Rapid vegetation redistribution in Southern California during the early 2000s drought

American Geophysical Union (AGU) | August 31st, 2012

Climate change in semi-arid, midlatitude mountain environments is expected to shift the spatial patterns of temperature, water availability, and vegetation upslope. Veg

Climate change in semi-arid, midlatitude mountain environments is expected to shift the spatial patterns of temperature, water availability, and vegetation upslope. Vegetation growing near its low-elevation range limit may prove especially vulnerable to mortality and decline. We investigated the altitudinal pattern of conifer mortality that occurred from 2002 to 2004 in Southern California’s San Jacinto Mountains. We found that conifer mortality was focused in the lower portion of the midmontane conifer range, which drove the midmontane conifer distribution upslope. We investigated past reports of conifer mortality in Southern California by searching historical newspaper accounts. We found evidence of previous episodes of conifer mortality that coincided with past droughts, and which may have caused vegetation redistribution in the past. We interpret the early2000s mortality and associated vegetation redistribution as a response to natural decadal tocentennial climate variability. Moreover, we hypothesize this response mode will dominatethe early impact of global climate change on semi-arid forest, which, in turn, may complicate efforts to distinguish between ecological changes attributable to natural climate variability and those attributable to global climate change.

Recent warming of landfalling atmospheric rivers along the west coast of the United States

American Geophysical Union (AGU) | May 30th, 2019

Abstract: Atmospheric rivers (ARs) often generate extreme precipitation, with AR temperature strongly influencing hydrologic impacts by altering the timing and magni

Abstract: Atmospheric rivers (ARs) often generate extreme precipitation, with AR temperature strongly influencing hydrologic impacts by altering the timing and magnitude of runoff. Long‐term changes in AR temperatures therefore have important implications for regional hydroclimate—especially in locations where a shift to more rain‐dominated AR precipitation could affect flood risk and/or water storage in snowpack. In this study, we provide the first climatology of AR temperature across five US West Coast sub‐regions. We then assess trends in landfalling AR temperatures for each sub‐region from 1980 to 2016 using three reanalysis products. We find AR warming at seasonal and monthly scales. Cool‐season warming ranges from 0.69°C to 1.65°C over the study period. We detect monthly‐scale warming of >2°C, with the most widespread warming occurring in November and March. To understand the causes of AR warming, we quantify the density of AR tracks from genesis to landfall, and analyze along‐track AR temperature for each month and landfall region. We investigate three possible influences on AR temperature trends at landfall: along‐track temperatures prior to landfall, background temperatures over the landfall region, and AR temperature over the coastal ocean adjacent to the region of landfall. Generally, AR temperatures at landfall more closely match coastal and background temperature trends than along‐track AR temperature trends. The seasonal asymmetry of the AR warming and the heterogeneity of influences have important implications for regional water storage and flood risk—demonstrating that changes in AR characteristics are complex, and may not be directly inferred from changes in the background climate. Plain Language Summary: Atmospheric river (AR) storms are well known for their ability to accumulate snowpack, provide drought relief, and generate extreme precipitation and flooding along the West Coast of the United States. AR temperature is an important variable for determining the water resource impacts of a given event, such as the ratio of rain to snow delivered by an individual storm. As a result, changes in AR temperature have implications for both water storage and flood risk. We find substantial warming in ARs at both the seasonal and monthly scales, as well as seasonal and regional variations in the amount of warming along the US West Coast. To understand the warming of ARs at the landfall regions, we compare these monthly temperature trends with trends in temperature along the AR tracks, background temperature over the landfall region, and temperature over the coastal ocean adjacent to the landfall region. The most robust warming occurs in November and March, which has important implications for increased regional flood risk and decreased water storage, and motivates further investigation in other AR‐prone regions around the globe.

Regional Governance of Flood Management in the Central Valley

California Department of Water Resources (DWR) | May 30th, 2014

California faces significant challenges in managing its highly variable water resources, particularly as climate change and a growing population exacerbate drought and fl

