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21st century California drought risk linked to model fidelity of the El Niño teleconnection

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21st century California drought risk linked to model fidelity of the El Niño teleconnection
Nature Climate and Atmospheric Science | September 3, 2018...
Summary
Greenhouse gas-induced climate change is expected to lead to negative hydrological impacts for southwestern North America, including California (CA). This includes a decrease...
Greenhouse gas-induced climate change is expected to lead to negative hydrological impacts for southwestern North America, including California (CA). This includes a decrease in the amount and frequency of precipitation, reductions in Sierra snow pack, and an increase in evapotranspiration, all of which imply a decline in surface water availability, and an increase in drought and stress on water resources. However, a recent study showed the importance of tropical Pacific sea surface temperature (SST) warming and an El Niño Southern Oscillation (ENSO)-like teleconnection in driving an increase in CA precipitation through the 21st century, particularly during winter (DJF). Here, we extend this prior work and show wetter (drier) CA conditions, based on several drought metrics, are associated with an El Niño (La Niña)-like SST pattern. Models that better simulate the observed ENSO-CA precipitation teleconnection also better simulate the ENSO-CA drought relationships, and yield negligible change in the risk of 21st century CA drought, primarily due to wetting during winter. Seasonally, however, CA drought risk is projected to increase during the non-winter months, particularly in the models that poorly simulate the observed teleconnection. Thus, future projections of CA drought are dependent on model fidelity of the El Niño teleconnection. As opposed to focusing on adapting to less water, models that better simulate the teleconnection imply adaptation measures focused on smoothing seasonal differences for affected agricultural, terrestrial, and aquatic systems, as well as effectively capturing enhanced winter runoff.

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A Measure of Snow: A Report Based on Case Studies of The Snow Survey and Water Supply Forecasting Program

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A Measure of Snow: A Report Based on Case Studies of The Snow Survey and Water Supply Forecasting Program
U.S. Department of Agriculture (USDA), Natural Resources Conservation Service | November 1, 2008...
Summary
Snow depth and snow water content data have been collected and disseminated throughout the Western United States for over 100 years. Early snow survey and...

Snow depth and snow water content data have been collected and disseminated throughout the Western United States for over 100 years. Early snow survey and water supply data were gathered through the efforts of university scientists, beginning with the work of Dr. James E. Church. In 1935, the Soil Conservation Service (SCS), now the United States Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS), established a formal cooperative Snow Survey and Water Supply Forecasting (SS-WSF) Program. The Agency was charged with responsibility for “conducting snow survey and water supply forecasts and the forecasting of irrigation water supplies.” The new Program would also develop consistent methods for measuring snow and reliable models for accurate water supply forecasting.

Administered by NRCS, the SS-WSF Program has grown into a network of more than 1,200 manually-measured snow courses and over 750 automated Snowpack Telemetry (SNOTEL) weather stations in 13 Western States, including Alaska. (See map on page 4.) The SS-WSF Program provides manual snow course data collected by NRCS conservation professionals, automated SNOTEL data, and modeled water supply/streamflow volume data as well as issues streamflow forecasts for over 740 locations in the West. The data and the related reports and forecasts, are made available—in near real time for the automated SNOTEL sites—to private industry; to Federal, State, and local government entities; and to private citizens through an extensive Internet delivery system and other distribution channels.

With 50-80 percent of the water supply in the West arriving in the form of snow, data on the snowpack provides critical information to decision-makers and water managers throughout the West. The basic data become even more valuable when used in concert with partner organizations to provide water supply forecasting tailored to meet end-user needs. According to researchers from multiple U.S. and international agencies, research centers, and academia, changes in the world’s climate have resulted in a loss of predictability in weather, precipitation, and water transport and accumulation patterns. It is anticipated that the value the SS-WSF Program provides to society will increase over time as climate variability increases.

Recently a study was done to see who uses SS-WSF data, how the data are used, and the value of the data. Users of the data were interviewed and specific events and activities were analyzed. This publication is based on that study.

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A Measure of Snow: Case Studies of the Snow Survey and Water Supply Forecasting Program

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A Measure of Snow: Case Studies of the Snow Survey and Water Supply Forecasting Program
U.S. Department of Agriculture (USDA), Natural Resources Conservation Service | September 1, 2010...
Summary
Snow depth and snow water content data have been collected and disseminated throughout the W estern United States for over 100 years. Early...

