Levee Decisions and Sustainability for the Sacramento-San Joaquin Delta

University of California, Davis (UC Davis) | August 15th, 2010

Leveraging Wetlands for a Better Climate Future

San Francisco Estuary Institute (SFEI) | July 15th, 2022

Managing Natural and Working Lands (NWL) to enhance carbon sinks and limit greenhouse gas (GHG) emissions is a key component of California’s ambitious strategy to achie

Managing Natural and Working Lands (NWL) to enhance carbon sinks and limit greenhouse gas (GHG) emissions is a key component of California’s ambitious strategy to achieve net carbon neutrality by 2045. The California Air Resources Board (CARB) Climate Change Scoping Plan includes 7 NWL categories in its GHG emission reduction scenarios, one of which is wetlands. Coastal wetlands in California are a high- leverage NWL type for GHG management relative to their small spatial footprint. These ecosystems have high rates of carbon sequestration and can accumulate large stocks of carbon, due to high productivity, efficient sediment trapping, and low decomposition rates (Chmura et al. 2003, Mcleod et al. 2011). In the absence of management interventions focused on wetland conservation, however, conversion of coastal wetlands to other land uses such as agriculture, grazing, development, impounded wetlands, or subtidal or upland habitat can halt or reverse carbon sequestration, and can shift these ecosystems from long-term GHG sinks to large GHG sources (Hatala et al. 2012, Tan et al. 2019). Filling of wetlands for infrastructure and development was a common practice throughout the early 20th century (Goals Project 1999), dramatically reducing the state’s coastal wetland area and associated carbon sink.

Limiting fossil fuel production as the next big step in climate policy

Nature Portfolio (Springer Nature) | November 26th, 2018

Despite the current ambivalence of the United States towards the Paris Agreement, national and local jurisdictions across the globe remain committed, and they are seeking

Despite the current ambivalence of the United States towards the Paris Agreement, national and local jurisdictions across the globe remain committed, and they are seeking ways to increase the ambition and effectiveness of their climate policies. One way forwards could be limiting the production — not just the consumption — of coal, gas and oil. Here we describe the rationale for, and CO2 emissions implications of, limiting oil production. Seven countries have recently imposed such limits, and we develop a case study for a potential addition to this group, the US state of California. We find that by ceasing the issuance of permits for new oil wells, California could reduce global CO2 emissions substantially and also enhance environmental justice in the state.

Linked fire activity and climate whiplash in California during the early Holocene

Nature Portfolio (Springer Nature) | November 23rd, 2022

Recent wildfire activity in semi-arid regions like western North America exceeds the range of historical records. High-resolution paleoclimate archives such as stalagmi

Recent wildfire activity in semi-arid regions like western North America exceeds the range of historical records. High-resolution paleoclimate archives such as stalagmites could illuminate the link between hydroclimate, vegetation change, and fire activity in pre-anthropogenic climate states beyond the timescale of existing tree-ring records. Here we present an analysis of levoglucosan, a combustion-sensitive anhydrosugar, and lignin oxidation products (LOPs) in a stalagmite, reconstructing fire activity and vegetation composition in the California Coast Range across the 8.2 kyr event. Elevated levoglucosan concentrations suggest increased fire activity while altered LOP compositions indicate a shift toward more woody vegetation during the event. These changes are concurrent with increased hydroclimate volatility as shown by carbon and calcium isotope proxies. Together, these records suggest that climate whiplash (oscillations between extreme wetness and aridity) and fire activity in California, both projected to increase with anthropogenic climate change, were tightly coupled during the early Holocene.

Little Ice Age flood events recorded in sag pond sediments in the Carrizo Plains National Monument, California

Nature Portfolio (Springer Nature) | March 8th, 2024

In California, severe precipitation events (SPEs) are often associated with winter season atmospheric rivers. These SPEs can generate hurricane-scale precipitation, creat

In California, severe precipitation events (SPEs) are often associated with winter season atmospheric rivers. These SPEs can generate hurricane-scale precipitation, creating a variety of natural hazards such as floods and landslides. For California, the most complete SPE-flood record yet generated is a 9000-year paleoflood reconstruction from the Santa Barbara Basin (Du et al. in Mar Geol 397:29–42, 2018). Finding terrestrial counterparts to compare to the Santa Barbara Basin is a challenge in Southern California where lake basins are rare and the terrestrial spatiotemporal signature of SPE floods remains largely unconstrained. Here, we present five 1–2 m sediment cores from a sag pond along the San Andreas Fault in the southern Carrizo Plain. The most complete record (core CLPC21-4) was selected for a variety of chronological, sedimentological, and biological analyses. Principal Component Analysis on these data reveals two end member sediment unit types: event versus ambient sedimentation. We focus on the two thickest sediment units likely generated by SPEs. These two units (EU 1 and EU 2) are especially distinct within CLPC21-4, characterized by erosive bases, above average sand content, normal grading, low magnetic susceptibility, and low total organic matter. Moreover, they are visually apparent across all five cores within the sag pond and thin from source to sink. Age control for the two units is constrained by AMS 14C dates on discrete organic materials and supported by the identification of Erodium’s first appearance ca. 1750–1765 CE in the Santa Barbara region. Using these age constraints, we infer the maximum limiting age range for Event Unit 1 from 1470 to 1640 CE and Event Unit 2 from 1740 to 1800 CE. Within the limits of dating, site-specific proxy sensitivities, and inherent meteorological heterogeneity, we propose a probable correlation to Santa Barbara Basin flood events at 1525 CE and 1760 CE. Our results suggest that sag ponds may represent a viable and untapped paleoclimatic archive for California. Future work will focus on a latitudinal series of sag ponds to determine the spatiotemporal sequence and correlativity of SPEs in the sediment record.

