Is it that bad?

By Abrahm Lustgarten, Lauren Kirchner, Amanda Zamora, and ProPublica
26 June 2015

(Scientific American) –

Why do I keep hearing about the California drought, if it's the Colorado River that we're "killing"?

Pretty much every state west of the Rockies has been facing a water shortage of one kind or another in recent years.  California's is a severe, but relatively short-term, drought. But the Colorado River basin—which provides critical water supplies for seven states including California—is the victim of a slower-burning catastrophe entering its 16th year. Wyoming, Colorado, New Mexico, Utah, Nevada, Arizona, and California all share water from the Colorado River, a hugely important water resource that sustains 40 million people in those states, supports 15 percent of the nation's food supply, and fills two of largest water reserves in the country.

The severe shortages of rain and snowfall have hurt California's $46 billion agricultural industry and helped raise national awareness of the longer-term shortages that are affecting the entire Colorado River basin. But while the two problems have commonalities and have some effect on one another, they're not exactly the same thing.

Just how bad is the drought in California right now?

Most of California is experiencing "extreme to exceptional drought," and the crisis has now entered its fourth year. This month, signaling how serious the current situation is, state officials announced the first cutback to farmers' water rights since 1977, and ordered cities and towns to cut water use by as much as 36 percent. Those who don't comply with the cuts will face fines, but some farmers are already ignoring the new rules, or challenging them in court.

The drought shows no sign of letting up any time soon, and the state's agricultural industry is suffering. A recent study by U.C. Davis researchers projected that the drought would cost California's economy $2.7 billion in 2015 alone.

In addition to the economic cost, the drought has subtle and not-so-subtle effects on flora and fauna throughout the region. This current drought may be contributing to the spread of the West Nile virus, and it's threatening populations of geese, ducks, and Joshua trees. Dry, hot periods can exacerbate wildfires, while water shortages are making firefighters' jobs even harder.

And a little bit of rain won't help. NOAA scientists say it could take several years of average or above-average rainfall before California's water supply can return to anything close to normal. [more]

California's Drought Is Part of a Much Bigger Water Crisis

Technorati Tags: California,North America,drought,freshwater depletion,global warming,climate change,agriculture,Colorado River,population

Dead Zone

By Robert Scribbler
5 May 2015

(RobertScribbler.wordpress.com) – The world ocean is now a region of expanding oxygen-deprived dead zones.

It’s an upshot of a human-warmed ocean system filled with high nutrient run-off from mass, industrialized farming, rising atmospheric nitrogen levels, and increasing dust from wildfires, dust storms, and industrial aerosol emissions. Warming seas hold less oxygen in solution. And the nutrient seeding feeds giant algae blooms that, when they die and decompose, further rob ocean waters of oxygen. Combined, the two are an extreme hazard to ocean health — symptoms of a dangerous transition to stratified, or worse, Canfield Ocean states.

In total, more than 405 dead zones now occupy mostly coastal waters worldwide. Covering an area of 95,000 square miles and expanding, these anoxic regions threaten marine species directly through suffocation or indirectly through the growth of toxin-producing bacteria which thrive in low-oxygen environments.

Now, according to new research published in Biogeosciences [pdf], it appears that some of these dead zones have gone mobile.

The report finds zones of very low oxygen covering swirls of surface water 100-150 kilometers in diameter and stretching to about 100 meters in depth. The zones churn like whirlpools or eddies. Encapsulated in their own current of water with oxygen levels low enough to induce fish kills, these ‘dead pools’ have been discovered swirling off the coast of Africa in recent satellite photos. [more]

Ocean Dead Zones Swirl Off Africa, Threatening Coastlines with Mass Fish Kills

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30 April 2015 (EGU) – A team of German and Canadian researchers have discovered areas with extremely low levels of oxygen in the tropical North Atlantic, several hundred kilometres off the coast of West Africa. The levels measured in these ‘dead zones’, inhabitable for most marine animals, are the lowest ever recorded in Atlantic open waters. The dead zones are created in eddies, large swirling masses of water that slowly move westward. Encountering an island, they could potentially lead to mass fish kills. The research is published today in Biogeosciences [pdf], an open access journal of the European Geosciences Union (EGU).

