Atmospheric rivers in 20 year weather and climate simulations: A multi-model, global evaluation

American Geophysical Union (AGU) | June 1st, 2017

Atmospheric rivers (ARs) are narrow, elongated, synoptic jets of water vapor that play importantroles in the global water cycle and meteorological/hydrological extremes.

Atmospheric rivers (ARs) are narrow, elongated, synoptic jets of water vapor that play importantroles in the global water cycle and meteorological/hydrological extremes. Increasing evidence shows that ARs have signatures and impacts in many regions across different continents. However, global-scalecharacterizations of AR representations in weather and climate models have been very limited. Using a recently developed AR detection algorithm oriented for global applications, the representation of AR activities in multi-decade weather/climate simulations is evaluated. The algorithm is applied to 6-hourly(daily) integrated water vapor transport (IVT) from 22 (2) global weather/climate models that participated inthe Global Energy and Water Cycle Experiment Atmospheric System Study–Year of Tropical Convection Multimodel Experiment, including four models with ocean-atmosphere coupling and two models with super parameterization. Multiple reanalysis products are used as references to help quantify model errors inthe context of reanalysis uncertainty. Model performance is examined for key aspects of ARs (frequency,intensity, geometry, and seasonality), with the focus on identifying and understanding systematic errors insimulated ARs. The results highlight the range of model performances relative to reanalysis uncertainty inrepresenting the most basic features of ARs. Among the 17 metrics considered, AR frequency, zonal IVT, fractional zonal circumference, fractional total meridional IVT, and three seasonality metrics have consistently large errors across all models. Possible connections between AR simulation qualities and aspects of model configurations are discussed. Despite the lack of a monotonic relationship, the importance of model horizontal resolution to the overall quality of AR simulation is suggested by the evaluation results.

Attributing Extreme Events to Climate Change: A New Frontier in a Warming World

Cell Press | June 19th, 2020

The emerging field of extreme event attribution (EEA) seeks to answer the question: ‘‘Has climate change influenced the frequency, likelihood, and/or severity

The emerging field of extreme event attribution (EEA) seeks to answer the question: ‘‘Has climate change influenced the frequency, likelihood, and/or severity of individual extreme events?’’ Methodological advances over the past 15 years have transformed what was once an unanswerable hypothetical into a tractable scientific question—and for certain types of extreme events, the influence of anthropogenic climate change has emerged beyond a reasonable doubt. Several challenges remain, particularly those stemming from structural limitations in process-based climate models and the temporal and geographic limitations of historical observations. However, the growing use of large climate-model ensembles that capture natural climate variability, fine-scale simulations that better represent underlying physical processes, and the lengthening observational record could obviate some of these concerns in the near future. EEA efforts have important implications for risk perception, public policy, infrastructure design, legal liability, and climate adaptation in a warming world.

Attribution of declining western U.S. snowpack to human effects

American Meteorological Society (AMS) | December 1st, 2008

Observations show snowpack has declined across much of the western United States over the period 1950–99. This reduction has important social and economic impli

Observations show snowpack has declined across much of the western United States over the period 1950–99. This reduction has important social and economic implications, as water retained in the snowpack from winter storms forms an important part of the hydrological cycle and water supply in the region. A formal model-based detection and attribution (D–A) study of these reductions is performed. The detection variable is the ratio of 1 April snow water equivalent (SWE) to water-year-to-date precipitation (P), chosen to reduce the effect of P variability on the results. Estimates of natural internal climate variability are obtained from 1600 years of two control simulations performed with fully coupled ocean–atmosphere climate models. Estimates of the SWE/P response to anthropogenic greenhouse gases, ozone, and some aerosols are taken from multiple-member ensembles of perturbation experiments run with two models. The D–A shows the observations and anthropogenically forced models have greater SWE/P reductions than can be explained by natural internal climate variability alone. Model-estimated effects of changes in solar and volcanic forcing likewise do not explain the SWE/P reductions. The mean model estimate is that about half of the SWE/P reductions observed in the west from 1950 to 1999 are the result of climate changes forced by anthropogenic greenhouse gases, ozone, and aerosols.

Autumn precipitation: the competition with Santa Ana winds in determining fire outcomes in southern California

International Journal of Wildland Fire (CSIRO Publishing) | October 25th, 2022

California’s South Coast has experienced peak burned area in autumn. Following typically dry, warm summers, precipitation events and Santa Ana winds (SAWs) each occur w

California’s South Coast has experienced peak burned area in autumn. Following typically dry, warm summers, precipitation events and Santa Ana winds (SAWs) each occur with increasing frequency from autumn to winter and may affect fire outcomes. Aims. We investigate historical records to understand how these counteracting influences have affected fires. Methods. We defined autumn precipitation onset as the first 3 days when precipitation ≥8.5 mm, and assessed how onset timing and SAWs were associated with frequency of ≥100 ha fires and area burned during 1948–2018. Key results. Timing of autumn precipitation onset had negligible trend but varied considerably from year to year. A total of 90% of area burned in autumn through winter occurred from fires started before onset. Early onset autumns experienced considerably fewer fires and area burned than late onset autumns. SAWs were involved in many of the large fires before onset and nearly all of the lesser number after onset. Conclusions. Risk of large fires is reduced after autumn precipitation onset, but may resurge during SAWs, which provide high risk weather required to generate a large fire. Implications. During autumn before onset, and particularly during late onset autumns, high levels of preparation and vigilance are needed to avoid great fire impacts.

