UCR researchers forecast El Nino-type rain for California


California is expected to receive, on average, about 12 percent more rain through the 21st century with more El Nino-like conditions, suggest recent findings by UCR researchers Robert Allen and Rainer Luptowitz.

Allen, assistant professor in the Department of Earth Science, stated in an email that previous climate models and studies “have suggested that California will become drier under future climate change.” However, after analyzing over 38 climate models, Allen observed an “El Nino-like response in the atmosphere caused by the warming of the central-eastern tropical Pacific surface sea temperature.”

Precipitation in Northern California is expected to increase by 14.1 percent. Central California is expected to increase by 15.2 percent. Southern California is expected to decrease by 3.3 percent. They also found that from December through February, when the bulk of precipitation increase occurs for California, precipitation is expected to increase 31.6 percent in northern California, 39.2 percent in central California and 10.6 percent in southern California. Though the increases in precipitation Allen says, “are certainly comparable and probably smaller than to the large interannual variability in precipitation we currently experience,” the important aspect to understand is that our rain seasons will be shorter in duration but of a heavier monsoonal type, similar to El Nino.

Luptowitz, a UCR graduate student who also worked on the project, noted that northern California is expected to receive more rain than SoCal due to California existing within a transition zone. This is why previous “models would sometimes project a dry climate shift or a wet climate shift,” he says, “leading to a lot of uncertainty in this area.”

When asked what methods or models Allen used to ascertain his results, he said, “I used Coupled Model Intercomparison Project version 5, which are the state-of-the-art coupled ocean atmosphere climate models developed by climate organizations in several countries. I also conducted idealized experiments, using Geophysical Fluid Dynamics Lab’s Atmosphere Model version 3 and the National Center for Atmospheric Research’s Community Atmosphere Model version 5, to better understand the cause of increase in California’s precipitation.”

This shift in climatology does not worry Allen nor Luptowitz at all. Rather, Allen states that “It is likely the increase in precipitation will be beneficial and my findings suggest climate change may be less determinantal to California than previously thought.” He does caution, however, that “this is contingent on how the precipitation change occurs, in terms of intensity, frequency and duration.”

Allen also mentioned that one of the global effects of climate change will be increased evaporation. The question to ask, according to Allen, is this: “Is the increase in precipitation larger than the increase in evaporation, leading to an increase in surface water availability?” Precipitation is important for freshwater resources and agriculture but surface water availability (or, the difference between precipitation and evaporation) is more important.

He also emphasized the negative impacts of global warming, which reduces surface snow cover and snowfall, and the associated implications for freshwater resources. Normally, Allen says, “Snow that falls in the winter persists from spring through early summer, when it melts and provides a continued source of fresh water during those seasons, when it tends not to rain in California.” However, the warmer future threatens to melt the snow sooner, reducing the longevity of our freshwater resources and leaving spring and summer dry.

When asked about Allen’s other ongoing or future research plans, he said he plans on looking into “other components of California’s hydrological cycle such as type of precipitation, changes in runoff, soil moisture, evaporation and more. Basically, I will quantify future changes in drought risk for California using these drought metrics.”