Droughts in California
Drought is generally defined as "a deficiency of precipitation over an extended period of time (usually a season or more), resulting in a water shortage.
"[1] A lack of rainfall (or snowfall) or precipitation in meager quantities, higher than average temperatures and dry air masses in the atmosphere commonly underlie drought conditions; these natural factors are further complicated by increases in populations and water demands.
Since the California water supply is attained from numerous sources, fulfilled by varied and intricate weather patterns, there is no one cause of drought.
[6] Across the Californian region, paleoclimate records dating back more than 1,000 years show more significant dry periods compared to the latest century.
Based on scientific evidence, dry spells as severe as the mega-droughts detected from the distant past are likely to recur, even in absence of anthropogenic climate change.
Although natural variability dominates, anthropogenic warming has substantially increased the overall likelihood of extreme California droughts.
"[10] A study published in 2016 found that the net effect of climate change has made agricultural droughts less likely, with the authors also stating that "Our results indicate that the current severe impacts of drought on California’s agricultural sector, its forests, and other plant ecosystems have not been substantially caused by long-term climate change.
[7] Furthermore, global La Niña meteorological events are generally associated with drier and hotter conditions and further exacerbation of droughts in California and the Southwestern and to some extent Southeastern United States.
Christensen et al. (1980) [25] demonstrated an information-theoretic model predicted the probability that precipitation will be below or above average with modest but statistically significant skill one, two and even three years into the future.
In California, the six-year drought ended in late 1992 as a significant El Niño event in the Pacific Ocean (and the eruption of Mount Pinatubo in June 1991) most likely caused unusual persistent heavy rains.
In the spring of 2015, the National Oceanic and Atmospheric Administration named the probability of the presence of El Niño conditions until the end of 2015 at 80%.
[33] Heavy rains in January 2017 were expected to have a significant benefit to the state's northern water reserves, despite widespread power outages and erosional damage in the wake of the deluge.
[36] Floodwaters caused severe damage to Oroville Dam in early February, prompting the temporary evacuation of nearly 200,000 people north of Sacramento.
[37] In response to the heavy precipitation, which flooded multiple rivers and filled most of the state's major reservoirs, Governor Brown declared an official end to the drought on April 7.
Excessive ground water pumping and aquifer depletion will lead to land sinking and permanent loss of groundwater storage.
Decreasing groundwater levels lead to exposing of underground water storage areas, this will cause lack of soil structure strength and possible sinking if the land above is heavy enough.
Due to the limited capacity of river channels and dam spillways, reservoirs cannot be quickly drained before major storms.
In the coastal and southern parts of the state, and much of the Sacramento River system, the primary threat is rain floods in the November–April wet season.
Shasta Lake, California's largest reservoir, is limited to approximately 71 percent of capacity in the winter in order to control rain flooding.
An example of a reservoir operated for snow floods is Pine Flat Lake near Fresno, which is restricted to about 53 percent capacity well into spring in order to capture summer snowmelt.
[47] However, Pine Flat and other San Joaquin reservoirs are frequently ineffectual in controlling rain floods, because they cannot release water fast enough between winter storms.
Water managers and hydrology experts have criticized the outdated, overly conservative operation criteria at Folsom Dam, citing improved weather forecasting and snowpack measurement technology.
If dry weather is forecast, water is allowed to be stored above the legal flood control limit, rather than being wasted downstream.
[50] In addition, capital improvements such as the $900 million spillway project at Folsom Dam[51] will allow greater flexibility in water releases, making it safer to maintain a high reservoir level during the wet season.
El Niño and La Niña have often been associated with wet and dry cycles in California, respectively (the 1982–83 El Niño event, one of the strongest in history, brought record precipitation to the state), but recent climate data show mixed evidence for such a relationship due in part to the growing impact of human-induced global warming.
The very wet 2010–2011 season occurred during a strong La Niña phase, while the 2014–16 El Niño event, which surpassed 1982–83 in intensity, did not bring an appreciable increase of precipitation to the state.
Meeting EPA water quality standards currently requires allowing billions of gallons per day to flow into the ocean.
[67] Lately, locals have been fighting back against the "stealing" of precious resources by opposing and not allowing huge water draw down facilities to be set up.
