California Water Science Center

Coping with Drought in the Russian River Watershed

Prepared in cooperation with the California Water Science Center, Sonoma County Water Agency, USGS-National Research Program, and Scripps Institution of Oceanography

By Lorraine E. Flint

Introduction

Figure 1. Map of Russian River study area including basin areas delineated for application of Basin Characterization Model results to SCWA water management modeling.

Figure 1. Map of Russian River study area including basin areas delineated for application of Basin Characterization Model results to SCWA water management modeling.

The National Integrated Drought Information System (NIDIS) has identified the Russian River (RR) as a California Pilot Study Area for drought preparedness. The California Water Science Center (CAWSC) collaborated with NOAA, Scripps Institution of Oceanography, and the Sonoma County Water Agency (SCWA) to prepare a proposal to NOAA for funds to address drought impacts and preparedness in the RR basin. The project was funded by NOAA and salaries for the USGS are to be provided by SCWA. The CAWSC has worked with SCWA for several years to produce a daily model of unimpaired flows for application to their water management model (Russian River Basin Characterization Model; Flint and others, draft).

Problem

Drought in the RR region is keyed to the absence of large winter storms-the RR is winter rain-driven, with a few atmospheric river (AR) storms each year bringing 40-50% of the annual rainfall. Two multi-purpose reservoirs provide storage for warm-season uses, and there is little to no snow pack to extend the runoff season. The same ARs that provide beneficial water supply can also cause flooding when they stall. Thus the reservoirs are operated in the warm season primarily for water supply by the SCWA, but in winter for flood control by the U.S. Corps of Engineers (COE).

This proposed research is motivated and informed by stakeholder needs for climate information to improve drought preparedness. The RR provides water for over 650,000 people in Sonoma, Marin, and Mendocino Counties in addition to supporting Sonoma and Mendocino County wineries, one of the most valuable agricultural areas in the U.S. and a major tourist area. The river also supports 3 salmonid species listed under the federal and state Endangered Species Act (ESA). Consequently, the RR is the focus of a biological opinion (BO) from National Marine Fisheries Service (NMFS) and California Department of Fish and Wildlife (CADFW) aiming to restore species viability while balancing water supply and flood management operations by the SCWA and COE. These often-conflicting mandates are exacerbated by droughts and water shortages. For example, recent experience highlighted the vulnerability of fish to low water flow conditions exacerbated by diversions for protecting vineyards from frost damage during cold snaps.

The combination of flood risk and sustained drought conditions represents a major challenge to water managers, agriculture, endangered species and tourism in the area. Furthermore there is serious concern that climate change will make such extremes more common. In fact, the California State Water Control Board has issued more drought warnings in recent years, indicating a risk-prone system. Anticipating such conditions, new tools and methods will be needed to help cope with them and to enhance ecologic and economic resiliency. This project will bring recent scientific, technical and policy developments to bear on the problem in the context of the RR basin. This basin is a NIDIS pilot activity area, as well as an Integrated Water Resources Science and Services (IWRSS) demonstration area, the NOAA Habitat Blueprint demonstration watershed, and a Hydrometeorology Testbed (HMT) for NOAA.

Objective and Scope

The project engages the lead water management agency in the region, SCWA, the RR NIDIS Pilot Activity group and a team of scientific experts to provide advances in understanding drought that will meet stakeholder needs for drought preparedness and risk reduction. This project will carry out the following tasks:

  1. Evaluate drought-ending AR characteristics using historical observations and new Intergovernmental Panel on Climate Change (IPCC) 5th Assessment Report (AR5) climate projections with tools created for the previous IPCC 4th Assessment Report (AR4) model runs.
  2. Develop a "drought scenario" for the RR by engaging RR stakeholders and by using results from the IPCC model analysis in task 1, as well as lessons learned from the "ARkStorm" scenario for California flooding.
  3. Develop and carry out a process to characterize the drought readiness for the RR in close partnership with SCWA and the RR NIDIS Pilot Activity group, using results from tasks 1 and 2.

Relevance and Benefits

This project will consider several priority water-resource issues identified in USGS Circular 1309 (USGS, 2007), including developing tools with which to predict ecosystem change on the basis of water availability; quantifying, forecasting, and securing freshwater for our future; and, in particular, assessing the consequences of climate change. This proposal will also support capabilities within the CAWSC to develop hydrologic modeling tools relevant to the present science issues underlying the management of watersheds and hydrologic hazards in light of changes expected under future climate conditions. This project relates explicitly to the mission of USGS Water Mission Area to provide scientific information that will be utilized by decision-makers to effectively manage the landscape and water resources for water-related natural hazards, recreational and ecological use, aquatic health, and environmental quality. In addition, the development of these basin-scale modeling tools describing climate scenarios are relevant to other federally managed lands in California for optimization of water resources.

