Author: cw3e-web

CW3E Publication Notice: Antecedent Snowpack Cold Content Alters the Hydrologic Response to Extreme Rain-on-Snow Events

CW3E Publication Notice

Antecedent Snowpack Cold Content Alters the Hydrologic Response to Extreme Rain-on-Snow Events

December 4, 2023

A new paper titled “Antecedent Snowpack Cold Content Alters the Hydrologic Response to Extreme Rain-on-Snow Events” by Lisa Katz (University of Nevada, and now CW3E), Gabriel Lewis (University of Nevada, and now CW3E), Sebastian Krogh (University of Concepción), Stephen Drake (University of Nevada), Erin Hanan (University of Nevada), Benjamin Hatchett (University of Nevada/Desert Research Institute), and Adrian Harpold (University of Nevada) was recently published in the Journal of Hydrometeorology. This paper examines rain-on-snow (ROS) events in California’s Sierra Nevada, focusing on the controls that antecedent snowpack conditions, namely snowpack cold content, snow density, snow water equivalent (SWE), and liquid water content, have on the timing and magnitude of liquid drainage from the snowpack onto the land surface. By furthering our understanding of how hydrometeorological models interpret meteorological and watershed interactions during complex events such as ROS, this work advances CW3E’s 2019–2024 Strategic Plan goal to improve modeling capabilities to better serve water supply management programs in the western U.S., such as Forecast Informed Reservoir Operations (FIRO) and flood warning systems.

The researchers modeled 71 ‘historical’ ROS events between 1981 and 2019 true to the record, and created ‘scenario’ events for modeling, by exposing a set of 40 unique snowpack states to meteorological conditions from the most extreme ROS. The model used was the physically based, 1-dimensional SNOWPACK, initiated with the Richards Equation. Results from this study agreed with previous studies that rainfall is the dominant control on TWI during ROS (R2 = 0.95, p < 0.01), and found that terrestrial water input (TWI) is largely generated at higher elevations, where rainfall amount is greatest. This study adds that snowpacks with more negative cold content reduce the ratio of TWI to rain over the event duration. Scenario event TWI to rain ratio responses spanned the range from ≤ 1 to > 1, providing evidence for snowpacks storing rain or meltwater, depending on antecedent snowpack conditions.

An analysis of antecedent snowpack conditions by multiple linear regression (R2 = 0.92, p < 0.01) determined that cold content, over snow density, liquid water content, or SWE, produced the highest Pearson correlation with TWI (0.75, p < 0.01), and even stronger relationships were found for cold content–liquid water content (0.89, p < 0.01) and cold content–density (0.81, p < 0.01). These results suggest that refreezing from higher cold content and slower unsaturated flow from higher snow density lead to more liquid water retention during ROS events.

Antecedent cold content is a rarely measured snowpack state that is the result of several interconnected snowpack processes and could lead to useful observations for streamflow forecasting. A combination of refreezing, matric forces, or reductions in hydraulic conductivity from dense vertical layering may cause the larger retention of rainfall and/or TWI than would be predicted by a simple refreezing of the snowpack in a single snow layer. This retention may be partially due to rainfall and cold content being larger at the higher elevations, affecting the catchment average. Results from this study highlight the importance of hydraulic limitations in dense snowpacks and energy limitations in warm snowpacks for retaining liquid water that would otherwise be available as TWI for flooding.

Figure 1: (Figure 6 from Katz et al. 2023) Scenario analysis of 1986 ROS event at High falling (top) on the cold and dry antecedent snowpack conditions from 26 Jan 2005 and (middle) the warm and wet antecedent snowpack conditions from 26 Jan 2000. The upper panels show hourly rain and precipitation (bars) as well as resulting TWI (black). (bottom) Cumulative TWI from 2000 (blue) and 2005 (red) antecedent conditions. Dashed vertical lines indicate the ROS event start and end.

