The 2010/2011 snow season in California’s Sierra Nevada: Role of atmospheric rivers and modes of large-scale variability

American Geophysical Union (AGU) | October 17th, 2013

The anomalously snowy winter season of 2010/2011 in the Sierra Nevada is analyzed interms of snow water equivalent (SWE) anomalies and the role of atmospheric rivers (AR

The anomalously snowy winter season of 2010/2011 in the Sierra Nevada is analyzed interms of snow water equivalent (SWE) anomalies and the role of atmospheric rivers (ARs)—narrow channels of enhanced meridional water vapor transport between the tropics and extratropics. Mean April 1 SWE was 0.44 m (56%) above normal averaged over 100 snow sensors. AR occurrence was anomalously high during the period, with 20 AR dates during the season and 14 in the month of December 2010, compared to the mean occurrence of nine dates per season. Fifteen out of the 20 AR dates were associated with the negative phases of the Arctic Oscillation (AO) and the Pacific-North American (PNA) teleconnection pattern. Analysis of all winter ARs in California during water years 1998–2011 indicates more ARs occur during the negative phase of AO and PNA, with the increase between positive and negative phases being90% for AO, and50% for PNA. The circulation pattern associated with concurrent negative phases of AO and PNA, characterized by cyclonic anomalies centered northwest of California, provides a favorable dynamical condition for ARs. The analysis suggests that the massive Sierra Nevada snowpack during the 2010/2011 winter season is primarily related to anomalously high frequency of ARs favored by the joint phasing of AO and PNA, and that a secondary contribution is from increased snow accumulation during these ARs favored by colder air temperatures associated with AO, PNA, and La Nina.

The 2025-26 Budget: Proposition 4 Spending Plan

Legislative Analyst's Office (LAO) | February 12th, 2025

The approaching obsolescence of 137Cs dating of wetland soils in North America

Quaternary Science Reviews (Elsevier) | September 24th, 2018

The peak fallout in 1963 of the radionuclide 137Cs has been used to date lake, reservoir, continental shelf, and wetland sedimentary deposits. In wetlands such dating is

The peak fallout in 1963 of the radionuclide 137Cs has been used to date lake, reservoir, continental shelf, and wetland sedimentary deposits. In wetlands such dating is used to project the ability of wetlands to keep pace with sea level rise and develop strategies for mitigating carbon pollution using biological carbon sequestration. Here we demonstrate that reliable 137Cs profiles are increasingly difficult to obtain from wetland soils. Among 58 soil cores recently collected from a range of wetland types and 137Cs fallout densities across the United States, 25% contain no identifiable 137Cs peaks. Less than 40% of 137Cs ages are consistent with 210Pb dating. We provide a new measure of 137Cs peak clarity (t) for our core dataset by comparing the 50% interquartile range of data around the 137Cs peak for “ideal” cores profiles determined using 137Cs fallout data to that of observed core profiles. Our results show that overall t is approximately 10 times greater for observed cores than ideal cores. The deterioration in the 137Cs peak has occurred due to radionuclide decay, 137Cs migration in situ, which is ubiquitous in this study, and 137Cs amendments from surface waters. Such deterioration likely extends to both Mexican and non-permafrost, Canadian wetlands. We recommend continued use of 137Cs only if the full bound of dating uncertainty for both 137Cs and an additional method such as 210Pb is propagated into estimates of wetland vertical accretion and carbon sequestration.

The Big Water Supply Shift: Groundwater Key to Water Security in California's Changing Climate

Union of Concerned Scientists | November 1st, 2015

For more than a century, California has relied on its snowmelt-fed reservoirs, rivers, and streams for the majority of its water, but drought and climate chang

For more than a century, California has relied on its snowmelt-fed reservoirs, rivers, and streams for the majority of its water, but drought and climate change are depleting those traditional supplies. Snow is already melting as many as 30 days earlier than in the mid-twentieth century, meaning less water is available during the hotter months when water demand is highest. California is increasingly turning to groundwater to meet its water needs. Today, groundwater supplies up to 50 percent of California’s water, but California’s prolonged drought has led to the over-pumping of groundwater, overdrafting the Central Valley’s aquifers. Sustainable groundwater management will allow the state to adapt to climate change while increasing water reliability in the future.

The case for strategic and managed climate retreat

American Association for the Advancement of Science (AAAS) | August 23rd, 2019

Faced with global warming, rising sea levels, and the climate-related extremes they intensify, the question is no longer whether some communities will retreat�

Faced with global warming, rising sea levels, and the climate-related extremes they intensify, the question is no longer whether some communities will retreat—moving people and assets out of harm’s way—but why, where, when, and how they will retreat. To the extent that retreat is already happening, it is typically ad hoc and focused on risk reduction in isolation from broader societal goals. It is also frequently inequitable and often ignores the communities left behind or those receiving people who retreat. Retreat has been seen largely as a last resort, a failure to adapt, or a one-time emergency action; thus, little research has focused on retreat, leaving practitioners with little guidance. Such a narrow conception of retreat has limited decision-makers’ perception of the tools available and stilted innovation. We propose a reconceptualization of retreat as a suite of adaptation options that are both strategic and managed. Strategy integrates retreat into long-term development goals and identifies why retreat should occur and, in doing so, influences where and when. Management addresses how retreat is executed. By reconceptualizing retreat as a set of tools used to achieve societal goals, communities and nations gain additional adaptation options and a better chance of choosing the actions most likely to help their communities thrive.

