NW Climate Science Digest

Aquatic Resources, Stream Flow, Hydrology in the Western U.S.

Trends in snow cover and other variables at weather stations in the conterminous US

Knowles, N. (2015). Trends in Snow Cover and Related Quantities at Weather Stations in the Conterminous United States. Journal of Climate28(19), 7518-7528.

Noah Knowles from the USGS used three statistical analyses (trend tests, linear regression, and canonical correlation analysis) to study National Weather Service Cooperative Observer (COOP) changes to snow depth data from 1950-2010. Knowles showed that patterns toward later snow-cover onset in the western half of the conterminous United States and earlier snow-cover onset in the eastern half, combined with a widespread trend toward earlier final meltoff of snow cover produced shorter snow seasons in the eastern half of the United States and longer snow seasons in the Great Plains and southern Rockies. Additionally, the annual total number of days with snow cover exhibited a widespread decline. Knowles concluded that temperature is the dominant variable influencing snow cover during the warmer snow-season months, while the colder months are dominated by a combination of temperature and precipitation. A canonical correlation analysis indicated that most trends presented here took hold in the 1970s, consistent with the temporal pattern of global warming during the study period.

Improved bias correction techniques for hydrologic simulations of climate change

Pierce, D. W., Cayan, D. R., Maurer, E. P., Abatzoglou, J. T., & Hegewisch, K. C. (2015). Improved bias correction techniques for hydrological simulations of climate change. Journal of Hydrometeorology, (2015).

Global climate model output typically needs to be bias corrected before it can be used for climate change impact studies. Researchers from Scripps, USGS, Santa Clara and University of Idaho applied three existing bias correction methods, and one new one they developed, to daily maximum temperature and precipitation from 21 global climate models (GCMs) to investigate how different methods alter the climate change signal of the GCM. The quantile mapping (QM) and cumulative distribution function transform (CDF-t) bias correction methods significantly altered the GCM’s mean climate change signal, with differences of up to 2°C and 30 percentage points for monthly mean temperature and precipitation, respectively. Equidistant quantile matching (EDCDFm) bias correction preserved GCM changes in mean daily maximum temperature, but not precipitation. An extension to EDCDFm termed PresRat was introduced, which generally preserved the GCM changes in mean precipitation. Another problem is that GCMs can have difficulty simulating variance as a function of frequency. To address this, a frequency-dependent bias correction method was introduced that is twice as effective as standard bias correction in reducing errors in the models’ simulation of variance as a function of frequency, and does so without making any locations worse, unlike standard bias correction. Lastly, a preconditioning technique was introduced that improved the simulation of the annual cycle while still allowing the bias correction to take account of an entire season’s values at once.

Patterns of precipitation change and climatological uncertainty

Langenbrunner, B., Neelin, J. D., Lintner, B. R., & Anderson, B. T. (2015). Patterns of precipitation change and climatological uncertainty among CMIP5 models, with a focus on the midlatitude Pacific storm track. Journal of Climate, (2015).

Projections of changes in precipitation from global warming scenarios display disagreement at regional scales. Scientists from UCLA, the State University of New Jersey, and Boston University examined spatial patterns of disagreement in the simulated climatology and end-of-century precipitation changes in phase 5 of the Coupled Model Intercomparison Project (CMIP5) archive. The term principal uncertainty pattern (PUP) was used for any robust mode calculated when applying these techniques to a multimodel ensemble. This study found two PUPs in the tropics, one at the margins of the convection zones and the other in the Pacific cold tongue. Both modes appear to arise primarily from differences in the response to radiative forcing, distinct from internal variability. The leading storm-track PUPs for precipitation and zonal wind change exhibited similarities to the leading uncertainty patterns for the historical climatology, which indicated important and parallel sensitivities in the eastern Pacific storm-track. However, expansion coefficients for climatological uncertainties tended to be weakly correlated with those for end-of-century change

Projected changes in snowfall extremes and interannual variability of snowfall in the western United States

Lute, A. C., J. T. Abatzoglou, and K. C. Hegewisch (2015), Projected changes in snowfall extremes and interannual variability of snowfall in the western United States, Water Resour. Res., 51, 960–972, doi:10.1002/2014WR016267.