Katz, L., Lewis, G., Krogh, S., Drake, S., Hanan, E., Hatchett, B., & Harpold, A. (2023). Antecedent Snowpack Cold Content Alters the Hydrologic Response to Extreme Rain-on-Snow Events. Journal of Hydrometeorology, 24(10), 1825-1846. https://doi.org/10.1175/JHM-D-22-0090.1

CW3E AR Update: 1 December 2023 Outlook

CW3E AR Update: 1 December 2023 Outlook

December 1, 2023

Click here for a pdf of this information. Click here to provide feedback on these outlooks!

Trio of Atmospheric Rivers Forecast to Impact Pacific Northwest

  • An AR associated with a cold storm will bring a brief period of AR conditions tonight into Saturday
  • Two stronger ARs are forecast to make landfall late Sat 2 Dec and early Mon 4 Dec
  • AR1 conditions (based on Ralph et al. 2019 AR scale) are forecast during the first AR
  • Nearly all GEFS ensemble members are forecasting an AR4 over northern coastal OR due to a prolonged period (> 72 hours) of continuous AR conditions during the second and third ARs
  • A majority of ECMWF EPS members are forecasting a break in AR conditions between the second and third ARs, with AR2/3 conditions likely during the second AR, and AR3/4 conditions likely during the third AR
  • The NWS Weather Prediction Center (WPC) is currently forecasting 7-day precipitation totals ≥ 10 inches in the vicinity of the Olympic Mountains, Cascades, and Coast Ranges
  • The NWS WPC Extreme Rainfall Outlook highlights a Marginal Risk for flooding for western OR/WA Dec 2-6 with a Slight Risk for the Olympic Peninsula on Dec 5
  • Heavy rain, particularly during the second and third ARs, is expected to cause flooding on rivers in western WA and northwestern OR
  • Rain falling on fresh snowpack will likely increase flood risk near the Olympic Mountains and WA Cascades
  • NWS Seattle and Portland are forecasting at least 1-3 feet of snow in the Olympic Mountains and the Cascades through late Saturday evening
  • High snowfall totals in the forecast have led to major to extreme conditions forecast within the NWS Winter Storm Severity Index along the Cascades between 1-3 December

Click images to see loops of GFS IVT and IWV forecasts

Valid 1200 UTC 01 December 2023 – 1800 UTC 6 December 2023


 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Summary provided by M. Steen, S. Bartlett, C. Castellano and P. Iniguez; 1 December 2023

To sign up for email alerts when CW3E post new AR updates click here.

*Outlook products are considered experimental

Breaking Ground to Expand Climate Monitoring Network in Upper Yampa River Basin

Breaking Ground to Expand Climate Monitoring Network in Upper Yampa River Basin

November, 28 2023

Building on a successful pilot study, two new climate monitoring stations will expand the coverage of the monitoring network and improve understanding of climate and water resources in the Yampa River Basin.

Steamboat Springs, Co., (November 27, 2023) – In early November 2023, two new climate monitoring stations were installed in the Upper Yampa River Basin. The first is on private property at the Howe Ranch, roughly 10 miles North of Hayden, CO, and the second is on private property roughly 7 miles northwest of Steamboat Springs, CO. The installations represent the breaking of ground for a new phase of collaboration between Yampa Valley Sustainability Council (YVSC), Colorado Mountain College (CMC), and the Center for Western Weather and Water Extremes (CW3E) at Scripps Institution of Oceanography at the University of California San Diego. The project team conducted a successful pilot installation near Stagecoach Reservoir in 2022 and is now working on expanding the network of monitoring stations thanks to additional funding from the Upper Yampa Water Conservancy District (UYWCD), the Colorado River District’s (CRD) Community Funding Partnership, and the Colorado Water Conservation Board’s (CWCB) Water Plan Grant.

Left: The newly installed ELK station overlooking Elk Mountain, near Steamboat Springs, amid a light snow flurry. Right: The ELK soil pit prior to backfilling, showing the soil temperature/moisture sensors.