The Case of Shifting Snow

Climate Central | February 5th, 2020

Whether you live among palm trees or pine trees, snow plays a critical role in our climate. Snow keeps our planet cooler, significantly affects water resources, and is a

Whether you live among palm trees or pine trees, snow plays a critical role in our climate. Snow keeps our planet cooler, significantly affects water resources, and is a revealing indicator of climate change. Forecasting snowfall and determining long-term trends of snow climatology are inherently challenging, but the research team at Climate Central has produced an analysis of snowfall trends across the United States. While no single overall national trend in snowfall can be discerned from the results, clear regional and seasonal patterns do emerge. In almost all areas of the country, snow is decreasing in the “shoulder” seasons—fall and spring. Results from 145 locations show that 116 stations (80%) had decreased snowfall before December, and 96 stations (66%) had decreased snowfall after March 1. Winter showed a mixed record, with more snow in northern climates, and decreasing snow in the southern regions. We also compared total snowfall from the 1970s to the 2010s and ranked the 20 cities with the biggest percentage gains and losses, using endpoint analysis. The changing patterns of how much, when, and where snow falls have significant impacts on our climate, our economy, and our lives. This report provides a primer on the climatology of snow and includes resources on how to report on snow—or the lack of it—in your area.

The challenge of closing the climate adaptation gap for water supply utilities

Nature Portfolio (Springer Nature) | June 29th, 2024

The challenge of hot drought

Nature Portfolio (Springer Nature) | November 21st, 2013

Drought is heating up around the warming world. Particularly hot drought has cost more than US$40 billion and claimed 218 human lives since 2010 in the United States alon

Drought is heating up around the warming world. Particularly hot drought has cost more than US$40 billion and claimed 218 human lives since 2010 in the United States alone. These hot and dry conditions have also contributed to unusually widespread and devastating wildfires, fuelled by wide expanses of weakened and dead trees that were unable to deal with heat stress and subsequent insect attack. Yet, to get a real sense of how this recent change in drought severity might shape the future, one has to look to the past. An analysis of regional and pan-continental North American drought over the past 1,000 years, reported by Cook et al in the Journal of Climate, makes it clear that recent droughts, as costly as they have been, are only a taste of what might lie ahead, independently of any big climate change.

The challenge of unprecedented floods and droughts in risk management

Nature Portfolio (Springer Nature) | August 3rd, 2022

Risk management has reduced vulnerability to floods and droughts globally, yet their impacts are still increasing. An improved understanding of the causes of changing imp

Risk management has reduced vulnerability to floods and droughts globally, yet their impacts are still increasing. An improved understanding of the causes of changing impacts is therefore needed, but has been hampered by a lack of empirical data. On the basis of a global dataset of 45 pairs of events that occurred within the same area, we show that risk management generally reduces the impacts of floods and droughts but faces difficulties in reducing the impacts of unprecedented events of a magnitude not previously experienced. If the second event was much more hazardous than the first, its impact was almost always higher. This is because management was not designed to deal with such extreme events: for example, they exceeded the design levels of levees and reservoirs. In two success stories, the impact of the second, more hazardous, event was lower, as a result of improved risk management governance and high investment in integrated management. The observed difficulty of managing unprecedented events is alarming, given that more extreme hydrological events are projected owing to climate change.

The Changing Nature of Atmospheric Rivers

American Meteorological Society (AMS) | March 15th, 2025

Atmospheric rivers (ARs) are expected to strengthen in a warming climate, largely due to the thermodynamic (moistening) effect. Here, we show that this trend is already e

Atmospheric rivers (ARs) are expected to strengthen in a warming climate, largely due to the thermodynamic (moistening) effect. Here, we show that this trend is already evident in historical reanalysis data using the AR Tracking Method Intercomparison Project (ARTMIP) tier 2 AR detection tools (ARDTs) and variants of our own global AR detection applied to ERA5, MERRA-2, and JRA-55 reanalysis data. Over the 1980–2019 (ARTMIP) and 1980–2023 (variants) periods, total AR area increased by 6%–9%. AR integrated water vapor (IWV) increased by 1.5%–2.5% while integrated vapor transport (IVT) increased by less than 1% and 850-hPa wind speed (|V850|) and vertically integrated moisture flux convergence (VIMFC) both decreased. IWV increases were the most robust overall. All trend magnitudes were sensitive to subsetting, with fixed-frequency subsets consisting of the most intense AR grid points showing larger increases of 3%–4% IVT, 4%–6% IWV, and 6%–10% VIMFC, this last opposing a decreasing AR-mean VIMFC trend likely associated with large area increases. For individual ARs, maximum IVT and IWV increased at ;3–63 and ;1.5–23 the rate of AR-mean values, respectively. Regional changes were often even larger, particularly for extreme events, though most geospatial trends had low detectability under a false discovery rate control framework. Ultimately, despite considerable ARDT and methodological diversity, we found robust consensus moistening and expansion of ARs between 1980 and 2023. However, further research is required to determine the extent to which these trends are affected by reanalysis observational assimilation changes. For example, previous studies indicate that certain reanalyses misrepresent 1980–94 atmospheric moistening and so may underestimate historical AR expansion and intensification rates.