Approach


Task 1. Evaluate drought-ending AR characteristics using historical observations and new AR5 climate projections

CAWSC will collaborate with the USGS National Research Program (NRP) and Scripps to provide the hydrologic simulation of impacts to streamflows and groundwater using characterized ARs as climatic input to the Basin Characterization Model (BCM). Historical climate maps for the RR basin will be analyzed to identify probable AR signatures. Historical climate and climate projections (AR5) will be analyzed to estimate numbers, intensities, structures, and seasonalities of landfalling ARs at the RR basin, including information on gaps between AR storms that likely relate to the development and ending of droughts. The seasonality of ARs is especially important for water management because the rules used to operate reservoirs require releasing "excess" water in the fall and waiting until spring to refill due to flood risks. These model diagnostics for the historical period of record and the projected futures will be validated against observations of AR conditions available from satellite observations for 10 years in this area, data that is unavailable elsewhere. ARs will be diagnosed using methods developed from meteorological and satellite observations and models. The CAWSC will provide simulations of daily unimpaired flows for historical and future conditions characterizing the impacts of ARs. Thresholds to assess probabilities of risk will be defined for drought conditions on the basis of unimpaired flow results and climatic water deficit from the BCM that will be validated with soil moisture observations. These variables are indicative of water supply and landscape stress risks.

Task 2. Develop, apply, and interpret a "drought scenario".

The engagement of RR stakeholders will help to define the climatological and hydrological thresholds that inform management actions corresponding to extreme drought. A climatology representing a plausible, hypothetical extreme drought scenario will be developed for the RR basin in collaboration with Scripps. Methods used in the "ARkStorm" flood scenario, and informed by results from Task 1 climate projection analyses of drought-busting ARs, will be applied to create a scientifically defensible scenario. It will also use analysis of tree ring data reconstructing 423 years of annual precipitation in the region (Griffin et al., 2008), along with the available 100-yr historical precipitation record developed for the BCM and the resulting unimpaired flow record (Flint et al. draft) , for a total of 435 years. The available 100-yr record of climate includes daily maximum and minimum air temperatures that will provide additional information to develop a climatology that is internally consistent among variables, and will inform the calculation of evapotranspiration and heat indices relevant to water demand, landscape stresses, wildfire, and human health. Historical droughts will be identified for the region and these historical precedents will be concatenated in a reasonable sequence to construct a "megadrought." The scenario climatology will be downscaled to the 270-m grid used in the BCM and applied to simulate hydrologic conditions on the landscape and unimpaired flows for application to the RR System water management model run by the SCWA to evaluate water supply implications for the basin.

Implications of landscape stress and increased demand will be evaluated with regard to forest die-off, wildfire, potential invasions of nonnative species, and agricultural losses. Heat indices will be developed to evaluate the stresses to the energy sector and human health. The scenario and resulting impacts will be communicated to stakeholders via NIDIS workshops that will address the design of an integrated drought monitoring and forecasting system for the RR basin, and support the development of an early warning system to provide accurate, timely, and integrated information. Additional research needs will be identified, and a framework for public awareness and education about droughts will be developed.

Task 3. Report study results

CAWSC will collaborate with NOAA, Scripps, and SCWA to develop and implement a process to characterize the drought readiness for the RR and provide reporting and guidance for public dissemination. This process will draw upon the work completed in Tasks 1 and 2 in addition to a NIDIS outreach workshop to develop a report that: (1) summarizes the research completed in the related tasks; (2) develops definitions of drought and water supply deficit; and (3) develops and documents operational and actionable measures that could be pursued by the SCWA and other resources managers to response to potential future droughts. Synthesis of this report will include and leverage related efforts within the watershed, including (a) a water supply reliability analysis of Lake Mendocino to evaluate impacts of potential future changes in land use in the Upper RR basin, (b) activities corresponding to NOAA's Habitat Blueprint studies that are designed to improve water management practices within the watershed, and (c) vulnerability assessments being done to implement climate adaptation strategies for water supply, land use suitability, hazard risks, ecosystems and quality of life via coordination of the Regional Climate Protection Authority (RCPA) with the North Bay Climate Adaptation Initiative (NBCAI). The drought readiness report will be used by these water managers, land use planners, and many other stakeholders within the watershed to inform their respective decisions and actions in utilizing and managing water resources within the watershed.

References

Griffin, D., Woodhouse, C.A., and Stahle, D.W., 2008, Russian River valley precipitation and stream reconstructed from Blue Oak tree rings. Poster developed for the Sonoma County Water Agency.

Flint, L.E., Flint, A.L., Curtis, J.A., and Delaney, C. Reconstruction of historical and future unimpaired flows for the Russian River Basin. Draft journal article.

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