Subject: The Department of Water Resources and increased drought risk.
DWR held a meeting last week to receive comment on their draft outline of a Climate Adaptation Strategy for water resources.
The draft outline covers floods and sea level rise, but did not mention drought risk anywhere. It's ironic, because the meeting was held in the middle of one of the worst worldwide droughts in over a hundred years, that most scientists link to global warming; see map below.
DWR's 2006 and 2009 Climate Change Impacts Assessments showed no increase in the frequency of droughts in California --- but only because their modelling used the technique of mapping monthly streamflow perturbations onto the historical record -- which implicitly assumes the historical frequency of wet and dry years. DWR's own reports have noted that this is a serious shortcoming.
Contrast this position to studies released by the California Climate Change Center as part of the 2009 and 2012 California Climate Change Assessments that project a huge increase in the frequency and severity of droughts in California, consistent with studies for other regions around the world. The frequency of dry and critically dry years in California is expected to increase by 42% from 2000-2050, and more than double by the second half of the century. There have also been several previous independent studies which showed an large potential increase in drought frequency and severity.
The set of global climate models used in the 2009 and 2012 California Climate Change Assessments also project significant drying in California, especially under the higher greenhouse gas emissions scenario. DWR has criticized this set of models as too dry, pointing to the overall trend of increasing precipitation in the state over the last century, and so has discounted most of the results of studies sponsored by the California Climate Change Center.
However, if you look at regional precipitation, there has been an overall reduction in precipitation in Southern California since 1975. The reduction in Southern California is in agreement with projections by a giant ensemble of models that was used by the Bureau of Reclamation in their 2011 Westwide Climate Risk Assessment. The assessment also predicted significant changes in precipitation in the Southwest, and that that there will be a statewide reduction in precipitation in California by 2070.
All of these new studies and the recent droughts around the world should really be a wakeup call to DWR. Unfortunately, even the modelling for BDCP has questionable assumptions. Looking at the slight statewide increase in precipitation over the last century, the BDCP modelling assumes that wetter and drier futures are equally likely. It partitions the space of all global climate models into wetter and drier models, and weights both equally in projecting reservoir inflows and outflows, and water deliveries. This could greatly overestimate future flows and future deliveries, and greatly underestimate the potential risk from climate change.
I submitted a report (Incorporating Drought Risk From Climate Change Into California Water Planning) to DWR on their outlined climate change adaption strategy that included detailed critiques of their climate change modelling. I believe that it is essential that DWR do a better job of incorporating drought risk into their modelling, and especially for the SWP Delivery Reliability reports that water agencies rely on for planning.
* My response to them was:
I had no idea that DWR was so incompetent. You'll be interested to know that I attended a managers' meeting at MWDSC (18 Aug 2006) at which they got a VERY sharp view of the effects of climate change on CA water from a top guy @ California Climate Change Center. Seems that DWR may be the last organization on earth to realize that stationarity is dead (e.g., see this work on climate change and water rights in California). Too bad they influence water policies and flows!
Bottom Line: DWR can be lazy and/or incompetent if they lack internal incentives or external pressures to manage water for highest and best use, now and in the future.