Snow depth and snow water content data have been collected and disseminated throughout the W estern United States for over 100 years. Early Snow Survey and Water Supply Forecasting data were gathered through the efforts of university scientists. In 1935, the Soil Conservation Service (SCS) was given $36,000 to establish a formal cooperative Snow Survey and Water Supply Forecasting (SSWSF) Program. The agency was charged with the responsibility for “conducting Snow Survey and Water Supply Forecast s and forecasting of irrigation water supplies.” The new program would also develop consistent methods for measuring snow and reliable models for water supply forecasting.

Using a case study approach, this report assesses the various uses of data gathered and published by the SSWSF Program and estimates the value of those data in terms of both the market and non-market values of the information. Additionally, it evaluate s the relative merits of maintaining the program as a publicly funded program as opposed to privatizing the program.

This study finds that the SSWSF Program is generating both market and non-market benefits to the U.S. economy and to U.S. society as a whole that are worth significantly more than the cost of the program. Should climate variability increase — as is expected by many of those interviewed in the course of completing this study, and as current climate research strongly suggests — the value of the information provided by the SSWSF Program will increase accordingly.

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A spatially comprehensive, hydrometeorological data set for Mexico, the U.S., and Southern Canada 1950–2013

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A spatially comprehensive, hydrometeorological data set for Mexico, the U.S., and Southern Canada 1950–2013
Nature | August 18, 2015...
Summary
A data set of observed daily precipitation, maximum and minimum temperature, gridded to a 1/16° (~6 km) resolution, is described that spans the...

A data set of observed daily precipitation, maximum and minimum temperature, gridded to a 1/16° (~6 km) resolution, is described that spans the entire country of Mexico, the conterminous U.S. (CONUS), and regions of Canada south of 53° N for the period 1950–2013. The dataset improves previous products in spatial extent, orographic precipitation adjustment over Mexico and parts of Canada, and reduction of transboundary discontinuities. The impacts of adjusting gridded precipitation for orographic effects are quantified by scaling precipitation to an elevation-aware 1981–2010 precipitation climatology in Mexico and Canada. Differences are evaluated in terms of total precipitation as well as by hydrologic quantities simulated with a land surface model. Overall, orographic correction impacts total precipitation by up to 50% in mountainous regions outside CONUS. Hydrologic fluxes show sensitivities of similar magnitude, with discharge more sensitive than evapotranspiration and soil moisture. Because of the consistent gridding methodology, the current product reduces transboundary discontinuities as compared with a commonly used reanalysis product, making it suitable for estimating large-scale hydrometeorologic phenomena.

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A tale of two California droughts: Lessons amidst record warmth and dryness in a region of complex physical and human geography

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A tale of two California droughts: Lessons amidst record warmth and dryness in a region of complex physical and human geography
American Geophysical Union (AGU) | November 19, 2015...
Summary
The state of California has experienced the worst drought in its historical record during 2012–2015. Adverse effects of this multi year event have been...
The state of California has experienced the worst drought in its historical record during 2012–2015. Adverse effects of this multi year event have been far from uniformly distributed across the region, ranging from remarkably mild in most of California’s densely populated coastal cities to very severe in more rural, agricultural, and wildfire-prone regions. This duality of impacts has created a tale of two very different California droughts—highlighting enhanced susceptibility to climate stresses at the environmental andsocioeconomic margins of California. From a geophysical perspective, the persistence of related atmospheric anomalies has raised a number of questions regarding the drought’s origins—including the role of anthropogenic climate change. Recent investigations underscore the importance of understanding the underlying physical causes of extremes in the climate system, and the present California drought represents an excellent case study for such endeavors. Meanwhile, a powerful El Niño event in the Pacific Ocean offers the simultaneous prospect of partial drought relief but also an increased risk of flooding during the 2015–2016 winter—a situation illustrative of the complex hydroclimatic risks California and other regions are likely to face in a warming world.

