California has lost equivalent of a year's rainfall

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  • Author: Statistics Views
  • Date: 06 August 2015
  • Copyright: Image appears courtesy of Getty Images

A new NASA study has concluded California accumulated a debt of about 20 inches of precipitation between 2012 and 2015 -- the average amount expected to fall in the state in a single year. The deficit was driven primarily by a lack of air currents moving inland from the Pacific Ocean that are rich in water vapor.

thumbnail image: California has lost equivalent of a year's rainfall

In an average year, 20 to 50 percent of California's precipitation comes from relatively few, but extreme events called atmospheric rivers that move from over the Pacific Ocean to the California coast. The state as a whole can expect an average of about 20 inches of precipitation each year, with regional differences; but the total amount can vary as much as 30 percent from year to year, according to the study reported in Science Daily.

In non-drought periods, wet years often alternate with dry years to balance out in the short term. However, from 2012 to 2014, California accumulated a deficit of almost 13 inches, and the 2014-2015 wet season increased the debt another seven inches, for a total 20 inches accumulated deficit during the course of three dry years.

The majority of that precipitation loss is attributed to a high-pressure system in the atmosphere over the eastern Pacific Ocean that has interfered with the formation of atmospheric rivers since 2011.

The current drought isn't the first for California, but has been notably severe because, since the late 1980s, California's population, industry and agriculture have experienced tremendous growth, with a correlating growth in their demand for water.

A strong El Niño that lasts through the rainy months, from November to March, is more likely to increase the amount of rain that reaches California, and study lead author Andrey Savtchenko noted the current El Niño is quickly strengthening. "If this El Niño holds through winter, California's chances to recoup some of the precipitation increase. Unfortunately, so do the chances of floods and landslides," Savtchenko said. "Most likely the effects would be felt in late 2015-2016." (Science Daily, July 30th 2015).

References
1. Andrey K. Savtchenko, George Huffman, Bruce Vollmer. Assessment of Precipitation Anomalies in California Using TRMM and MERRA Data. Journal of Geophysical Research: Atmospheres, 2015; DOI: 10.1002/2015JD023573

2. California 'rain debt' equal to average full year of precipitation, Science Daily, July 30th 2015.

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