California faces significant challenges in managing its highly variable water resources, particularly as climate change and a growing population exacerbate drought and flood risks.  The California Department of Water Resources (DWR) and other state agencies have been encouraging integrated approaches to water management, taking into account the connections between water supply, water quality, flood protection, and ecosystem health. The recent California Water Action Plan calls for improved coordination between local, state and federal agencies and tribal governments in order to develop multi-­benefit water management strategies. Regional-­scale planning has become a crucial avenue for advancing these efforts. Initiated in 2002, the Integrated Regional Water Management Planning (IRWM) process has led to the formation of 48 water planning regions statewide, in which diverse local agencies have developed integrated plans for managing all aspects of a region’s water management. More recently, a Regional Flood Management Planning (RFMP) process was created in the context of the Central Valley Flood Protection Plan to advance integrated approaches to reducing flood risks. Six flood planning regions, overlapping with nine IRWM regions, were formed in 2012. This study analyzes the origins and functioning of the IRWM and RFMP processes, and the degree of coordination between them to address flood risks in the Central Valley. In particular, it examines how each is working to generate multi-­benefit strategies, and how they account for climate change. It also discusses opportunities for future coordination between the IRWM and RFMP processes, and DWR’s role in supporting this. This study is primarily based upon an analysis of publicly available documents related to the IRWM and RFMP processes. It is also informed by meeting observations and conversations with staff at DWR and the Central Valley Flood Protection Board, and participants in IRWM and RFMP processes. Since RFMPs were not yet completed at the time of this writing, this study’s findings are preliminary. Nonetheless, this report provides an indication of the overall functioning of these RFMP and IRWM regions, and some general considerations for DWR as it assesses next steps in supporting these programs.

Report Card for California's Infrastructure 2019

American Society of Civil Engineers (ASCE) | May 9th, 2019

Resilient landscape vision for Lower Walnut Creek

San Francisco Estuary Institute (SFEI) | November 30th, 2016

Lower Walnut Creek (Contra Costa County, CA) and its surrounding landscape have undergone considerable land reclamation and development since the mid-nineteenth century.

Lower Walnut Creek (Contra Costa County, CA) and its surrounding landscape have undergone considerable land reclamation and development since the mid-nineteenth century. In 1965, the lower 22 miles of Walnut Creek and the lower reaches of major tributaries were converted to flood control channels to protect the surrounding developed land. In the recent past, sediment was periodically removed from the lower Walnut Creek Flood Control Channel to provide flow capacity and necessary flood protection. Due to the wildlife impacts and costs associated with this practice, the Contra Costa County Flood Control and Water Conservation District (District) is now seeking a new channel management approach that works with natural processes and benefits people and wildlife in a cost-effective manner. Flood Control 2.0 project scientists and a Regional Science Advisory Team (RSAT) worked with the District to develop a long-term management Vision for lower Walnut Creek that could result in a multi-benefit landscape that restores lost habitat and is resilient under a changing climate. Development of the Vision began with technical analyses focused on understanding past and present landscape functioning and the changes to key processes and landscape features over the past 150 to 200 years. The key findings from these analyses include the following: • Landscape change – During the mid-19th century, lower Walnut Creek was surrounded by a continuous expanse of tidal wetlands occupying approximately 5,000 acres. Perennial freshwater marsh, willow thicket, and alkali meadow formed a large non-tidal wetland complex that adjoined the tidal marsh on its southern end. Over the past century and a half, the non-tidal wetland complex has been lost completely and the tidal wetland area has decreased by 40%. The remaining marsh areas are highly fragmented and cut-off from Walnut Creek by engineered levees. The loss of tidal wetland area has resulted in a substantial decrease in tidal prism and contributed to current in-channel sediment accumulation issues. Around the mouth of Walnut Creek, sediment accumulation has caused the position of the shoreline to expand into the Bay by up to half a mile. • Sediment accumulation – Since 1965, approximately 1.4M cubic yards of sediment have been removed from lower Walnut Creek, with approximately 70% coming from the tidal zone downstream of head of tide (i.e., the inland extent of tidal inundation at mean higher high water). Repeat channel cross-section surveys indicate that the channel quickly fills in with sediment following dredging events (due in large part to decreased tidal prism and associated channel scour capacity) and that the channel bed elevation is currently at or near “quasi-equilibrium.” A channel sediment budget for 1965-2007 indicates that approximately 80% of the watershed-derived sediment made it through lower Walnut Creek and out to the Bay, while the remaining 20% was likely deposited directly following channel construction and subsequent dredging events.

Resilient Landscape Vision for Lower Walnut Creek: Baseline Information and Management Strategies

San Francisco Estuary Institute (SFEI) | November 1st, 2016

Lower Walnut Creek (Contra Costa County, CA) and its surrounding landscape have undergone considerable land reclamation and development since the mid-nineteenth century.

Lower Walnut Creek (Contra Costa County, CA) and its surrounding landscape have undergone considerable land reclamation and development since the mid-nineteenth century. In 1965, the lower 22 miles of Walnut Creek and the lower reaches of major tributaries were converted to flood control channels to protect the surrounding developed land. In the recent past, sediment was periodically removed from the lower Walnut Creek Flood Control Channel to provide flow capacity and necessary flood protection. Due to the wildlife impacts and costs associated with this practice, the Contra Costa County Flood Control and Water Conservation District (District) is now seeking a new channel management approach that works with natural processes and benefits people and wildlife in a cost-effective manner. Flood Control 2.0 project scientists and a Regional Science Advisory Team (RSAT) worked with the District to develop a long-term management Vision for lower Walnut Creek that could result in a multi-benefit landscape that restores lost habitat and is resilient under a changing climate. 