Projected warming will have significant impacts on snowfall accumulation and melt, with implications for water availability and management in snow-dominated regions. Changes in snowfall extremes are confounded by projected increases in precipitation extremes. Three scientists from the University of Idaho bias-corrected downscaled climate projections from 20 global climate models to montane Snowpack Telemetry stations across the western United States. The study assessed mid-21st century changes in the mean and the variability of annual snowfall water equivalent (SFE) and extreme snowfall events. The researchers found that changes in the magnitude of snowfall event quantiles were sensitive to historical winter temperature. At climatologically cooler locations, such as in the Rocky Mountains, changes in the magnitude of snowfall events mirrored changes in the distribution of precipitation events, with increases in extremes and less change in more moderate events. By contrast, declines in snowfall event magnitudes were found for all quantiles in warmer locations. Common to both warmer and colder sites was a relative increase in the magnitude of snowfall extremes compared to annual SFE and a larger fraction of annual SFE from snowfall extremes. The coefficient of variation of annual SFE increased up to 80% in warmer montane regions due to projected declines in snowfall days and the increased contribution of snowfall extremes to annual SFE. In addition to declines in mean annual SFE, more frequent low-snowfall years and less frequent high-snowfall years were projected for every station.

Local variability mediates vulnerability of trout populations to land use and climate change

Penaluna, B. E., Dunham, J. B., Railsback, S. F., Arismendi, I., Johnson, S. L., Bilby, R. E., ... & Skaugset, A. E. (2015). Local variability mediates vulnerability of trout populations to land use and climate change. PloS one10(8), e0135334.

Land use and climate change occur simultaneously around the globe. Fully understanding their separate and combined effects requires a mechanistic understanding at the local scale where their effects are ultimately realized. In this study, a group of researchers applied an individual-based model of fish population dynamics to evaluate the role of local stream variability in modifying responses of Coastal Cutthroat Trout (Oncorhynchus clarkii clarkii) to scenarios simulating identical changes in temperature and stream flows linked to forest harvest, climate change, and their combined effects over six decades. The study found that climate change most strongly influenced trout (earlier fry emergence, reductions in biomass of older trout, increased biomass of young-of-year), but these changes did not consistently translate into reductions in biomass over time. Forest harvest, in contrast, produced fewer and less consistent responses in trout. Earlier fry emergence driven by climate change was the most consistent simulated response, whereas survival, growth, and biomass were inconsistent. Overall the findings from this study indicate that a host of local processes can strongly influence how populations respond to broad scale effects of land use and climate change.

Arid Ecosystems

Increased precipitation variability decreases grass productivity and increases shrub productivity

Gherardi, L. A., & Sala, O. E. (2015). Enhanced interannual precipitation variability increases plant functional diversity that in turn ameliorates negative impact on productivity. Ecology letters.

The impacts of projected variation in precipitation on functional diversity have received limited attention. Two scientists from Arizona State University examined the impact of increased levels of precipitation on the functional diversity of grass populations using a 6-year rainfall manipulation experiment. Five precipitation treatments were switched annually, resulting in increased levels of precipitation variability while maintaining average precipitation constant. Functional diversity showed a positive response to increased variability due to increased evenness. Dominant grasses decreased and rare plant functional types increased in abundance because grasses showed a hump-shaped response to precipitation with a maximum around modal precipitation, whereas rare species peaked at high precipitation values. Increased functional diversity ameliorated negative effects of precipitation variability on primary production. Rare species buffered the effect of precipitation variability on the variability in total productivity because their variance decreases with increasing precipitation variance.

Biodiversity/Species and Ecosystem Response

Earlier spring onset in the western U.S.

Allstadt, A. J., Vavrus, S. J., Heglund, P. J., Pidgeon, A. M., Thogmartin, W. E., & Radeloff, V. C. (2015). Spring plant phenology and false springs in the conterminous US during the 21st century. Environmental Research Letters, 10(10), 104008.

