Why Seasonal Prediction of California Winter Precipitation is Challenging

American Meteorological Society (AMS) | December 7th, 2022

Despite an urgent demand for reliable seasonal prediction of precipitation in California (CA) due to the recent recurrent and severe drought conditions, our predictive sk

Despite an urgent demand for reliable seasonal prediction of precipitation in California (CA) due to the recent recurrent and severe drought conditions, our predictive skill for CA winter precipitation remains limited. October hindcasts by the coupled dynamical models typically show a correlation skill of about 0.3 for CA winter (November–March) precipitation. In this study, an attempt is made to understand the underlying processes that limit seasonal prediction skill for CA winter precipitation. It is found that only about 25% of interannual variability of CA winter precipitation can be attributed to influences by El Niño–Southern Oscillation (ENSO). Instead, the year-to-year CA winter precipitation variability is primarily due to circulation anomalies independent from ENSO, featuring a circulation center over the west coast United States as a portion of a short Rossby wave train pattern over the North Pacific. Analyses suggest that dynamical models show nearly no skill in predicting these ENSO-independent circulation anomalies, thus leading to limited predictive skill for CA winter precipitation. Low predictability of these ENSO-independent circulation anomalies is further demonstrated by a large ensemble of atmospheric-only climate model simulations. While low predictability of the ENSO-independent circulation anomalies could be due to chaotic internal atmospheric processes over the mid- to high latitudes, possible underexploited predictability sources for CA precipitation in models are also discussed. This study pinpoints an urgent need for improved understanding of the formation mechanisms of ENSO-independent circulation anomalies over the U.S. West Coast for a breakthrough in seasonal prediction of CA winter precipitation.

Wildfires, Floods, and Climate Variability

University of California, San Diego (UCSD) | May 10th, 2018

The first chapter surveys fire and fuels managers at local, regional, and national levels. Survey results in the form of fire managers’ decision calendars show how clim

The first chapter surveys fire and fuels managers at local, regional, and national levels. Survey results in the form of fire managers’ decision calendars show how climate information needs vary seasonally, over space, and through the organizational network. The study identifies opportunities to use climate information in fire management, including seasonal to inter-annual climate forecasts at all organizational levels, to improve the targeting of fuels treatments and prescribed burns, the positioning and movement of initial attack resources, and staffing and budgeting decisions. The second chapter analyzes National Flood Insurance Program (NFIP) data to quantify the economic impacts of flooding across the western United States from 1978 to 2007. The study compares National Flood Insurance Program data to National Weather Service measures of total damages, and presents a spatial and temporal analysis of daily claims and loss data over this period. The NFIP data reveals that a small number winter-season extreme hydrologic events, covering wide spatial areas, are responsible for a large proportion of total losses. In coastal southern California and across the southwest, El Niño conditions have had a strong effect in producing more frequent and higher magnitudes of insured losses while La Niña conditions significantly reduce both the frequency and magnitude losses. In the Pacific Northwest, the opposite pattern appears, though the effect is somewhat weaker, and less spatially coherent. The third chapter quantifies the economic impacts of flooding due to atmospheric river (AR) events in the western United States from 1978 to 2007, using NFIP claims and loss data. The study confirms that AR-related flood events cause significant economic damages and form the primary source of insurance claims and insured flood losses in the western coastal states. It provides spatial and temporal characterizations of damages as a function of integrated vapor transport (IVT) and antecedent hydrologic conditions. As the magnitude and frequency of wildfire and flood events change in response to anthropogenic climate change, and as economic and demographic contributions to vulnerability increase over time, public policy must adapt to respond. The results in these papers may be used to inform policies to mitigate losses and respond to future disaster scenarios, and may be of interest to policy makers and applied climate researchers alike.

Winnemem Wintu Salmon Restoration Plan for the McCloud River

Winnemem Wintu | February 1st, 2016

The National Marine Fisheries Service 2009 Biological Opinion for salmon specifically calls out for volition passage alternatives to be investigated and considered. [The

The National Marine Fisheries Service 2009 Biological Opinion for salmon specifically calls out for volition passage alternatives to be investigated and considered. [The Winnemem Wintu] have not seen any real evidence that the Pilot Project is even considering this option. Fortunately, the Winnemem Wintu Tribe has a solution to the above, a full repatriation and restoration of the Salmon to the McCloud River, their Spiritual and Cultural home. It is those Spiritual and Cultural ties and beliefs that have sustained us thus far, and will continue to sustain us as we bring our NUR (Salmon) back home. We therefore request that the following Spiritual, Cultural and Practical Fish Restoration Plan be included in the Pilot Project Plan and submitted out for public comment and consideration.