The climate monitoring network is motivated by increasing uncertainty in“snow-to-flow” predictions of water availability in the Colorado River Basin. Water managers are finding it harder to predict how much snowmelt runoff will enter rivers and reservoirs in the Colorado River Basin, and one theory is that drier soils are absorbing snow melt like a sponge. The hypothesis is that warming temperatures in recent years are causing soils to dry out and winter snowfall to sublimate or evaporate away, leading to reduced springtime run-off. Unfortunately, without reliable measurements of soil moisture and meteorological conditions throughout the basin, the “soil drying” hypothesis has been difficult to test. “Soil moisture is an under-observed reservoir of water in the basin” says Dr. Marty Ralph, the Director of CW3E and principal investigator on the project. The new monitoring stations were designed to rectify this problem by providing the much-needed observations of soil moisture and a baseline for long-term monitoring in the basin. Ralph’s vision for the project is to “develop methods to comprehensively reduce the uncertainty in that knowledge gap” by integrating the new data into forecasting and water management decision-making.

Left: CW3E, CMC, and YVSC team members assemble the tower for the meteorological sensors at ELK station.
Center: Team members work to install the meteorological sensors on the HOW station tower, with soil from the soil pit laid out in foreground. Right: Team members work to install the HOW soil sensors and backfill the soil pit.

The new stations record soil temperature and moisture at six different depths down to 40 inches in the soil profile. The stations also include meteorological sensors measuring wind speed and direction, precipitation, snow depth, temperature, relative humidity, pressure, and solar radiation. Thanks to cellular communications, the data are available in near-real-time. Site locations were identified using a comprehensive geospatial analysis designed to maximize the impact of their observations and capture basin land surface complexity. First, the team analyzed spatial patterns in the various characteristics that drive soil moisture variability such as precipitation, topography, and vegetation cover. They then compiled records of all the existing soil and meteorological observations in the watershed to identify observational gaps in the basin. Gaps in the existing observations were confirmed by input from local stakeholders, water managers, forecasting agencies, and researchers and site locations were finalized. The newly installed and existing stations will be complemented by an additional six stations to be installed through 2026, resulting in a comprehensive network spanning the entire basin.

Widespread enthusiasm for the project is evident in the Yampa Valley. Executive Director of YVSC, Dr. Michelle Stewart, says “the Yampa Valley Sustainability Council sees this ground-breaking for the climate monitoring network expansion as critical in enhancing our ability to accurately monitor and respond to climate change in the Yampa Valley. YVSC greatly appreciates the investment and support from our funding partners to further this type of science-driven, decision-support project for the benefit of water and land use in the Yampa River Basin.”

Andy Rossi, the General Manager of UYWCD, adds that “the continued expansion of a soil moisture monitoring network across the Upper Yampa River Basin is critical to understanding spring runoff, especially as our climate becomes hotter and drier.” He also sees potential for benefits outside the basin, explaining that “the data collected from these stations will not only assist local water managers like UYWCD, but could lead to a more collaborative approach to water management decisions downstream.” The support from UYWCD, CRD and CWCB has been critical in continuing this effort to increase observational monitoring in the Upper Yampa.

Amy Moyer, Director of Strategic Partnerships at the Colorado River District, also recognizes the importance of the project. “In coordination with related efforts across our District, we see this climate and soil monitoring effort as an important piece of an overall strategy to better understand how water resources are changing in the Colorado River Basin, both from near-term operations and to long term planning perspectives.” She also praised the project for its commitment to community-oriented science, adding that “the project aligns well with our Community Funding Partnership Program goals, and we are proud to financially support this cooperative initiative that will achieve multiple benefits.”

