California drought 2011-2017

from Wikipedia, the free encyclopedia
April 2014: exceptional drought (dark red) in 24% of the national territory
October 2014: exceptional drought (dark red) in 58% of the national territory
July 2016: Exceptional drought now only in Southern California

From the end of 2011 to the beginning of 2017, the US state of California experienced an unusually severe and long phase of drought . Possible connections with global warming are discussed. In the United States, the drought is simply called California Drought .

course

According to the “United States Drought Monitor”, after the last drought-free period in California from June 2011, an “unusual drought” (D0) was initially apparent. Since December 2011 there has been a continuous drought of at least moderate severity (D1), from February 2012 a “severe drought” (D2) began to spread. Since April 2013, almost the entire country has been affected by drought of various degrees of severity; between April 2013 and 2016 it was 100% of the country. "Extreme drought" (D3) has been prevailing in parts of the country since August 2013, and "exceptional drought" since January 2014 (D4, highest score on the scale). In February 2014, the “extraordinary drought” affected approx. 25 percent of California's territory, from July to October 2014 58 percent.

The 2013 calendar year was the driest year in California since records began in 1895. With the exception of February and March, rainfall was also below average from January to October 2014. At the same time, the period from January to October 2014 was the warmest on record (both in California and globally), and 2013 was the fifth warmest year in California (the fourth warmest worldwide).

Compared to the drought in 1977, the amount of precipitation in the winter half-year (November to April) 2013/2014 was greater, but the temperatures were significantly higher (on average around 1.8 ° C). In addition, there were various daily temperature maxima, including an unusual heat wave in January 2014.

The drought continued in winter 2014/2015. January 2015 was the driest on record. The 2015/16 winter rainy season brought normal rainfall. Overall, however , there was less precipitation in the hydrological year up to October 2016 and the snow cover was slightly less than normal. The year was thus also marked by drought overall.

After the greatest amounts of precipitation fell since the beginning of the record in winter 2016/17, there was no area with exceptional drought for the first time in years. In early April 2017, Governor Jerry Brown announced the end of the drought, but at the same time warned of the risk of a new drought.

Expression

The drought phase has been compared in various ways with the most pronounced drought period of 1934, which at that time resulted in devastating dust storms ( Dust Bowl ).

A tree ring analysis revealed that the last comparable drought occurred in California about 1200 years ago. The investigating scientists have shown that, although periods with comparably low levels of precipitation have also occurred in the last few centuries, the combination of low levels of precipitation and long-lasting above-average temperatures combined is responsible for the 1200-year record.

Sierra Nevada

Snow cover of the Sierra Nevada on March 27, 2010 and March 29, 2015

The snow that fell in the Sierra Nevada in winter represents an important reservoir of water for the dry summer months. About 30% of the annual water volume in California comes from this source. High temperatures and lower rainfall during the drought resulted in low snow cover. The snow cover in spring 2014 was the lowest since 1977 and is one of the three lowest since records began. An analysis of the snow cover in the Sierra Nevada over the past 500 years found that 2015 was the lowest since 1500.

causes

In the history of California there has been a recurring drought. Since the 20th century, the duration and intensity of the drought has increased.

Several atmospheric circulation patterns that affect precipitation and temperatures in California have changed significantly. A particularly important mechanism is an unusual high pressure ridge over the American West that prevents depressions (with rainfall) from reaching the mainland. Analyzes of this high pressure ridge in the winter of 2013/2014 showed that it arose in late summer due to the influence of continuous Rossby wave energy in the western North Pacific , which intensified in winter. The high pressure ridge caused wave energy to rise in the direction of the wind, further strengthening the low pressure trough over the northeastern United States, creating a dipole . Instead of reacting to the El Niño-Southern Oscillation (ENSO) and the Pacific Decade Oscillation (PDO) as usual (ENSO was in a nearly neutral state and the PDO was not very pronounced), the dipole and the associated circulation pattern correlated with an ENSO precursor (the "Western North Pacific Pattern"). This connection has become increasingly pronounced since the 1970s, which, according to climate models, is associated with the increased proportion of greenhouse gases in the atmosphere. This indicates that the investigated high pressure ridge in winter 2013/2014 and the associated drought are a possible consequence of anthropogenic global warming . The working group around Noah Diffenbaugh from Stanford University also came to a similar conclusion.