A new study from the University of Wisconsin examines changes in the onset of spring plant growth. Earlier spring onset may cause phenological mismatches between the availability of plant resources and dependent animals. This could potentially lead to more false springs, when subsequent freezing temperatures damage new plant growth. The authors of this study used the extended spring indices to project changes in spring onset, and predicted false springs through 2100 in the conterminous United States (US) using downscaled climate projections from the Coupled Model Intercomparison Project 5 (CMIP5) ensemble. The median shift in spring onset was 23 days earlier in the Representative Concentration Pathway (RCP) 8.5 scenario with particularly large shifts in the Western US and the Great Plains. Spatial variation in phenology was due to the influence of short-term temperature changes around the time of spring onset versus season-long accumulation of warm temperatures. False spring risk increased in the Great Plains and portions of the Midwest, but remained constant or decreased elsewhere. This study concludes that global climate change may have complex and spatially variable effects on spring onset and false springs, making local predictions of change difficult.

Saving bull trout from a warming climate

A news story about ecologists attempting a radical new method in conservation biology: physically relocating species that will not survive in their current habitat with a rapidly warming climate. Clint Muhlfeld with the USGS is undertaking one of the largest relocation projects to date, moving bull trout populations to higher elevation lakes in Montana. The project is in its early experimental stages and displays a “herculean” scientific effort to save the most vulnerable of trout species from a man-made environmental threat.

Climate and Weather Reports and Services

Evaluation of a regional climate modeling effort for the Western United States using a superensemble:

Sihan Li, Philip W. Mote, David E. Rupp, Dean Vickers, Roberto Mera, and Myles Allen. (2015). Evaluation of a Regional Climate Modeling Effort for the Western United States Using a Superensemble from Weather@home. Journal of Climate, Vol. 28, No. 19 : pp. 7470-7488 (doi: 10.1175/JCLI-D-14-00808.1)

A group of scientists from OSU, the Union of Concerned Scientists, and Oxford compared simulations from a regional climate model (RCM) as part of a superensemble experiment with observational data over the western United States. Overall, the means of seasonal temperature were well represented in the simulations. Additionally, the overall magnitude and spatial pattern of precipitation were well characterized, though somewhat exaggerated along the coastal mountains, Cascade Range, and Sierra Nevada. The simulations also produced regional U.S. weather patterns associated with El Niño. The superensemble simulated the observed spatial pattern of mean annual temperature more faithfully than any of the RCM–GCM pairings in the North American Regional Climate Change Assessment Program (NARCCAP), and its errors in mean annual precipitation fell within the range of errors of the NARCCAP models. Lastly, this paper provided examples of the size of an ensemble required to detect changes at the local level and demonstrated the effect of parameter perturbation on regional precipitation.

NOAA’s Climate Prediction Center releases US Winter Outlook

Forecasters at NOAA’s Climate Prediction Center issued the U.S. Winter Outlook today favoring cooler and wetter weather in Southern Tier states with above-average temperatures most likely in the West and across the Northern Tier. This year’s El Niño, among the strongest on record, is expected to influence weather and climate patterns this winter by impacting the position of the Pacific jet stream.

Coastal/Marine Ecosystems, Ocean Acidification, Sea Level Rise

Abrupt tipping points

Drijfhout, S., Bathiany, S., Beaulieu, C., Brovkin, V., Claussen, M., Huntingford, C., & Swingedouw, D. (2015). Catalogue of abrupt shifts in Intergovernmental Panel on Climate Change climate models. Proceedings of the National Academy of Sciences, 201511451.

One of the most concerning consequences of human-induced increases in atmospheric greenhouse gas concentrations is the potential for rapid regional transitions in the climate system. Yet, despite much public awareness of how “tipping points” may be crossed, little information is available as to exactly what may be expected in the coming centuries. In this study, a group of scientists assessed all Earth System Models underpinning the recent 5th Intergovernmental Panel on Climate Change report and systematically searched for evidence of abrupt changes. The authors found abrupt changes in sea ice, oceanic flows, land ice, and terrestrial ecosystem response, although with little consistency among the models. A particularly large number of abrupt changes was projected for warming levels below 2° C, a warming level commonly acknowledged as safe. The authors discuss mechanisms and include methods to objectively classify abrupt climate change.

Impact of increasing CO2 emissions on the world’s oceans

Nagelkerken, I., & Connell, S. D. (2015). Global alteration of ocean ecosystem functioning due to increasing human CO2 emissions. Proceedings of the National Academy of Sciences, 201510856.