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A Twenty-First-Century California Observing Network for Monitoring Extreme Weather Events

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A Twenty-First-Century California Observing Network for Monitoring Extreme Weather Events
Journal of Atmospheric and Oceanic Technology, American Meteorological Society | August 27, 2013...
Summary
During Northern Hemisphere winters, the West Coast of North America is battered by extratropical storms. The impact of these storms is of paramount...
During Northern Hemisphere winters, the West Coast of North America is battered by extratropical storms. The impact of these storms is of paramount concern to California, where aging water supply and flood protection infrastructures are challenged by increased standards for urban flood protection, an unusually variable weather regime, and projections of climate change. Additionally, there are inherent conflicts between releasing water to provide flood protection and storing water to meet requirements for the water supply, water quality, hydropower generation, water temperature and flow for at-risk species, and recreation. To improve reservoir management and meet the increasing demands on water, improved forecasts of precipitation, especially during extreme events, are required. Here, the authors describe how California is addressing their most important and costliest environmental issue-water management-in part, by installing a state-of-the-art observing system to better track the area's most severe wintertime storms.

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An Assessment of Urban Water Demand Forecasts in California

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An Assessment of Urban Water Demand Forecasts in California
Pacific Institute | August 5, 2020...
Summary
In California, urban per capita water demand has declined dramatically over the past several decades, driven in part by greater uptake of water-efficient...
In California, urban per capita water demand has declined dramatically over the past several decades, driven in part by greater uptake of water-efficient devices. These reductions have important implications for estimating future water demand. However, failure to account for the long-term trend of declining per capita water demand has led to routine overestimation of future water demand. This can lead to unnecessary and costly investment in unneeded infrastructure and new sources of supply, higher costs, and adverse environmental impacts.

This report examines the accuracy of long-range water demand forecasts for California’s 10 largest urban water suppliers. It finds that per capita water demand declined for all water suppliers between 2000 and 2015. In most cases, reductions in per capita water demand were so large that total water demand declined during this period. Additionally, all water suppliers overestimated demand, driven largely by inflated estimates of per capita water demand and, to a lesser extent, overestimates of population growth rates. The report offers recommendations on how to improve the accuracy of long-range water demand forecasts.

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An evaluation of atmospheric rivers over the North Pacific in CMIP5 and their response to warming under RCP 8.5

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An evaluation of atmospheric rivers over the North Pacific in CMIP5 and their response to warming under RCP 8.5
American Geophysical Union (AGU) | November 13, 2015...
Summary
Landfalling atmospheric rivers over the North Pacific are evaluated in historical (1980–2005) simulations from 28 models participating in the fifth phase of the Coupled...
Landfalling atmospheric rivers over the North Pacific are evaluated in historical (1980–2005) simulations from 28 models participating in the fifth phase of the Coupled Model Intercomparison Project (CMIP5) and compared to the Modern-Era Retrospective Analysis for Research and Applications and ERA-Interim reanalyses. Landfalling dates are identified as having spatially elongated high wind and moisture features in physical proximity to the coastline. Model performance relative to reanalysis is found to be quite variable. The majority can resolve the spatial structure of landfalling events, but few correctly resolve the frequency distribution, interannual variability in number and amplitude of moisture flux, and median landfalling latitude. The response of a subset of high-performing models to projected warming at the end of the 21st century is investigated using Representative Concentration Pathway (RCP) 8.5 (2070–2100) projections. Selected models show a broadening of the frequency distribution, with the largest increase in frequency occurring equatorward of peak historical frequency. While there is a robust increase in AR-related moisture transport compared to the historical period, this increase is not linked to more extreme AR events within the context of the projected future climate. The occurrence of years with many AR dates is greater at the end of the 21st century than during the historical period. The equatorward increase in peak historical frequency is colocated with increases in the 850 and 250 hPa zonal winds. The response in moisture flux to warming is mostly thermodynamic, but equatorward of its peak distribution, it is dominated by a dynamic response.

