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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 rationale for effective post-fire debris flow mitigation within forested terrain

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A rationale for effective post-fire debris flow mitigation within forested terrain
Geoenvironmental Disasters, Springer | May 25, 2018...
Summary
Watersheds recently burned by wildfires are recognized as having an increased susceptibility to debris flow occurrence. The great majority occur within the first 2...
Watersheds recently burned by wildfires are recognized as having an increased susceptibility to debris flow occurrence. The great majority occur within the first 2 years following wildfires. These debris flows are generated primarily through the process of progressive entrainment of material eroded from hillslopes and channels by surface runoff and appears independent of the vegetative community burned. The decreased likelihood of debris flows over time is linked to the restoration of hydrologic function as vegetative cover and soil infiltration functioning return to pre-fire conditions. An exception to this pattern of post-wildfire debris flow susceptibility occurs in burned drainage basins with forest cover. A second, later period of increased debris flow susceptibility due to infiltration-triggered landslides can occur in burned forested basins. This later period of debris flow susceptibility is largely attributable to the fire-induced tree mortality and subsequent decay of tree root networks decreasing soil strength on steep hillslopes which produces an increased likelihood of debris flow occurrence 3 to 10 or more years after the wildfire. Consequently, post-fire mitigation measures in forested terrain must address the risk posed by debris flows caused by progressive entrainment during the 2 years following the wildfire and debris flows due to infiltration-induced debris slides three or more years later. Mitigation for the later debris flows in forested terrain involves identification of areas with infiltration-induced debris slides coincident with concentrations of fire-killed trees. Timely reforestation of these areas after a wildfire limits the loss of soil strength from decaying roots.

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A study of methods to estimate debris flow velocity

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A study of methods to estimate debris flow velocity
Landslides, Springer | September 16, 2019...
Summary
Debris flow velocities are commonly back-calculated from superelevation events which require subjective estimates of radii of curvature of bends in the debris flow...
Debris flow velocities are commonly back-calculated from superelevation events which require subjective estimates of radii of curvature of bends in the debris flow channel or predicted using flow equations that require the selection of appropriate rheological models and material property inputs. This research investigated difficulties associated with the use of these conventional velocity estimation methods. Radii of curvature estimates were found to vary with the extent of the channel investigated and with the scale of the media used, and back-calculated velocities varied among different investigated locations along a channel. Distinct populations of Bingham properties were found to exist between those measured by laboratory tests and those back-calculated from field data; thus, laboratory-obtained values would not be representative of field-scale debris flow behavior. To avoid these difficulties with conventional methods, a new preliminary velocity estimation method is presented that statistically relates flow velocity to the channel slope and the flow depth. This method presents ranges of reasonable velocity predictions based on 30 previously measured velocities.

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

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Attribution of declining western U.S. snowpack to human effects
American Meteorological Society (AMS) | December 1, 2008...
Summary
Observations show snowpack has declined across much of the western United States over the period 1950–99. This reduction has important social and economic...

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.

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California Water Plan 2013: Mountain Counties Regional Report
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California Water Plan 2013: Mountain Counties Regional Report
California Department of Water Resources (DWR) | October 30, 2014...
Summary
As the State works to solve the water crisis in California, the potential for redirected impacts in the Mountain Counties Area is acute....
As the State works to solve the water crisis in California, the potential for redirected impacts in the Mountain Counties Area is acute. It is critical that the State recognize the significance and importance of the Sierra Nevada mountain range to the local communities, the environment, the Delta, and all of California, now and for future generations.

Water resource managers are working with elected officials, governmental agencies, businesses, farmers and conservationists on innovative programs for watershed management, water use efficiency, conservation, reuse, and recycling. Water managers and others in the region are actively balancing the water supplies that support both a vibrant economy and a healthy environment. They are also continually improving the management of surface and groundwater sources to sustain this important balance for this region and California.