Rising anthropogenic CO2 emissions are anticipated to drive change to ocean ecosystems, but quantitative analyses of this understanding is limited. The authors of this study, Ivan Nagelkerken and Sean D. Connell, compiled 632 published experiments and quantified the direction and magnitude of ecological change resulting from ocean acidification and warming. They found that primary production by temperate, noncalcifying plankton increased with elevated temperature and CO2, whereas tropical plankton productivity decreased from acidification. In addition, secondary production decreased with acidification in both calcifying and noncalcifying species. In summary, Nagelkerken and Connell showed that ocean acidification and warming increased the potential for an overall simplification of ecosystem structure and function with reduced energy flow among trophic levels and little scope for species to acclimate.

Changing El Ninos reduce stability of North American salmon survival rates

D. Patrick Kilduff, Emanuele Di Lorenzo, Louis W. Botsford, and Steven L. H. Teo, Changing central Pacific El Niños reduce stability of North American salmon survival rates, PNAS 2015 112 (35) 10962-10966; published ahead of print August 3, 2015, doi:10.1073/pnas.1503190112

Pacific salmon are a dominant component of the northeast Pacific ecosystem. In this new study, scientists from the Department of Wildlife, Fish and Conservation Biology, UC Davis, and Georgia Tech address the question of how recent changes in ocean conditions will affect populations of two salmon species (coho and Chinook). Since the 1980s, El Niño Southern Oscillation (ENSO) events have been more frequently associated with central tropical Pacific warming (CPW) rather than the canonical eastern Pacific warming ENSO (EPW). CPW is linked to the North Pacific Gyre Oscillation (NPGO), whereas EPW is linked to the Pacific Decadal Oscillation (PDO). Here the authors show that both coho and Chinook salmon survival rates along western North America indicate that the NPGO, rather than the PDO, explains salmon survival since the 1980s. The observed increase in NPGO variance in recent decades was accompanied by an increase in coherence of local survival rates of these two species, increasing salmon variability via the portfolio effect. The portfolio effect is an ecological phenomenon where increased biodiversity leads to increased ecological stability. Such increases in coherence among salmon stocks are usually attributed to controllable freshwater influences such as hatcheries and habitat degradation, but the unknown mechanism underlying the ocean climate effect identified here is not directly subject to management actions.


Vegetation, topography and daily weather influenced burn severity in central Idaho and western Montana forests

Birch, D. S., Morgan, P., Kolden, C. A., Abatzoglou, J. T., Dillon, G. K., Hudak, A. T., & Smith, A. M. (2015). Vegetation, topography and daily weather influenced burn severity in central Idaho and western Montana forests. Ecosphere6(1), art17.

Burn severity is useful for evaluating fire impacts on ecosystems. Scientists infer burn severity using the satellite-derived differenced Normalized Burn Ratio (dNBR). While this is a useful tool, the environmental controls on burn severity across large forest fires are both poorly understood and likely to be different than those influencing fire extent. In this study, scientists from University of Idaho and the USDA in Montana related dNBR to environmental variables including vegetation, topography, fire danger indices, and daily weather for daily areas burned on 42 large forest fires in central Idaho and western Montana. The 353 fire days that were analyzed burned 111,200 ha as part of large fires in 2005, 2006, 2007, and 2011. The researchers found that percent existing vegetation cover had the largest influence on burn severity, while weather variables like fine fuel moisture, relative humidity, and wind speed were also influential but somewhat less important. The authors posit that, in contrast to the strong influence of climate and weather on fire extent, ‘‘bottom-up’’ factors such as topography and vegetation have the most influence on burn severity. While climate and weather certainly interact with the landscape to affect burn severity, pre-fire vegetation conditions due to prior disturbance and management strongly affect vegetation response even when large areas burn quickly.


Trees can take up to four years to return to normal growth rates after a severe drought

Anderegg, W. R. L., Schwalm, C., Biondi, F., Camarero, J. J., Koch, G., Litvak, M., & Pacala, S. (2015). Pervasive drought legacies in forest ecosystems and their implications for carbon cycle models. Science349(6247), 528-532.