To maximize the impact of the knowledge generated by the monitoring network, the project team is committed to collaborating with the residents and water interests of the Yampa River Basin. This involves partnering with local private landowners to host the stations, inviting students and volunteers from Colorado Mountain College to participate in the installations, and co-organizing the Yampa Basin Rendezvous–a conference dedicated to water and weather in the Yampa River Basin held at Colorado Mountain College in late spring each year, as well as coordinating with related regional and federal soil monitoring efforts.

Local partners Emily Howe and Jeremiah Psiropoulos described their motivation for participating in the project and the benefits they see for the community: “We are hosting this station to help provide a better understanding of how water behaves in the Elkhead watershed. As biologists ourselves, we’re excited to contribute data to scientists working to understand hydrology and climate change in our community, and we love the idea of helping to maintain a long-term dataset. We manage the Howe Ranch to conserve the land, water, flora, and fauna in our community. As water scarcity and drought accelerate in the Yampa Valley along with a warmer future, we hope that water use in our valley will be data informed and sustainable, and we hope our weather station will benefit efforts to ensure that.”

Nathan Stewart, Professor of Ecosystem Science at CMC and project collaborator, recognizes the value of the Climate Monitoring Network to undergraduate training in STEM: “our students participate in station installation alongside technical experts from CW3E, colleagues from YVSC, and local Yampa Valley landowners and witness dynamic community-engaged science first hand. Immediate benefits include mentorship in tower, sensor, and soil pit establishment; long term benefits include training in station maintenance, data analysis and visualization, and science communication. The network provides our basin with an unparalleled outdoor laboratory for student career training in meteorology and watershed science.”

This season’s station installations represent the groundbreaking of the newly funded expansion of the monitoring network. Expanding the network will generate additional observations and sample a wider range of soil and hydrological conditions, helping water managers to better determine exactly what is happening to snowpack in the basin and improve predictions of springtime reservoir inflows.

The data collected by the stations will be publicly available on the CW3E website, MesoWest, and the NOAA Physical Science Laboratory.

Contact:

El Knappe

Center for Western Weather and Water Extremes

Phone: 805-708-7472

Email: eknappe@ucsd.edu

Madison Muxworthy

Yampa Valley Sustainability Council

Phone: 970-871-9299, ext. 107

Email: madison@yvsc.org

Nathan Stewart

Colorado Mountain College

Phone: 970-870-4562

Email: nlstewart@coloradomtn.edu

CW3E AR Update: 28 November 2023 Outlook

CW3E AR Update: 28 November 2023 Outlook

November 28, 2023

Click here for a pdf of this information. Click here to provide feedback on these outlooks!

Multiple Atmospheric Rivers Forecast to Impact Pacific Northwest and Northern California

  • Several low pressure systems will spin out of the Asian continent and into the Northeast Pacific Ocean heading into the weekend.
  • As these systems approach the West Coast of North America, multiple atmospheric rivers (ARs) are forecast to develop and make landfall over the Pacific Northwest.
  • The first AR is forecast to arrive by Sat Dec 2, with two stronger ARs to follow on Sun Dec 3 possibly through Wed Dec 6. IVT values may exceed 750 kg/(ms) with the third AR.
  • While there is high confidence on the development of the ARs, large uncertainty in the timing, duration, and intensity remain.
  • Moderate/heavy precipitation is very likely from far northwest CA into southern BC.
  • Rises on area rivers could push them above action stage or even flood stage.
  • Freezing levels may initially fall to ~2000’ in northern WA and to 5000’ in central CA during the first (weak) AR before rising with subsequent ARs.
  • Significant mountain snow is possible.

Click images to see loops of GFS IVT and IWV forecasts

Valid 1200 UTC 28 November 2023 – 0000 UTC 6 December 2023


 

 

 

 

 

 

 

 

 

 

 

 

 

 

Summary provided by P. Iniguez, C. Castellano, and S. Bartlett; 28 November 2023

To sign up for email alerts when CW3E post new AR updates click here.

