Despite the brief “ArcStorm” of early February, streams and lakes throughout Nevada and California are shrinking under returned dry weather. Drought conditions have persisted now since 2000 with two above average precipitation years occurring only in 2005 and 2010. I’m writing this in early March 2015 and the prospect of a large series of storms is not on the horizon.
Meanwhile the US Drought Monitor shows large swaths of California and Nevada in the 2 most severe drought categories. In Nevada, 48% of the state is classified as under a “extreme” or “exceptional” drought – the two most severe categories of drought. One year ago that figure stood at 33%. Even more of California is in those categories at 67% – a slight increase from last year. The Sierra Nevada Mountains, the primary watershed for much of California and western Nevada rivers and lakes, is entirely within the “exceptional” drought classification. Sierra snowpack stands at 20% of normal – the second lowest measurement on March 1 since record keeping began in 1950.
However, the length of the drought certainly is approaching – if not already exceeding – an historic level at 15 years. The cause of the drought is pegged on the persistent high pressure ridge west of the coast of California in the eastern Pacific. The question for scientists and public alike resounds: “Is the drought the result of increasing Carbon Dioxide in the atmosphere and increasing temperatures world-wide?”
A new study published in the Journal of Science Advances by NASA scientists says that a “megadrought” will hit the US southwest and central plains later this century and remain for decades. The Washington Post, reporting on the NASA study, quoted Jason Smerdon that after 2050, there is “overwhelming evidence of a dry shift, way drier than the mega-droughts of the 1100s and 1200s. [The cause] is twofold, reductions in rainfall and snowfall. Not just rainfall but soil moisture … and changes in evaporation that dry out the soil much more than normal.” The article quotes Marcia Kemper McNutt, a geophysicist and editor in chief of the journal Science, “We are facing a water situation that hasn’t been seen in California for 1,200 years.”
Westerners face severe changes in the natural environment as drought continues, since most water resources are already allocated to human uses. Reduced river flows from poor winter snowpack impact Nevadans with dropping levels at Pyramid Lake and Lake Tahoe, dry stretches on the Truckee River as well as the Carson River and Walker River. Wetlands at Stillwater National Wildlife Refuge have already shrunk significantly and negatively affect spring and fall waterfowl and shorebird migration. Pyramid Lake has fallen more than 25 feet in elevation during the 15 year drought. Currently, most of the water in the Truckee River (about 2/3 of the flow) is diverted to farmers in Fallon because the drought has almost dried up the Carson River which under normal snowpack supplies much of the water for farmers.
A Stanford University study just released reports that the most severe droughts in California occur when conditions are both dry and warm and global warming is increasing the probability those two weather events will occur together. As reported in USA Today, the study led by Stanford scientist Noah Diffenbaugh who also said that very dry and warm years together would not occur without humans increasing carbon dioxide in the atmosphere. His study, questioned by some because of its methodology and findings, projected there will be more dry and warm years occurring together in the future.
While it isn’t clear if human-caused climate change is a significant factor in the present drought, it is clear that if it does persist longer, all of the west will face serious consequences. Western fish and wildlife populations could see significant losses as streams, lakes, and wetlands disappear under warm and dry conditions. Likewise, agriculture throughout the west will see declining productivity – even complete loss in some cases. Recreation, a strong and increasingly important economic force in the west, will likely shrink with the dwindling lakes and rivers.
Carbon Dioxide in the atmosphere is now above 400 parts-per-million – the highest level in at least the last 800,000 years according to Scripps Institute of Oceanography. Levels during those previous 800,000 years ranged from under 200 ppm to highs around 300 ppm. Scientists link warming temperatures to rising Carbon Dioxide levels and studies and models show that rising temperatures tend to make wet places wetter and dry places drier.
We could be in for a long dry spell.
[An excellent article online by National Geographic on the California drought and it causes, “Lack of Snow Leaves California’s ‘Water Tower’ Running Low”, is well worth reading.]