With almost all of California still in a severe drought or worse, talk between various levels of government and the public is heating up over how to manage the state's precious water resources.  At the Desert Dispatch newspaper in Barstow, a recent story describes how a “[h]ydrologist urges panel to make water decisions now”:

Despite differences in opinion over climate change, one hydrologist believes decisions have to be made now to deal with dwindling water flow in the Mojave River and its affects on groundwater supplies.

'The Mojave River in Barstow, it can be 20 years with no significant flow in that river,' Dr. John A. Izbicki said during a climate change workshop held by the Lahontan Regional Water Quality Control Board recently at the Hampton Inn in Lenwood. Izbicki is a scientist with the United States Geological Survey.

'So the last significant flow occurred in 2010,' Izbicki said. 'I would like to think in 2030 we can be sitting in a room like this talking about the success and merits of what was done today and decided today in light of climate change. Not arguing and discussing about, well, we failed because we didn't correctly anticipate climate change. Knowledge of the past, even if assuming stationary and concluding understanding what this extreme event means in terms of drought. Understanding what extreme event means in terms of water flow and its availability is going to really, really be important in the decision process in understanding climate change.' ...

The existing record (1931 to present) shows large streamflows and subsequent large-scale recharge occurs on average every seven years. But extended periods of up to 20 years can occur without significant flow and recharge of the Mojave River.

Hydrometric data from the USGS itself are available for the Mojave River at Barstow.  Yes, peak flow data go back to 1931, whereas annual flow records appear to start only in 1972.  Here is the flow data since records began in 1931 directly from the USGS.

Some points need to be made.  There are no significant trends in peak flow since records began, nor since 1970, or over the last three decades.  Rather, the correlation over the past 30 years is toward greater flows, not lesser.  Same goes for the annual flow data that starts in 1972.  No significant trends since 1972 or 1984, and over the last 30 years the correlation is toward more flow.  Dwindling water flow?

Another point from the Desert Dispatch story that is confusing is this: “The Mojave River in Barstow, it can be 20 years with no significant flow in that river ... the last significant flow occurred in 2010.”  Now look at the graph above.  If we define 2010-type flows as the criteria for a “significant flow” in the river, it is abundantly clear that the historical record does not show any periods of “20 years with no significant flow in that river.”  The period from 1943 to 1958 is the longest at 15 years, not 20 years, and the next longest low-flow period is 10 years.  I get only 5.9 years on average between significant flows, not seven, with no significant trend towards a lengthening of time between significant flows since records began.  Indeed, the correlation is toward less time between significant flows.

The take-home message appears to be that concerns over low-flow periods and trends for the Mojave River near Barstow may be substantially overstated, and that climate change does not appear to be leading to either lower flows or longer periods of time between significant flows in the river.  Residents of the region need to avoid the shock doctrine and keep these details in mind when making long-lasting water policy decisions.