*Outlook products are considered experimental

CW3E Welcomes Lu Su

CW3E Welcomes Lu Su

November 20, 2023

Lu Su joined CW3E in November 2023 as a postdoctoral research scholar. Prior to joining the Center, Lu Su earned her PhD in Geography from University of California, Los Angeles, under the supervision of Dr. Dennis P. Lettenmaier. Lu’s doctoral dissertation explored the evaluation and improvement of hydrological simulation and forecast in the western U.S..Her work primarily focused on three areas: improving subseasonal drought onset and termination forecast accuracy using NOAA’s Climate Testbed Subseasonal Experiment (SubX) reforecasts, evaluating and improving flood forecasting capabilities of the Noah-MP model and comparing with the the existing river forecast center predictions, and developing finely calibrated parameters for two prominent land surface models – the VIC model and Noah-MP.

Additionally, Lu’s research extends to historical drought analysis over the past century in the contiguous United States, and the creation of a gridded forcing dataset and conducting over ten high-resolution climate simulations using the VIC model in California.

At CW3E, Lu will be working with the hydrology group under the supervision of Dr. Ming Pan. Her work will involve supporting the development and operation of CW3E’s hydrologic monitoring and seasonal forecasting system; performing hydrologic modeling experiments and analysis for the verification and improvement of forecast skills; and conducting climate-scale modeling to investigate the hydrologic consequences of climate change in the California region and its impact on regional water resources and other sectors.

CW3E Publication Notice: A long short-term memory neural network-based error estimator for three-dimensional dynamically adaptive mesh generation

CW3E Publication Notice

A long short-term memory neural network-based error estimator for three-dimensional dynamically adaptive mesh generation

November 20, 2023

A new paper titled “A long short-term memory neural network-based error estimator for three-dimensional dynamically adaptive mesh generation” by Xiaofei Wu (CUIT, China), Pu Gan (CUIT, China), Jinxi Li (IAP, CAS), Fangxin Fang (ICL, UK), Jerry Zou (CW3E), Christopher Pain (ICL, UK), Xiao Tang (IAP, CAS), Jinyuan Xin (IAP, CAS), Zifa Wang (IAP, CAS), and Jiang Zhu (IAP, CAS) was recently published in the Physics of Fluids. This study introduces a LSTM neural network for guiding mesh adaptation in atmospheric modeling. The LSTM neural network model is integrated into the existing unstructured mesh atmosphere model to generate adaptive meshes in both time and space for 2D/3D scenarios. This constitutes an initial phase toward establishing a comprehensive neural network for 3D unstructured adaptive mesh generation. This work supports the Modeling Capabilities for the Western United States priority area in CW3E’s 2019–2024 Strategic Plan.

In this study, we harness the innovative power of a long short-term memory (LSTM) neural network as an error estimator for adapting unstructured meshes in both 2D and 3D scenarios. This LSTM network predicts the evolution of the adaptive grid based on specified variables, presenting itself as an artificial intelligence-driven architecture to optimize the adaptive criterion for the target variable. Our findings reveal that the mesh patterns generated by the LSTM error estimator within 3D adaptive atmospheric model Fluidity-Atmosphere closely resemble those produced by traditional error estimators, highlighting superior performance in enhancing simulation accuracy. Notably, with an increase in the number of nodes, the LSTM mesh generator significantly reduces CPU time requirements by up to 50% in 3D cases compared to the conventional mesh generator within Fluidity-Atmos, showcasing its remarkable computational efficiency.

Adaptive meshes play a pivotal role in numerical weather modeling, providing an efficient, precise, and flexible representation of intricate physical phenomena. The potential application of adaptive meshes holds promise for improving predictions of high-impact weather systems that require high-resolution simulations at a reasonable cost.

Figure 1: The proposed LSTM neural network for mesh adaptivity (a), the LSTM memory cell in this architecture (b), and the schematic of input data selection criteria (c).