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Anthropogenic warming impacts on California snowpack during drought

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Anthropogenic warming impacts on California snowpack during drought
American Geophysical Union (AGU) | March 15, 2017...
Summary
Sierra Nevada climate and snowpack is simulated during the period of extreme drought from 2011 to 2015 and compared to an identical simulation...
Sierra Nevada climate and snowpack is simulated during the period of extreme drought from 2011 to 2015 and compared to an identical simulation except for the removal of the twentieth century anthropogenic warming. Anthropogenic warming reduced average snowpack levels by 25%, with middle‐to‐low elevations experiencing reductions between 26 and 43%. In terms of event frequency, return periods associated with anomalies in 4 year 1 April snow water equivalent are estimated to have doubled, and possibly quadrupled, due to past warming. We also estimate effects of future anthropogenic warmth on snowpack during a drought similar to that of 2011–2015. Further snowpack declines of 60–85% are expected, depending on emissions scenario. The return periods associated with future snowpack levels are estimated to range from millennia to much longer. Therefore, past human emissions of greenhouse gases are already negatively impacting statewide water resources during drought, and much more severe impacts are likely to be inevitable.

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Anthropogenic Warming Impacts on Today’s Sierra Nevada Snowpack and Flood Risk

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Anthropogenic Warming Impacts on Today’s Sierra Nevada Snowpack and Flood Risk
American Geophysical Union (AGU) | June 15, 2018...
Summary
This study investigates temperature impacts to snowpack and runoff‐driven flood risk over the Sierra Nevada during the extremely wet year of 2016–2017, which...
This study investigates temperature impacts to snowpack and runoff‐driven flood risk over the Sierra Nevada during the extremely wet year of 2016–2017, which followed the extraordinary California drought of 2011–2015. By perturbing near‐surface temperatures from a 9‐km dynamically downscaled simulation, a series of offline land surface model experiments explore how Sierra Nevada hydrology has already been impacted by historical anthropogenic warming and how these impacts evolve under future warming scenarios. Results show that historical warming reduced 2016–2017 Sierra Nevada snow water equivalent by 20% while increasing early‐season runoff by 30%. An additional one third to two thirds loss of snowpack is projected by the end of the century, depending on the emission scenario, with middle elevations experiencing the most significant declines. Notably, the number of days in the future with runoff exceeding 20 mm nearly doubles under a mitigation emission scenarios and triples under a business‐as‐usual scenario. A smaller snow‐to‐rain ratio, as opposed to increased snowmelt, is found to be the primary mechanism of temperature impacts to Sierra snowpack and runoff. These findings are consequential to the prevalence of early‐season floods in the Sierra Nevada. In the Feather River Watershed, historical warming increased runoff by over one third during the period of heaviest precipitation in February 2017. This suggests that historical anthropogenic warming may have exacerbated runoff conditions underlying the Oroville Dam spillway overflow that occurred in this month. As warming continues in the future, the potential for runoff‐based flood risk may rise even higher.

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21st century California drought risk linked to model fidelity of the El Niño teleconnection

21st century California drought risk linked to model fidelity of the El Niño teleconnection

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A Measure of Snow: A Report Based on Case Studies of The Snow Survey and Water Supply Forecasting Program

A Measure of Snow: A Report Based on Case Studies of The Snow Survey and Water Supply Forecasting Program

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A Measure of Snow: Case Studies of the Snow Survey and Water Supply Forecasting Program

A Measure of Snow: Case Studies of the Snow Survey and Water Supply Forecasting Program

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A spatially comprehensive, hydrometeorological data set for Mexico, the U.S., and Southern Canada 1950–2013

A spatially comprehensive, hydrometeorological data set for Mexico, the U.S., and Southern Canada 1950–2013

Become a member to access this feature

A tale of two California droughts: Lessons amidst record warmth and dryness in a region of complex physical and human geography

A tale of two California droughts: Lessons amidst record warmth and dryness in a region of complex physical and human geography

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A Twenty-First-Century California Observing Network for Monitoring Extreme Weather Events

A Twenty-First-Century California Observing Network for Monitoring Extreme Weather Events

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An Assessment of Urban Water Demand Forecasts in California

An Assessment of Urban Water Demand Forecasts in California

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An evaluation of atmospheric rivers over the North Pacific in CMIP5 and their response to warming under RCP 8.5

An evaluation of atmospheric rivers over the North Pacific in CMIP5 and their response to warming under RCP 8.5

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Anthropogenic warming impacts on California snowpack during drought

Anthropogenic warming impacts on California snowpack during drought

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Anthropogenic Warming Impacts on Today’s Sierra Nevada Snowpack and Flood Risk

Anthropogenic Warming Impacts on Today’s Sierra Nevada Snowpack and Flood Risk

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