about 5" in the Sao Paulo region through mid-February.

Even assuming water can be found elsewhere in the region to help get the city through the immediate crisis, the impacts on power supply may continue to loom large. São Paulo sits more than 40 miles inland and 2600 feet above sea level, making desalination an impractical option. The Center for Climate Change and Security notes the major risks presented by the current drought as well as other droughts that could develop across Brazil in the coming decade and beyond. Although the nation has made great strides in reducing deforestation over the last few years, the losses already incurred cut back on the ability of forests--especially those in the Amazon--to catch moisture and return it to the atmosphere through evapotranspiration. Many studies have shown potential links between the loss of Amazon rainforest and regional droughts, findings that were recently summarized by Antonio Donato Nobre (a senior researcher at the National Institute of Space Research and National Institute of Amazonian Research) in a widely discussed report, “The Future Climate of Amazonia.” No direct links have yet been made between the São Paulo drought and deforestation. However, Nobre cautions: “Because most of the water that irrigates the bread-basket quadrangle of southern South America originates from the Amazon, the future climate of the continent may be considerably dryer. In a worst-case scenario, it would resemble present-day Australia: a vast desert interior fringed on one side by strips of wetter areas near the sea.”

We'll have another post on Monday and will keep an eye on the storm making its way across the Midwest this weekend, which could bring significant snow to New England early next week.

Bob Henson

Figure 3. When water becomes political: Members of the Homeless Workers Movement (MTST) take part in a protest in São Paulo on September 25, 2014, against the rationing of water in neighborhoods on the city’s outskirts. The supply of water to many cities in the state of São Paulo has been hampered by the worst drought since 1930. Image credit: Nelson Almeida/AFP/Getty Images.

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About The Author
Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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