Kings River Runoff Could Fall 26 Percent With Global Warming
September 3,2014
Global warming could result in more trees and vegetation at higher elevations of the Kings River watershed helping to reduce annual river runoff in a study that could be generalized to entire Sierra range.
That’s the upshot of scientific modeling being done in the Sierra by scientists from UC Merced and UC Irvine reported in the Proceedings of the National Academy of Sciences this week.
Warming temps could both increase vegetation in the high Sierra and encourage evapotranspiration they say. They conclude this could lead to a 26% decline in river runoff if the average temperature increases 4.1 degrees C by the end of the century. Warming by 1.3 degrees would reduce water flows by 9%.
The Kings River irrigates 1.24 million acres in Fresno,Kings and Tulare Counties also providing water to 14 cities including Fresno and 11 smaller towns
“The Kings River is particularly important for hydroelectric generation and as a source of water for agriculture” the study says. The watershed feeds some 750,00 people.
The runoff from the Kings River fluctuates greatly, ranging from a high of almost 4.5 million acre feet to a low of 390,000 acre‐feet, with an average annual runoff of 1,745,000 acre‐feet. The basin is some1,530 square miles.
In a portend of what could be a new normal – after several dry years Pine Flat Dam on the Kings in early September has about one tenth of its capacity to hold 1 million acre ft of water.
While climate change is known to have the potential to reduce the supply of surface water by accelerating mountain vegetation growth and evapotranspiration (ET), the likelihood and severity of this effect are poorly known says the report.
The scientists led by Michael Goulden and Roger Bales used the upper Kings River basin in California’s Sierra Nevada as a case study of the sensitivity of runoff to increased ET with warming. They found that Kings River flow is highly sensitive to vegetation expansion; warming projected for 2100 could increase ET across the Kings River watershed by 28% and decrease riverflow by 26%.
Moreover, they found a consistent relationship between watershed ET and temperature across the Sierra Nevada; this consistency implies a potential widespread reduction in water supply with warming, with important implications for California’s economy and environment.