Drought occurs particularly often in California during periods of low precipitation that are also exceptionally warm. The climate in the American Southwest since 1950 has been warmer than any comparable period in 600 years. By increasing warm periods

  • the evaporation increases,
  • more precipitation falls in the form of rain instead of snow,
  • the snow melts earlier and faster,
  • the total water supply stored in the mountains of California in the form of snow is decreasing,
  • the demand for water in agriculture increases.

The probability that dry and particularly warm conditions occur at the same time in California has increased significantly in recent years and will continue to increase due to climate change - according to model calculations, every dry year in a few decades will be particularly warm, with a global warming of 4 ° C and constant precipitation will most likely be affected by large parts of the country by more than 35 years of mega-droughts , with a global warming of 6 ° C this is almost certain for almost the whole country. A first quantification from 2015 estimates the contribution of the increased temperatures due to global warming to the drought from 2012 to 2014 at 8% to 27%.

meaning

Map of water storage and supply systems in California

The water supply in California is of great importance . Economic strength (# 1 in the United States ) and intensive agriculture depend on it. In addition, there has been a population increase of 10 million to 38 million in 25 years. Water consumption has always been a problem in California when winter rainfall was less than expected and the water withdrawal under the natural filling did not balance out. In addition, even in normal years of rainfall, water consumption in California is greater than the natural supply. According to a study, the groundwater level in the Central Valley fell by approx. 20 mm / year between October 2003 and March 2010.

consequences

Satellite measurements by the Scripps Institution of Oceanography as part of the Gravity Recovery And Climate Experiment showed that the desiccation of the land area resulted in a mass loss of the American continental plate and an elevation of the western United States by up to 15 millimeters. The water shortage estimated on the basis of this data was 240 billion tons in March 2014 (compared to the long-term mean). This corresponds to the region being covered with a 10 cm layer of water or the annual loss of mass of the Greenland ice sheet. Satellite measurements since 2002 show that California's water reserves have been declining since at least that time. The groundwater level has been falling since the beginning of the 20th century. About two thirds of the water loss is attributed to the additional construction of agricultural wells as a result of the drought.

The level of California's water reservoirs was 55 percent of the average filling level in November 2014, the lowest since 1977. According to NASA analyzes, the filling level in the water reservoirs of the two longest California rivers Sacramento and San Joaquin was about 42 cubic kilometers below the seasonal one Average. According to calculations, the fill levels of the water reservoirs correspond to the water requirement of one year.

The water shortage has an impact on agriculture in particular. A report from the University of California at Davis found an unprecedented decline in water availability for agriculture in 2014. The economic cost of the drought to California was estimated at $ 2.2 billion. Five percent of the land area could no longer be cultivated. The Central Valley is hardest hit with a crop loss of 810 million US dollars (2.3 percent), losses in the meat and dairy industries of 203 million US dollars and additional costs of 453 million US dollars for irrigation.

The University of California's 2015 report found that the damage caused by the drought that year was significantly higher than in 2014. The estimated total economic cost for 2015 increased approximately 25% to $ 2.74 billion. Job losses among seasonal workers and the area of ​​uncultivated land increased by a further 30% compared to 2014. Nevertheless, agriculture - especially where there were groundwater reserves - was surprisingly resilient. Measured against the overall economic performance of California, the damage is still relatively minor. The rainier winter and spring of 2016 brought the total cost of the drought for 2016 to around 600 million US dollars.

Political measures

Barack Obama , accompanied by Jerry Brown, speaks to farmers in Fresno County

On January 17, 2014, the governor of California declared a drought emergency and urged the population to save water. Many farmers had to reduce their livestock or could not irrigate their fields sufficiently. President Obama visited California with Governor Jerry Brown and Agriculture Secretary Tom Vilsack . Obama promised aid totaling $ 183 million to ensure the farmers' livelihoods. There were also various political initiatives to make more water available to the Central Valley . The New York Times saw in this measure, however, also a political factor in relation to the electoral region contested between Democrats and Republicans.

In view of the persistent drought in the 2014/15 winter season, the governor of California ordered various measures at the beginning of April 2015 to reduce water consumption by 25 percent.

Due to ongoing water scarcity, drastic water use restrictions for California's agriculture were announced on June 12, 2015. Farmers with old water rights were forbidden to take unlimited water from rivers as before. The farmers affected have so far taken twice as much water as the city of Los Angeles uses. Thousands of farmers were affected and some were threatened with economic ruin. The measures aroused sharp criticism from agricultural organizations, which called the regulations "hyperregulatory" and announced legal action against them.