Wu, X., Gan, P., Li, J., Fang, F., Zou, X., Pain, C. C., Tang, X., Xin, J., Wang, Z., & Zhu, J. (2023). A long short-term memory neural network-based error estimator for three-dimensional dynamically adaptive mesh generation. Physics of Fluids, 35(10), 106610. https://doi.org/10.1063/5.0172020

CW3E Publication Notice: Mesoscale and Synoptic Scale Analysis of Narrow Cold Frontal Rainband During a Landfalling Atmospheric River in California During January 2021

CW3E Publication Notice

Mesoscale and Synoptic Scale Analysis of Narrow Cold Frontal Rainband During a Landfalling Atmospheric River in California During January 2021

November 20, 2023

A new paper titled “Mesoscale and Synoptic Scale Analysis of Narrow Cold Frontal Rainband During a Landfalling Atmospheric River in California During January 2021” by a group of CW3E scientists (Jerry Zou, Jay Cordeira, Sam Bartlett, Brian Kawzenuk, Shawn Roj, Chris Castellano, Chad Hecht, and Marty Ralph) was recently published in the American Geophysical Union’s Journal of Geophysical Research: Atmospheres. On 27 January 2021, an atmospheric river (AR) associated with an intense surface cyclone made landfall over coastal northern California. The landfalling AR featured both synoptic-scale and mesoscale precipitation processes related to quasi-geostrophic (QG) forcing for ascent, upslope flow, a narrow cold-frontal rainband (NCFR), potential instability and a moist absolutely unstable layer (MAUL), and likely the seeder-feeder mechanism. This particular case involved a distinctive combination of short-duration, high-impact rainfall, and moderate stratiform precipitation along the coastal regions of California, attributed to the stalling and pivoting of the NCFR. Additionally, it offers valuable insights into non-typical orographic forcing of extreme precipitation, serving as a useful addition to prior studies. This work supports the AR Research and
Applications and Modeling Capabilities for the Western United States Priority Areas in CW3E’s 2019–2024 Strategic Plan.

Our study employs high-resolution West-WRF simulations to accurately characterize the gap and core structure of the NCFR, offering reliable precipitation estimations that address the limitations of radar and satellite observations. The NCFR was supported by robust synoptic-scale QG forcing for ascent and frontogenesis. It propagated southward from Cape Mendocino to Big Sur in 12 hr before stalling and rotating counter-clockwise in central/southern California due to upstream Rossby wave breaking and an amplifying upper-tropospheric trough. With the lower to middle tropospheric flow backed considerably to the south-southwest over the NCFR, the increase of the vertical wind shear caused the transition from parallel to trailing stratiform precipitation. The stall and pivot of the AR and NCFR led to intense rainfall with a 2-day precipitation accumulation greater than 300 mm over central California. In addition, under the potential instability and frontogenesis, a MAUL between 850 and 700 hPa was captured at the leading edge of the NCFR, which indicated slantwise deep layer lifting and high precipitation efficiency.

The results of this study complement previous studies on AR-related NCFR events in California by Cannon et al. (2018, 2020) and reaffirm the importance of developing West-WRF as a cutting-edge high-resolution numerical weather prediction system with a focus on extreme precipitation and related natural hazards. High-resolution simulations offer improved insights into the physical mechanisms driving efficient air lifting, leading to intense precipitation. Furthermore, we highlight the necessity for improved observational coverage along the U.S. West Coast to capture the shallow convective structure in NCFRs, essential for monitoring and forecasting extreme precipitation events.