The impacts of climate extremes on terrestrial ecosystems are poorly understood but important for predicting carbon cycle feedbacks to climate change. Coupled climate–carbon cycle models typically assume that vegetation recovery from extreme drought is immediate and complete, which conflicts with the understanding of basic plant physiology. In this new study, a team of scientists examined the recovery of stem growth in trees after severe drought at 1,338 forest sites across the globe, comprising 49,339 site-years, and compared the results with simulated recovery in climate-vegetation models. The team found pervasive and substantial “legacy effects” of reduced growth and incomplete recovery for 1 to 4 years after severe drought. Legacy effects were most prevalent in dry ecosystems, among Pinaceae, and among species with low hydraulic safety margins. In contrast, limited or no legacy effects after drought were simulated by current climate-vegetation models. The results of this study highlight hysteresis in ecosystem-level carbon cycling and delayed recovery from climate extremes.

Does climate directly influence Net Primary Productivity globally?

Chu, C., Bartlett, M., Wang, Y., He, F., Weiner, J., Chave, J., & Sack, L. (2015). Does climate directly influence NPP globally?. Global change biology.

A new article published by Global Change Biology refutes the findings of a 2014 study (Michaletz et al. 2014) that concluded that climate change has little to no influence on Net Primary Productivity (NPP). The authors of this paper re-analyzed the same database that was used in the 2014 study to partition the direct and indirect effects of climate on NPP, using three approaches: maximum-likelihood model selection, independent-effects analysis, and structural equation modeling. These new analyses showed that about half of the global variation in NPP could be explained by total stand biomass (Mtot) combined with climate variables and supported strong and direct influences of climate independently of Mtot, both for NPP and for net biomass change averaged across the known lifetime of the stands (ABC = average biomass change). The authors showed that the length of a growing season is an important climate variable, intrinsically correlated with, and contributing to mean annual temperature and precipitation (Tann and Pann). The analyses in this paper provide guidance for statistical and mechanistic analyses of climate drivers of ecosystem processes for predictive modeling and provide novel evidence supporting the strong, direct role of climate in determining vegetation productivity at the global scale.

Larger trees suffer most in drought

Bennett, A.C., McDowell, N.G., Allen, C.D., & Anderson-Teixeria, K.J. (2015). Larger trees suffer most during drought in forests worldwide. Nature Plants 1, Article number: 15139. doi: 10.1038/nplants.2015.139

The frequency of severe droughts is increasing in many regions around the world as a result of climate change. Droughts alter the structure and function of forests. Site- and region-specific studies suggest that large trees, which play keystone roles in forests and can be disproportionately important to ecosystem carbon storage and hydrology, exhibit greater sensitivity to drought than small trees. In this new study, a group of researchers synthesized data on tree growth and mortality collected during 40 drought events in forests worldwide to see whether this size-dependent sensitivity to drought applies more widely. The authors found that droughts consistently had a more detrimental impact on the growth and mortality rates of larger trees. Moreover, drought-related mortality increased with tree size in 65% of the droughts examined, especially when community-wide mortality was high or when bark beetles were present. The more pronounced drought sensitivity of larger trees could be underpinned by greater inherent vulnerability to hydraulic stress, the higher radiation and evaporative demand experienced by exposed crowns, and the tendency for bark beetles to preferentially attack larger trees. The authors of this study suggest that future droughts will have a more detrimental impact on the growth and mortality of larger trees, potentially exacerbating feedbacks to climate change.

Land Use

Water rights pit growth against rivers

Washington may be entering a new era of water rights management, according to this news story from a small town, Yelm, with emerging water rights issues. Yelm is a junior water rights holder whose current method of obtaining enough water from the state is being outgrown by its population. New plans to keep up with Yelm’s population may have negative environmental consequences, particularly on the nearby Nisqually River.

Special Reports / Announcements

OLYMPEX announcement

In a few weeks a veritable army of meteorologists will descend upon the Olympic Mountains of Washington State with radars, aircraft, rain gauges, and other meteorological sensors. All of these resources and participants will be part of the OLYMPEX field program, whose primary goal will be to help NASA evaluate and improve its latest earth-observation satellite: the GPM satellite, which possesses an advanced downward-looking weather radar. But OLYMPEX will be much more, with a huge suite of observing systems that will probably produce the most comprehensive description of clouds and precipitation over any mountain barrier on the planet.