Local and synoptic mechanisms causing Southern California’s Santa Ana winds

Climate Dynamics (Springer) | August 25th, 2009

The cool, moist fall and winter climate in Southern Cali- fornia is often disrupted by dry, hot days with strong winds blowing out of the desert. These ‘‘Santa Ana’

The cool, moist fall and winter climate in Southern Cali- fornia is often disrupted by dry, hot days with strong winds blowing out of the desert. These ‘‘Santa Ana’’ winds are a dominant feature of the fall and wintertime climate of Southern California (Conil and Hall 2006), and have important human and ecological impacts. First, and most pronounced, is their effect on wildfires: following the hot, dry summer, the extremely low relative humidities and gusty strong winds that occur during Santa Anas introduce extreme fire risk which often culminates in wildfires with large economic loss.

Long-term climate and competition explain forest mortality patterns under extreme drought

Ecology Letters (Wiley) | December 20th, 2016

Rising temperatures are amplifying drought‐induced stress and mortality in forests globally. It remains uncertain, however, whether tree mortality across drought‐stri

Rising temperatures are amplifying drought‐induced stress and mortality in forests globally. It remains uncertain, however, whether tree mortality across drought‐stricken landscapes will be concentrated in particular climatic and competitive environments. We investigated the effects of long‐term average climate [i.e. 35‐year mean annual climatic water deficit (CWD)] and competition (i.e. tree basal area) on tree mortality patterns, using extensive aerial mortality surveys conducted throughout the forests of California during a 4‐year statewide extreme drought lasting from 2012 to 2015. During this period, tree mortality increased by an order of magnitude, typically from tens to hundreds of dead trees per km2, rising dramatically during the fourth year of drought. Mortality rates increased independently with average CWD and with basal area, and they increased disproportionately in areas that were both dry and dense. These results can assist forest managers and policy‐makers in identifying the most drought‐vulnerable forests across broad geographic areas.

Los Angeles Basin Stormwater Conservation Study: Task 3.1 Climate Change and Hydrologic Projections Appendices

U.S. Bureau of Reclamation (USBR) | October 1st, 2013

Reclamation’s Technical Service Center (TSC) performed Task 3.1 of the LA Basin Study—to develop and evaluate projected future climate conditions related to precipita

Reclamation’s Technical Service Center (TSC) performed Task 3.1 of the LA Basin Study—to develop and evaluate projected future climate conditions related to precipitation frequency over the Los Angeles Basin. The subtasks were to: Consider existing projections of climate change in the LA Basin Study area Determine appropriate climate scenarios for use in developing precipitation and potential evaporation input datasets to support subsequent hydrologic modeling Prepare data (hourly precipitation and potential evaporation) for input into the LACFCD’s Watershed Management Modeling System (WMMS) Determine storm event frequency for planning purposes The data, methods, and results from Task 3.1 are documented in this report. Results from these four subtasks were then transmitted to LACFCD, who used these results as input in their WWMMS as part of Task 3.2 of the LA Basin Study. LACFCD is preparing a companion report with the results from the hydrologic modeling.

Los Angeles Basin Stormwater Conservation Study: Task 3.2 Hydrologic Modeling Report

U.S. Bureau of Reclamation (USBR) | December 3rd, 2013

The Los Angeles County Flood Control District (LACFCD) partnered with the U.S. Department of the Interior, Bureau of Reclamation (Reclamation) to collaborate on t

The Los Angeles County Flood Control District (LACFCD) partnered with the U.S. Department of the Interior, Bureau of Reclamation (Reclamation) to collaborate on the Los Angeles Basin Stormwater Conservation Study (LA Basin Study). The purpose of the LA Basin Study is to investigate long-range water conservation and flood control impacts caused by projected changes in climate conditions and population in the Los Angeles region. The LA Basin Study will recommend potential modifications or changes in the operation of the existing stormwater capture systems, and the development of new facilities that could help resolve future water supply and flood control issues. These recommendations will be developed by identifying alternatives and conducting trade-off analyses. For Task 3, Downscaled Climate Change and Hydrologic Modeling of the LA Basin Study, Reclamation developed downscaled climate change projections, while LACFCD applied these projections to generate the future hydrology. LACFCD utilized the Watershed Management Modeling System (WMMS) to perform the hydrologic modeling for the LA Basin Study. This report summarizes the data, methods, and results of the historic and future hydrologic modeling. The purpose of Task 3.2, Hydrologic Modeling is to simulate hydrology with respect to climate change for the Los Angeles River, San Gabriel River, Ballona Creek, South Santa Monica Bay, North Santa Monica Bay, Malibu Creek, and Dominguez Channel/Los Angeles Harbor watersheds (Basin Study Watersheds). This study incorporates the entire watershed boundaries, including where they extend outside of Los Angeles County. The following sub-tasks were identified to achieve this objective: Historic Hydrologic Modeling (Water Year 1987 through 2000) Determine baseline scenario modeling assumptions Prepare WMMS to simulate baseline scenario Perform WMMS baseline simulations Analyze and summarize WMMS results Projected Hydrologic Modeling (Water Year 2012 through 2095) Determine future scenario modeling assumptions Prepare WMMS to simulate future scenarios Perform WMMS simulations Analyze and summarize WMMS results