Figure 1: (Figure 4 from Zou et al. 2023) Parallel stratiform (PS) precipitation and trailing stratiform (TS) precipitation during the 2021 January narrow cold-frontal rain event. (a, b) 2-m temperature and 10-m wind from West-WWRF D03 (1 km) at 0600 UTC 27 January (PS) and 0000 UTC 28 January (TS), respectively. Blue arrow represents cold air advection, and white arrow represents warm air advection. (c, d) 850-hPa geopotential height (contour line), temperature (contour fill), and wind field (vector) from West-WRF D01 (9 km) at 0600 UTC 27 January and 0000 UTC 28 January, respectively. (e, f) Composite reflectivity from West-WRF D03 (1 km) at 0600 UTC 27 January and 0000 UTC 28 January, respectively. The subplot at the right corner in (c, d) are NEXRAD observations at San Francisco station (KMUX). Black boxes in (c, d) represent the domain of the subplots.

Zou, X., Cordeira, J. M., Bartlett, S. M., Kawzenuk, B., Roj, S., Castellano, C., Hecht, C., & Ralph, F. M. (2023). Mesoscale and synoptic scale analysis of narrow cold frontal rainband during a landfalling atmospheric river in California during January 2021. Journal of Geophysical Research: Atmospheres, 128(20), e2023JD039426. https://doi.org/10.1029/2023JD039426

CW3E’s Mike Dettinger reviews National Climate Assessment released November 14, 2023

CW3E’s Mike Dettinger reviews National Climate Assessment released November 14, 2023

November, 20 2023

On November 14, 2023, the Biden-Harris administration took several bold steps towards addressing the problems of human-caused climate change at national and international levels. First, it announced more than $6 billion in investments in climate action (the largest ever), with the aim of putting the US on a part towards cutting carbon emissions in half by 2023. Second, together with Chinese President Xi Jinping, Biden pledged to accelerate both nation’s efforts to address climate change and steps to reduce emissions of methane and other greenhouse gases besides CO2.

Thirdly, the administration released the Fifth National Climate Assessment on this momentous day. The Global Change Research Act of 1990 mandates that the US Global Change Research Program deliver a report to Congress and the President every 4 or 5 years that integrates, evaluates, interprets and discusses current scientific findings and uncertainties associated with global change; effects of global change on the Nation’s environment, agriculture, energy production and use, land and water resources, transportation, human health and welfare, social systems, and biological diversity; and current trends in global change, both human-induced and natural, projecting those trends for the next 25 to 100 years. The Fifth National Climate Assessment (NCA5) is the latest to fulfill that mandate. Much of NCA5 built upon the approaches, processes, and results of the Fourth National Climate Assessment (NCA4), and is the result of arduous assessments and contributions from nearly 500 authors from every State and territory, led by 14 federal agencies but including authors from many academic disciplines and all sectors. These National Climate Assessments provide scientific foundations to support informed climate-change decisions and actions across the United States, and thus are the official “word” and guidance on the topic at national level.

Such a large and comprehensive document on such an often-contentious topic requires close review and scrutiny before its release, which in this case included extensive public engagements and comments and a peer review conducted by the National Academies of Sciences, Engineering and Medicine which included extensive inputs from CW3E’s Dr. Michael Dettinger. In broadest terms, the NCA5 concludes that, even as US population and GDP have risen in the past decade, its greenhouse gas emissions have declined because the US is finally taking action. It also finds that Americans are experiencing increasing risks from extreme weather events including heavy precipitation, droughts, floods, wildfires, and heat waves, more in some settings than others. California was one such setting with atmospheric-river extremes, where CW3E has lead the science and projections of future changes. And this assessment focused more than previous ones of the fact that climate change exacerbates social inequities so that climate actions provide generally opportunities for a more resilient and just society. As chastening as such assessments are, NCA5 is an opportunity for at least some renewed optimism; we have the science, technologies and resources to address climate change, we just need the political will to do so.

Bar chart showing city- and state-level adaptation plans and actions and mitigation activities by state and territory. Notice that California is far and away the leader in adaptation activities at city and state levels, and far and away the leader in mitigation actions at the city level. Research and contributions from Scripps Institution of Oceanography, and more recently from CW3E, have helped to motivate many of these actions over the past couple of decades.