Forecasts

The working group led by Benjamin I. Cook from the NASA Goddard Institute for Space Studies used climate models based on tree ring analyzes to predict that the US Southwest and the Central Plains will have a significantly drier climate in the second half of the 21st century as a result of global warming will come. According to these predictions, the risk of drought in the 21st century will exceed the drought periods of the 20th century and even the driest decades during the Medieval Warm Period .

See also

literature

Web links

Individual evidence

  1. ↑ Christopher Schrader: A crazy high pressure back . In: Süddeutsche Zeitung , April 10, 2015. Accessed April 13, 2015.
  2. ↑ United States Drought Monitor: US Drought Monitor Weekly Comparison ( Memento of the original dated November 30, 2014 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. . Retrieved November 30, 2014. @1@ 2Template: Webachiv / IABot / droughtmonitor.unl.edu
  3. ^ NOAA: Climate at a Glance . Retrieved November 30, 2014.
  4. ↑ NOAA: Average Temperature January - October 2014 . Retrieved November 30, 2014.
  5. ↑ Amir AghaKouchak, Linyin Cheng, Omid Mazdiyasni, Alireza Farahmand: Global warming and changes in risk of concurrent climate extremes: Insights from the 2014 California drought . In: Geophysical Research Letters . tape 41 , no. 24 , December 2014, p. 8847-8852 , doi : 10.1002 / 2014GL062308 ( amir.eng.uci.edu [PDF]).
  6. ↑ a b c Jay Famiglietti: Op-Ed: California has about one year of water stored. Will you ration now? In: LA Times , March 12, 2015. Retrieved April 13, 2015.
  7. ↑ Drought in California: El Niño brings water, but not enough. In: Spiegel Online . March 21, 2016. Retrieved July 23, 2016 .
  8. ↑ a b Natural Resources Agency, California Department of Water Resources (Ed.): Drought and Water Year 2016: Hot and Dry Conditions Continue . ( approx. gov [PDF; 5.2 MB ]).
  9. ^ The Atlantic: A Wet Winter Brings a Green Spring to California , April 12, 2017
  10. ↑ Drought Monitor: California , January 31, 2017
  11. ↑ California declares drought over. In: Spiegel Online. April 8, 2017. Retrieved April 8, 2017 .
  12. ↑ a b Is there a new Dust Bowl looming in California? On: Spektrum.de , October 15, 2014. Retrieved November 30, 2014.
  13. ^ Benjamin I. Cook, Richard Seager, Jason E. Smerdon: The worst North American drought year of the last millennium: 1934 . In: Geophysical Research Letters . tape 41 , no. 20 , October 2014, p. 7298-7305 , doi : 10.1002 / 2014GL061661 .
  14. ↑ Markus Becker: Heat and drought: California experienced the worst drought in the last 1200 years. On: Spiegel Online , December 11, 2014. Retrieved December 18, 2014.
  15. ^ Daniel Griffin, Kevin J. Anchukaitis: How unusual is the 2012–2014 California drought? In: Geophysical Research Letters . tape 41 , no. 24 , December 2014, p. 9017–9023 , doi : 10.1002 / 2014GL062433 .
  16. ↑ California drought: Sierra Nevada snowpack if to 500-year low. In: NOAA News and Updates. NOAA, September 14, 2015, accessed September 16, 2015 .
  17. ↑ a b NASA: NASA Analysis: 11 Trillion Gallons to Replenish California Drought Losses. Press release of December 16, 2014. Accessed February 21, 2015.
  18. ↑ Suzanne Goldberg: California drought: Sierra Nevada snowpack if to 500-year low . In: Guardian . September 14, 2015 ( HTML ). Original work: Soumaya Belmecheri u. a .: Multi-century evaluation of Sierra Nevada snowpack . In: Nature Climate Change . 2015, doi : 10.1038 / nclimate2809 .
  19. ^ Edward R. Cook, Connie A. Woodhouse, C. Mark Eakin, David M. Meko, David W. Stahle: Long-Term Aridity Changes in the Western United States . In: Science . tape 306 , no. 5698 , November 5, 2004, p. 1015-1018 , doi : 10.1126 / science.1102586 .
  20. ^ Daniel L. Swain, Daniel E. Horton, Deepti Singh and Noah S. Diffenbaugh: Trends in atmospheric patterns conducive to seasonal precipitation and temperature extremes in California . In: Science Advances . April 2016, doi : 10.1126 / sciadv.1501344 .