Statewide Significance

Water is the number one resource exported from the Sierra Nevada, and the 16-county Mountain Counties Area is the primary source for most of that exported water. The Mountain Counties Area is over 15,700 square miles and represents 9.9 percent of the state. More than 40 percent of California’s developed water supply originates in the Mountain Counties area serving end users throughout the state.

-The reservoirs in the region produce hydroelectricity to supply homes and businesses in the western United States. Mountain Counties has more hydroelectric generation facilities than any other region in California.

- Agriculture in this region feeds the state and the world and is an economic driver for California’s economy.

Recreation and tourism in the Sierra Nevada mountains help communities thrive economically as guests come from all over the world to hike, ski, fish, raft, and boat.
- Water stored behind designated reservoirs in the ten major watershed areas have dedicated in-stream flow releases designed to meet the many beneficial uses for the environment, agriculture, and urban users and provides storage to reduce the magnitude of flood flows.
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California’s Water: Protecting Headwaters
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California’s Water: Protecting Headwaters
Public Policy Institute of California (PPIC) | October 1, 2016...
Summary
Mountainous regions provide most of the state’s water supply. But major problems loom— from a growing risk of wildfires to a shrinking snowpack....

Mountainous regions provide most of the state’s water supply. But major problems loom— from a growing risk of wildfires to a shrinking snowpack. This brief outlines ways California and the federal government—the largest landowner in headwater areas—could address critical problems in these areas.

This publication is part of a briefing kit that summarizes a dozen of the state’s most pressing water management issues.

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Chinatown: Owens Valley and Western Water Reallocation—Getting the Record Straight and What It Means for Water Markets

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Chinatown: Owens Valley and Western Water Reallocation—Getting the Record Straight and What It Means for Water Markets
Texas Law Review | June 1, 2005...
Summary
In this Article I examine the notorious Owens Valley water transfer to Los Angeles. Not only was it one of the largest private...
In this Article I examine the notorious Owens Valley water transfer to Los Angeles. Not only was it one of the largest private water exchanges in U.S. history, but it remains pivotal in the political economy of western water reallocation. It involved negotiations over land and water rights between representatives of the city of Los Angeles and approximately eighteen hundred farmers and town lot owners between 1905 and 1935. By 1935, Los Angeles had acquired 95 percent of the farm acreage and 88 percent of the town properties in the valley. The water transferred from Owens Valley, a marginal agricultural area, made possible the growth of Los Angeles, and Owens Valley remains the largest single source of water for the Los Angeles Basin. Yet, the Owens Valley transfer has a very negative legacy and has hindered subsequent efforts to reallocate water from agriculture to urban and environmental uses. The negotiations for water rights and land took thirty years to complete and were often acrimonious. I analyze the negotiations between representatives of Los Angeles and Owens Valley farmers to determine the sources of bargaining conflicts. I also evaluate the economic impact of the exchange on both parties to show that each party was made substantially better off. Yet, the notion of “theft” remains. To explain this, I examine the distribution of the economic benefits of the water and land sale. Distributional issues take on greater importance when there are valuation disputes and the gains from trade are shared very unequally. With these insights, I conclude with lessons for contemporary western water reallocation.

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Climate and landscape drive the pace and pattern of conifer encroachment into subalpine meadows

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Climate and landscape drive the pace and pattern of conifer encroachment into subalpine meadows
Ecological Applications, Ecological Society of America | May 8, 2018...
Summary
Mountain meadows have high biodiversity and help regulate stream water release following the snowmelt pulse. However, many meadows are experiencing woody plant encroachment,...