Department of Energy’s Office of Indian Energy soliciting applications from Indian tribes for clean energy projects

The Funding Opportunity Announcement is soliciting applications under two Topic Areas. Topic Area 1: Install clean energy and energy efficiency retrofit projects for tribal buildings, Topic Area 1.a.: Clean Energy Systems, Topic Area 1.b.: Deep Energy Retrofit Energy Efficiency Measures. Topic Area 2: Deploy clean energy systems on a community scale.

Taking Action

Panel to debate long-awaited drought measures

Efforts to pass Western drought legislation are about to be made public as Sen. Lisa Murkowski's (R-Alaska) Energy and Natural Resources Committee holds a long-awaited legislative hearing on the two lead California-specific relief measures. Bills dealing with more preventative drought measures in many other western states are also emerging alongside the two immediate California relief measures. One of prominence is from Washington State Sen. Maria Cantwell. Her legislation (S.1694) authorizes a water-sharing agreement in Washington state’s agriculture-heavy and drought-hit Yakima River Basin. Legislation from other states will likely enter the discussion as well.

Carbon Engineering unveils carbon capture project in Squamish, B.C.

A carbon capturing company called Carbon Engineering, founded by Harvard scientist David Keith and funded by big investors (including Bill Gates), has unveiled their pilot plant in Squamish, B.C. The plant moves large volumes of air through an instrument that absorbs CO2 via a liquid solution and then transforms it into pellets of calcium carbonate. The pellets are then heated to 800 or 900 degrees Celsius and break down, releasing pure carbon. The company plans to further build upon this operation with technology that will turn this pure carbon into renewable fuel. Many groups are already interested in this future product, and the company hopes to scale up their operations to eventually capturing up to one million tonnes of CO2 per day.

Tribal and Indigenous Peoples Matters

Federal appeals judges hear challenges to fish-passage ruling

he most recent development in a long history of litigation between Washington State and Native American tribes: a federal appeals judge will weigh whether Washington State should have to spend billions of dollars to replace culverts that block migrating salmon. The argument is based on mid-19th Century treaties that say tribes don't just have a right to fish but for there to be fish to catch. When culverts are designed in such a way that block salmon from spawning, there are no fish to catch, consequently violating tribal rights. Washington State has said it would need to fix 30 to 40 culverts each year until 2030, spending $155 million annually, to comply, making this a complex and expensive issue.

Tulalip and Swinomish preserve forest and salmon habitat

Two significant environmental initiatives were implemented in the last month. The first was on August 28 at Tulalip, when bulldozers removed about 1,500 linear feet of levee in the Snohomish River’s Qwuloolt Estuary, reopening 350 acres of wetlands to threatened salmon and other species. It’s part of what is reportedly the largest restoration project so far in the Snohomish River watershed. The second initiative was implemented thirty-two miles north, on the Swinomish Reservation, where the Swinomish Tribe and Ecotrust will use a $528,000 three-year grant to develop a forest conservation plan. The plan is being developed with public input and could include carbon sequestration credits, conservation easements and forestland acquisition.

US launches 13 new mini satellites

Thirteen miniature CubeSats, satellites made up of one or more cube-like modules roughly the size of coffee mugs, were launched alongside a classified U.S. spy satellite deployment. Among the 13 new CubeSats was one developed from a Native American college. The satellite, named BisonSat, is the first CubeSat from a Native American college to go to space. BisonSat includes space-based imagery capabilities that will be useful for tribal governments making land use decisions.

Climate change could endanger tribal electric systems

A new report from the U.S. Department of Energy has suggested that heat waves, extreme storms, wildfire and other effects of climate change pose major threats to the electric power systems in Native American communities across the country, most significantly in the West and Southwest. The DOE produced the report to help tribes, especially those such as the Navajo Nation that own and manage many of their power lines, understand the vulnerabilities of their power systems so they can adapt to the risks posed by a warming world. According to the report, tribes across the country are likely to pay more for their electricity as high heat forces residents to use air conditioners more often, increasing demand for electricity. Severe storms and heatwaves are likely to damage power lines more frequently and disrupt the supply of fuel to power plants, causing more frequent power outages. And, extreme heat is likely to reduce the power generation capacity at some power plants because of their inability to keep cool during heatwaves.