  21. ↑ S.-Y. Wang, Lawrence Hipps, Robert R. Gillies, Jin-Ho Yoon: Probable causes of the abnormal ridge accompanying the 2013–2014 California drought: ENSO precursor and anthropogenic warming footprint . In: Geophysical Research Letters . tape 41 , no. 9 , May 2014, p. 3220-3226 , doi : 10.1002 / 2014GL059748 .
  22. ↑ Daniel L. Swain, Michael Tsiang, Matz Haugen, Deepti Singh, Allison Charland, Bala Rajaratnam, Noah S. Diffenbaugh: The Extraordinary California Drought of 2013/14: Character, Context, and the Role of Climate Change . In: Bulletin of the American Meteorological Society (Special Supplement: Explaining Extreme Events of 2013 from a Climate Perspective) . Vol. 95, No. 9 , September 2014, p. S3-S7 (English, ametsoc.org [PDF]).
  23. ↑ Christopher Schrader : Climate change favored drought in California. On: Süddeutsche.de , September 30, 2014. Accessed December 1, 2014.
  24. ^ Noah S. Diffenbaugh, Daniel L. Swain, Danielle Touma: Anthropogenic warming has increased drought risk in California . In: Proceedings of the National Academy of Sciences . tape 112 , no. March 13 , 2015, doi : 10.1073 / pnas.1422385112 ( HTML ).
  25. ↑ Toby R. Ault et al. a .: Relative impacts of mitigation, temperature, and precipitation on 21st-century megadrought risk in the American Southwest . In: Science Advances . tape 2 , no. October 10 , 2016 ( sciencemag.org ).
  26. ^ AP Williams et al .: Contribution of anthropogenic warming to California drought during 2012–2014 . In: Geophysical Research Letters . 2015, doi : 10.1002 / 2015GL064924 . See also the message Warming climate is deepening California drought. In: ScienceDaily. August 20, 2015, accessed August 21, 2015 .
  27. ↑ Klaus Peter Wittich, Markus Ziese, Andreas Becker: Even at the end of the rainy season: No relaxation for the drought in California. (PDF) German Weather Service , April 17, 2015, p. 2 , accessed on June 6, 2015 (as of April 17, 2015).
  28. ^ Adrian Antal Borsa, Duncan Carr Agnew, Daniel R. Cayan: Ongoing drought-induced uplift in the western United States . In: Science . tape 345 , no. 6204 , September 26, 2014, p. 1587–1590 , doi : 10.1126 / science.1260279 .
  29. ↑ Consequences of the water shortage: Drought makes California grow. In: Der Tagesspiegel . August 24, 2014, accessed December 27, 2014 .
  30. ↑ California Data Exchange Center, Department of Water Resources: Reservoir Water Storage: November (as of December 18, 2014). Retrieved December 27, 2014.
  31. ↑ Drought-stricken California only has one year of water left, Nasa scientist warns. In: The Guardian , March 16, 2015. Retrieved April 5, 2015.
  32. ^ University of California, Davis: Drought impact study: California agriculture faces greatest water loss ever seen . July 15, 2014. Retrieved December 27, 2014.
  33. ^ University of California, Davis: Drought costs California agriculture $ 1.84B and 10,100 jobs in 2015 . August 17, 2015. Retrieved September 5, 2015.
  34. ^ University of California, Davis: Economic Analysis of the 2016 California Drought for Agriculture . August 15, 2016. Retrieved October 29, 2016.
  35. ↑ Dr. Susanne Haeseler: Persistent drought in California in January 2014. (PDF) January 20, 2014, accessed February 7, 2014 .
  36. ↑ Norimitsu Onishi, CORAL DAVENPORT: Obama Announces Aid for Drought-Stricken California. In: New York Times. February 14, 2014, accessed February 23, 2014 .
  37. ↑ Drought: California pledges to conserve water. In: Süddeutsche Zeitung , April 2, 2015. Accessed April 5, 2015.
  38. ^ California orders historic water cuts for farmers. BBC News, June 12, 2015, accessed June 13, 2015 .
  39. ↑ Lisa M. Krieger: California drought: In historic step, 'senior water rights' curtailed. Times Herald News, June 12, 2015, accessed June 13, 2015 .
  40. ^ Benjamin I. Cook, Toby R. Ault, Jason E. Smerdon: Unprecedented 21st century drought risk in the American Southwest and Central Plains . In: Science Advances . tape 1 , no. 1 , February 1, 2015, p. e1400082 , doi : 10.1126 / sciadv.1400082 .