Mountain meadows have high biodiversity and help regulate stream water release following the snowmelt pulse. However, many meadows are experiencing woody plant encroachment, threatening these ecosystem services. While there have been field surveys of individual meadows and remote sensing‐based landscape‐scale studies of encroachment, what is missing is a broad‐scale, ground‐based study to understand common regional drivers, especially at high elevations, where land management has often played a less direct role. With this study, we ask: What are the climate and landscape conditions conducive to woody plant encroachment at the landscape scale, and how has historical climate variation affected tree recruitment in subalpine meadows over time? We measured density of encroaching trees across 340 subalpine meadows in the central Sierra Nevada, California, USA, and used generalized additive models (GAMs) to determine the relationship between landscape‐scale patterns of encroachment and meadow environmental properties. We determined ages of trees in 30 survey meadows, used observed climate and GAMs to model the relationship between timing of recruitment and climate since the early 1900s, and extrapolated recruitment patterns into the future using downscaled climate scenarios. Encroachment was high among meadows with lodgepole pine (Pinus contorta Douglas ex Loudon var. murrayana (Balf.) Engelm.) in the immediate vicinity, at lower elevations, with physical conditions favoring strong soil drying, and with maximum temperatures above or below average. Climatic conditions during the year of germination were unimportant, with tree recruitment instead depending on a 3‐yr seed production period prior to germination and a 6‐yr seedling establishment period following germination. Recruitment was high when the seed production period had high snowpack, and when the seedling establishment period had warm summer maximum temperatures, high summer precipitation, and high snowpack. Applying our temporal model to downscaled output from four global climate models indicated that the average meadow will shift to forest by the end of the 21st century. Sierra Nevada meadow encroachment by conifers is ubiquitous and associated with climate conditions increasingly favorable for tree recruitment, which will lead to substantial changes in subalpine meadows and the ecosystem services they provide.

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Climate change is increasing the risk of extreme autumn wildfire conditions across California

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Climate change is increasing the risk of extreme autumn wildfire conditions across California
Environmental Research Letters, IOP Publishing | March 26, 2020...
Summary
California has experienced devastating autumn wildfires in recent years. These autumn wildfires have coincided with extreme fire weather conditions during periods of strong offshore...
California has experienced devastating autumn wildfires in recent years. These autumn wildfires have coincided with extreme fire weather conditions during periods of strong offshore winds coincident with unusually dry vegetation enabled by anomalously warm conditions and late onset of autumn precipitation. In this study, we quantify observed changes in the occurrence and magnitude of meteorological factors that enable extreme autumn wildfires in California, and use climate model simulations to ascertain whether these changes are attributable to human-caused climate change. We show that state-wide increases in autumn temperature (~1 °C) and decreases 39 in autumn precipitation (~30%) over the past four decades have contributed to increases in aggregate fire weather indices (+20%). As a result, the observed frequency of autumn days with extreme (95th percentile) fire weather – which we show are preferentially associated with extreme autumn wildfires – has more than doubled in California since the early 1980s. We further find an increase in the climate model-estimated probability of these extreme autumn conditions since ~1950, including a long-term trend toward increased same-season co-occurrence of extreme fire weather conditions in northern and southern California. Our climate model analyses suggest that continued climate change will further amplify the number of days with extreme fire weather by the end of this century, though a pathway consistent with the UN Paris commitments would substantially curb that increase. Given the acute societal impacts of extreme autumn wildfires in recent years, our findings have critical relevance for ongoing efforts to manage wildfire risks in California and other regions.

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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 rationale for effective post-fire debris flow mitigation within forested terrain

A rationale for effective post-fire debris flow mitigation within forested terrain

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A study of methods to estimate debris flow velocity

A study of methods to estimate debris flow velocity

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

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

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California Water Plan 2013: Mountain Counties Regional Report

California Water Plan 2013: Mountain Counties Regional Report

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California’s Water: Protecting Headwaters

California’s Water: Protecting Headwaters

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Chinatown: Owens Valley and Western Water Reallocation—Getting the Record Straight and What It Means for Water Markets

Chinatown: Owens Valley and Western Water Reallocation—Getting the Record Straight and What It Means for Water Markets

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Climate and landscape drive the pace and pattern of conifer encroachment into subalpine meadows

Climate and landscape drive the pace and pattern of conifer encroachment into subalpine meadows

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Climate change is increasing the risk of extreme autumn wildfire conditions across California

Climate change is increasing the risk of extreme autumn wildfire conditions across California

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