Yolo Bypass Salmonid Habitat Restoration and Fish Passage Implementation Plan

California Department of Water Resources (DWR) | September 21st, 2012

Significant modifications have been made to the historic floodplain of California‘s Central Valley for water supply and flood damage reduction purposes. The resulting l

Significant modifications have been made to the historic floodplain of California‘s Central Valley for water supply and flood damage reduction purposes. The resulting losses of rearing habitat, migration corridors, and food web production for fish have significantly hindered native fish species that rely on floodplain habitat during part or all of their life history. The Yolo Bypass (Bypass), which currently experiences at least some flooding in approximately 80% of years, still retains many characteristics of the historic floodplain habitat that are favorable to various fish species. In approximately 70% of years, Fremont Weir overtops, joining flows from western tributaries. In approximately 10% of years, localized flooding is due to western tributary contributions only (DWR 2008, Woodland gauge, unpublished analysis). The primary function of the Bypass is flood damage reduction, with most of it also managed as agricultural land. The Bypass has also been identified by several State and federal entities as a potential site for habitat restoration to ease pressure on and increase benefits to threatened and endangered fish species. On June 4, 2009, the National Marine Fisheries Service (NMFS) issued its Biological Opinion and Conference Opinion on the Long-term Operation of the Central Valley Project (CVP) and State Water Project (SWP) (NMFS Operation BO). The NMFS Operation BO concluded that, if left unchanged, CVP and SWP operations were likely to jeopardize the continued existence of four federally- listed anadromous fish species: Sacramento River winter-run Chinook salmon, Central Valley spring-run Chinook salmon, California Central Valley steelhead, and Southern Distinct Population Segment (DPS) North American green sturgeon. The NMFS Operation BO sets forth Reasonable and Prudent Alternative (RPA) actions that would allow continuing SWP and CVP operations to remain in compliance with the federal Endangered Species Act (ESA). This Yolo Bypass Salmonid Habitat Restoration and Fish Passage Draft Implementation Plan (Implementation Plan) was prepared jointly by the California Department of Water Resources (DWR) and the U.S. Bureau of Reclamation (Reclamation) to address two specific RPA Actions set forth in the NMFS Operation BO: RPA Action I.6.1: Restoration of Floodplain Rearing Habitat, through the increase of seasonal inundation within the lower Sacramento River basin; and RPA Action I.7: Reduce Migratory Delays and Loss of Salmon, Steelhead, and Sturgeon, through the modification of Fremont Weir and other structures of the Yolo Bypass. As mandated by the NMFS Operation BO, this Implementation Plan describes the activities, process, and timeline required to implement actions to address the requirements of RPA Actions I.6.1 and I.7. Major California restoration planning efforts over several decades (e.g., CALFED, the Bay Delta Conservation Plan) have focused on the Yolo Bypass as a prime area of the Sacramento Valley for enhancement of seasonal floodplain rearing habitat. The Yolo Bypass is generally seen as one of the best places in the lower Sacramento River Basin on which to focus implementation resources in order to achieve implementation of floodplain enhancements because of these efforts. Some of the technical foundation for these efforts has been well laid and interaction with stakeholders and local property owners has been initiated and is on-going. Implementation procedures related to RPA Action I.6.1 within the NMFS Operation BO specify that this Implementation Plan include an evaluation of options to "increase aquatic inundation of publicly and privately owned suitable acreage within the Yolo Bypass." Therefore, this Implementation Plan focuses on restoration of floodplain rearing habitat within the Yolo Bypass to address RPA Action I.6.1. However, the planning and environmental compliance process will consider a reasonable range of alternatives for implementing this RPA action. Additional discussion regarding the availability and suitability of areas for seasonal floodplain inundation is provided in Section 6: Proposals to Refine the RPA Actions.