Los Angeles Basin Stormwater Conservation Study: Task 4 Existing Infrastructure Response & Operations Guidelines Analysis

U.S. Bureau of Reclamation (USBR) | September 1st, 2014

The Los Angeles County Flood Control District (LACFCD) partnered with the U.S. Department of the Interior, Bureau of Reclamation (Reclamation) to collaborate on the Los A

The Los Angeles County Flood Control District (LACFCD) partnered with the U.S. Department of the Interior, Bureau of Reclamation (Reclamation) to collaborate on the Los Angeles Basin Stormwater Conservation Study (LA Basin Study). The purpose of the LA Basin Study is to investigate long-range water conservation and flood risk impacts caused by projected changes in climate conditions and population in the Los Angeles region. The LA Basin Study will recommend potential modifications or changes in the operation of the existing stormwater capture systems as well as the development of new facilities that could help resolve future water supply and flood risk issues. These recommendations will be developed by identifying alternatives and conducting trade-off analyses.  For Task 4, Existing Infrastructure Response and Operations Guidelines Analysis of the LA Basin Study, Reclamation, the U.S. Army Corps of Engineers (USACE), and the LACFCD jointly analyzed the major components of the water conservation and flood risk mitigation system. For the analysis, Reclamation assessed the 14 major LACFCD dams and reservoirs, USACE analyzed their 4 major flood control dams in the region, and LACFCD assessed the 26 major spreading grounds interconnected to the water conservation system. The LACFCD also evaluated 5 major channel outlets. This report summarizes the data, methods, and results of the existing infrastructure response to the historic climate and future projections.  The purpose of Task 4 is to assess the response of existing infrastructure and analyze the operation guidelines under both the current and future climate conditions. It is important to recognize that this effort relies upon the existing configuration of the water conservation and flood risk mitigation network as the baseline condition.  This evaluation includes a ranking assessment of the current and future stormwater volumes conserved or discharged, and other impacts to the water conservation and flood risk mitigation system. The following sub-tasks were identified to conduct this assessment:  Response to Current Climate (Water Year 1987 through 2000)  Analyze stormwater volumes conserved or discharged Analyze infrastructure response and operations guidelines  Response to Future Climate (Water Year 2012 through 2095) Analyze stormwater volumes conserved or discharged Analyze infrastructure response and operations guidelines The response to the current climate provided a representation of the existing situation and revealed how the existing infrastructure could reasonably be expected to perform under a historical climate to which the region has become accustomed. However, this may not be the case in the future. The response to future climate assessed the existing infrastructure under varying climate conditions to understand if it would function satisfactorily. This analysis of the existing infrastructure served as a status quo assessment of historical conditions as well as a “no action” evaluation of the future.  After the analysis of the historic and future climate conditions, an assessment was conducted for the system of dams and spreading ground facilities. A water conservation ranking—or performance level—was developed to assess the overall efficiency and resilience of the facilities to both the historic and projected future climate. Although results are assigned to the individual 18 dams/reservoirs and 26 spreading grounds, each facility was analyzed within the entire system. The dams and spreading grounds were ranked according to their performance with respect to one another; these rankings were used to develop the Task 4 performance levels.  Generally, facilities that were the least efficient resulted in being the least resilient to climate change and were assigned Performance Level III which has a high potential for enhancements. Facilities that were generally more efficient were more resilient to climate change and were assigned Performance Level II. Finally, facilities that were the most efficient tended to be the most resilient to climate change and were assigned to Performance Level I.  For the channel outlet analysis, assessment levels were developed to determine which of the five major channel outlets have the highest potential for increasing stormwater capture and reducing runoff to the Pacific Ocean. The ability to reduce the stormwater runoff that is lost to the ocean and capture it would greatly boost the potential stormwater supply in this region. The Task 4 analysis assigned assessment levels to the 5 major channel outlets and their respective watersheds.  The Los Angeles River ranked into Assessment Level III indicating that this watershed has the greatest potential for increasing stormwater supplies and should be targeted for future enhancements. For the remaining outlets, although these locations were found to have lower discharge volumes, additional capture efforts should still be targeted within these watersheds to further increase stormwater capture and improve local water supplies.