Benefit Accounting of Nature-Based Solutions for Watersheds

Pacific Institute | March 1st, 2021

Nature-based solutions (NBS) have the potential to combat pressing global problems, including climate change, water security and biodiversity loss. This guide builds on

Nature-based solutions (NBS) have the potential to combat pressing global problems, including climate change, water security and biodiversity loss. This guide builds on Benefit Accounting of Nature-Based Solutions for Watersheds Landscape Assessment (Shiao et al., 2020), which highlights the barriers for businesses to implement NBS at a large scale. The primary challenge for corporations is that there is no standardized method to identify, estimate and monitor the benefits that NBS can provide, making it hard to build the case for investments in these solutions.

Benefit Accounting of Nature-Based Solutions for Watersheds Guide - Version 2

Pacific Institute | August 23rd, 2023

This guide helps users account for and measure the stacked water,1 carbon, biodiversity and socio-economic benefits of a Nature-Based Solution NBS project. Accounting for

This guide helps users account for and measure the stacked water,1 carbon, biodiversity and socio-economic benefits of a Nature-Based Solution NBS project. Accounting for these benefits will improve a company’s impact reporting and help build the business case for green solutions, thereby supporting widespread investment, implementation and upscaling of NBS. This work will increase awareness of the value of NBS, not only for ecosystem health and community development, but also for companies directly.

Benefit-Cost Analysis of the Delta Conveyance Project

Berkeley Research Group (BRG) | May 16th, 2024

This report presents the results of a benefit-cost analysis for the Delta Conveyance Project (DCP), a plan to modernize the State Water Project (SWP)’s conveyance infra

This report presents the results of a benefit-cost analysis for the Delta Conveyance Project (DCP), a plan to modernize the State Water Project (SWP)’s conveyance infrastructure in the Sacramento-San Joaquin River Delta (Delta). The SWP plays a crucial role in supplying water resources to 27 million Californians. Businesses in the area served by the SWP produce $2.3 trillion in goods and services annually, making it the world’s eighth-largest economy. The SWP delivers an average of 2.56 million acre-feet of water annually to urban and agricultural customers in the Bay Area, Central Valley, Central Coast, and Southern California. However, by 2070, climate change and sea-level rise are expected to reduce SWP deliveries by approximately 22%, or 546 thousand acre-feet per year (TAF/yr). In addition, the SWP faces an ongoing risk of service disruptions following seismic events near the Delta; these events could cause outages and reduce the quality of water exports from the SWP south of the Delta.

Big Ag, Big Oil, and the California Water Crisis

Food and Water Watch (FWW) | February 1st, 2023

Climate change is wreaking havoc on California’s water stability. The state is mired in long- term drought, punctuated by relatively brief periods of extreme precipitat

Climate change is wreaking havoc on California’s water stability. The state is mired in long- term drought, punctuated by relatively brief periods of extreme precipitation and catastroph- ic flooding. But the impacts of climate change on state water supplies only tell part of the story. Most of California’s water goes not for individual use, but instead to corporate agricul- tural and fossil fuel interests (Big Ag and Big Oil). These users reap tremendous profits, while more than 1 million Californians lack access to clean water.

Building Ecological Resilience in Highly Modified Landscapes

BioScience (Oxford University Press) | November 7th, 2018

Ecological resilience is a powerful heuristic for ecosystem management in the context of rapid environmental change. Significant efforts are underway to improve

Ecological resilience is a powerful heuristic for ecosystem management in the context of rapid environmental change. Significant efforts are underway to improve the resilience of biodiversity and ecological function to extreme events and directional change across all types of landscapes, from intact natural systems to highly modified landscapes such as cities and agricultural regions. However, identifying management strategies likely to promote ecological resilience remains a challenge. In this article, we present seven core dimensions to guide long-term and large-scale resilience planning in highly modified landscapes, with the objective of providing a structure and shared vocabulary for recognizing opportunities and actions likely to increase resilience across the whole landscape. We illustrate application of our approach to landscape-scale ecosystem management through case studies from two highly modified California landscapes, Silicon Valley and the Sacramento–San Joaquin Delta. We propose that resilience-based management is best implemented at large spatial scales and through collaborative, cross-sector partnerships.

Building water resilience in the face of cascading wildfire risks

American Association for the Advancement of Science (AAAS) | September 15th, 2023