Is California’s Drought a Harbinger of the Future?

drought mapThree dry years in succession have plunged most of California into exceptional drought conditions that have placed a severe strain on both municipal water supplies and agriculture throughout the state.  Water use is being rationed in many areas, and many reservoir allotments to agriculture have been completely eliminated. Some farm fields have been left idle, causing the layoffs of about 17,000 farm workers, and $1.5 billion in direct costs to agriculture.

$1.5 billion is still a modest fraction of the $45 billion dollar industry, which supplies nearly half of the fruits, vegetables and nuts grown in the United States. Yet drought resilience in California’s agricultural sector has required an ever-greater reliance on pumped groundwater, a resource that is already used in an unsustainable manner. Over-use beyond the ability of replenishment even in wet years has caused water tables in the Central Valley to drop hundreds of feet in the past few decades, and many areas are experiencing substantial land subsidence damaging surface infrastructure.

While other drought-stricken regions of the southwest are experiencing some relief from monsoonal rains, the drought in California continues unabated with no end yet in sight. Earlier this year there was a strong forecast for possible drought relief from the development of an El Nino in the 2014-2015 winter, but that hope has faded considerably. NOAA has downgraded the likelihood of any El Nino from 80% to about 60%, and if one does form, it is unlikely to be a strong one with a reliable promise of rainfall for the West Coast and Southwest.

Toby Ault

Toby Ault

Is climate change playing a role in the current California drought?  As is true for many extreme weather phenomena, periodic droughts have been a part of the California climate for a long time and have played an important role in the state’s history. However, climate change may indeed be a contributing factor making this event more severe than it otherwise would be. The trend for warmer winters has reduced the winter snow pack in the Sierra Mountains, reducing water supplies in spring.  In addition, California set a new high-temperature record during the first half of 2014, beating the previous high of the 120 year period of records by a huge margin. High temperatures greatly exacerbate drought conditions by increasing evaporation from streams, lakes, reservoirs and soils, and increasing plant water requirements.

In the future, climate models indicate that California, like many semi-arid regions around the world, is likely to experience an overall decrease in rainfall if greenhouse gases (GHG) in the atmosphere are allowed to increase and the planet continues to get warmer. A recent study by Cornell researcher Toby Ault and his colleagues integrates information from climate model projections, the instrumental record, and hundreds of years of tree-ring data to estimate future megadrought probability in the Southwest. Their work concludes that, unless GHG emissions are dramatically cut below current levels, the chances of a severe ten-year megadrought in the Southwest this century is 80-90% (California’s current drought is still only 3-years long), a 35 year mega-drought has a 20-50% chance, and a 50 year drought worse than any in the last 2000 years has a 5-10% chance of occurring. If climate change is allowed to proceed unabated, an increased frequency of megadroughts is likely to hit semi-arid regions around the world, destabilizing large human populations by the impacts on water availability and agricultural production.

 



Category: What's With the Weather

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