Resilient Landscape Vision for the Calabazas Creek, San Tomas Aquino Creek, and Pond A8 Area: Bayland-Creek Reconnection Opportunities

San Francisco Estuary Institute (SFEI) | May 1st, 2018

This report proposes a multi-faceted redesign of the South San Francisco Bay shoreline at the interface with Calabazas and San Tomas Aquino creeks. Recognizing the opport

This report proposes a multi-faceted redesign of the South San Francisco Bay shoreline at the interface with Calabazas and San Tomas Aquino creeks. Recognizing the opportunities presented by changing land use and new challenges, such as accelerated sea-level rise, we explore in this report a reconfigured shoreline that could improve ecosystem health and resilience, reduce maintenance costs, and protect surrounding infrastructure. 

Resilient Landscape Vision for Upper Penitencia Creek

San Francisco Estuary Institute (SFEI) | January 1st, 2019

This report proposes a new multi-benefit approach to flood management along Upper Penitencia Creek. Recognizing the creek’s complex history, land use, and challenges, t

This report proposes a new multi-benefit approach to flood management along Upper Penitencia Creek. Recognizing the creek’s complex history, land use, and challenges, this report explores a suite of actions that could help meet flood management objectives while improving ecosystem functioning, expanding recreational opportunities, and supporting water supply needs. 

Responses and impacts of atmospheric rivers to climate change

Nature Portfolio (Springer Nature) | March 9th, 2020

Atmospheric rivers (ARs) are characterized by intense moisture transport, which, on landfall, produce precipitation which can be both beneficial and destructive. ARs in C

Atmospheric rivers (ARs) are characterized by intense moisture transport, which, on landfall, produce precipitation which can be both beneficial and destructive. ARs in California, for example, are known to have ended drought conditions but also to have caused substantial socio-economic damage from landslides and flooding linked to extreme precipitation. Understanding how AR characteristics will respond to a warming climate is, therefore, vital to the resilience of communities affected by them, such as the western USA, Europe, East Asia and South Africa. In this Review, we use a theoretical framework to synthesize understanding of the dynamic and thermodynamic responses of ARs to anthropogenic warming and connect them to observed and projected changes and impacts revealed by observations and complex models. Evidence suggests that increased atmospheric moisture (governed by Clausius–Clapeyron scaling) will enhance the intensity of AR-related precipitation — and related hydrological extremes — but with changes that are ultimately linked to topographic barriers. However, due to their dependency on both weather and climate-scale processes, which themselves are often poorly constrained, projections are uncertain. To build confidence and improve resilience, future work must focus efforts on characterizing the multiscale development of ARs and in obtaining observations from understudied regions, including the West Pacific, South Pacific and South Atlantic.

Retrofitting Sustainable Urban Drainage Systems (SuDS): A Cost-Benefit Analysis Appraisal

Water (MDPI) | August 16th, 2022

Sustainable Urban Drainage Systems (SuDS) are known to help mitigate flooding whilst simultaneously delivering other positive outcomes, such as the provision of environme

Sustainable Urban Drainage Systems (SuDS) are known to help mitigate flooding whilst simultaneously delivering other positive outcomes, such as the provision of environmental, economic, educational, and business benefits. Despite this, there has been a relatively low uptake of SuDS in new developments and even less of an uptake in the opportunities for retrofitting SuDS in existing buildings. A major barrier to uptake has been a lack of understanding regarding the value of the benefits provided by SuDS. This study presents an appraisal of the costs and benefits derived from the retrofitting of SuDS in existing buildings and reveals some of the key decision-making considerations during the design and installation of such schemes. A qualitative research approach that included a number of case studies of successfully retrofitted SuDS schemes within public buildings was conducted. A novel feature of the research was the use of the Willingness to Pay (WTP) approach to value the tangible and intangible benefits provided by the various schemes from the perspectives of the property owners. The findings revealed that the retrofit provided a net value to the client of over £100,000 over 10 years, a mean CBA ratio of 5.3/10, and a return on investment (ROI) that would be achieved in less than 3 years. The importance of stakeholder engagement during the decision-making process was highlighted in helping to overcome many of the design, installation, and maintenance challenges. The findings demonstrate a significant ROI for these SuDs retrofit schemes and highlight useful approaches to overcoming the barriers in valuing the importance of the intangible benefits. In supporting the uptake of the retrofitting of SuDS, it is recommended that these benefits are given full consideration by property owners, urban planners, and architects during the design of retrofit schemes and throughout the decision-making stage.