Dead zones are areas of the ocean depleted of oxygen. Most marine animals, like fish and crabs, cannot live within these regions, where only certain microorganisms can survive. In addition to the environmental impact, dead zones are an economic concern for commercial fishing, with very low oxygen concentrations having been linked to reduced fish yields in the Baltic Sea and other parts of the world.

“Before our study, it was thought that the open waters of the North Atlantic had minimum oxygen concentrations of about 40 micromol per litre of seawater, or about one millilitre of dissolved oxygen per litre of seawater,” says lead-author Johannes Karstensen, a researcher at GEOMAR, the Helmholtz Centre for Ocean Research Kiel, in Kiel, Germany. This concentration of oxygen is low, but still allows most fish to survive. In contrast, the minimum levels of oxygen now measured are some 20 times lower than the previous minimum, making the dead zones nearly void of all oxygen and unsuitable for most marine animals.

Dead zones are most common near inhabited coastlines where rivers often carry fertilisers and other chemical nutrients into the ocean, triggering algae blooms. As the algae die, they sink to the seafloor and are decomposed by bacteria, which use up oxygen in this process. Currents in the ocean can carry these low-oxygen waters away from the coast, but a dead zone forming in the open ocean had not yet been discovered.

The newly discovered dead zones are unique in that they form within eddies, large masses of water spinning in a whirlpool pattern. “The few eddies we observed in greater detail may be thought of as rotating cylinders of 100 to 150 km in diameter and a height of several hundred metres, with the dead zone taking up the upper 100 metres or so,” explains Karstensen. The area around the dead-zone eddies remains rich in oxygen.

“The fast rotation of the eddies makes it very difficult to exchange oxygen across the boundary between the rotating current and the surrounding ocean. Moreover, the circulation creates a very shallow layer – of a few tens of meters – on top of the swirling water that supports intense plant growth,” explains Karstensen. This plant growth is similar to the algae blooms occurring in coastal areas, with bacteria in the deeper waters consuming the available oxygen as they decompose the sinking plant matter. “From our measurements, we estimated that the oxygen consumption within the eddies is some five times larger than in normal ocean conditions.”

The eddies studied in the Biogeosciences article form where a current that flows along the West African coast becomes unstable. They then move slowly to the west, for many months, due to the Earth’s rotation. “Depending on factors such as the [eddies’] speed of rotation and the plant growth, the initially fairly oxygenated waters get more and more depleted and the dead zones evolve within the eddies,” explains Karstensen. The team reports concentrations ranging from close to no oxygen to no more than 0.3 millilitres of oxygen per litre of seawater. These values are all the more dramatic when compared to the levels of oxygen at shallow depths just outside the eddies, which can be up to 100 times higher than those within.

The researchers have been conducting observations in the region off the West African coast and around the Cape Verde Islands for the past seven years, measuring not only oxygen concentrations in the ocean but also water movements, temperature and salinity. To study the dead zones, they used several tools, including drifting floats that often got trapped within the eddies. To measure plant growth, they used satellite observations of ocean surface colour.

Their observations allowed them to measure the properties of the dead zones, as well as study their impact in the ecosystem. Zooplankton – small animals that play an important role in marine food webs – usually come up to the surface at night to feed on plants and hide in the deeper, dark waters during the day to escape predators. However, within the eddies, the researchers noticed that zooplankton remained at the surface, even during the day, not entering the low-oxygen environment underneath.

“Another aspect related to the ecosystem impact has a socioeconomic dimension,” says Karstensen. “Given that the few dead zones we observed propagated less than 100 km north of the Cape Verde archipelago, it is not unlikely that an open-ocean dead zone will hit the islands at some point. This could cause the coast to be flooded with low-oxygen water, which may put severe stress on the coastal ecosystems and may even provoke fish kills and the die-off of other marine life.”

Press Release: ‘Dead zones’ found in Atlantic open waters

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ABSTRACT: Here we present first observations, from instrumentation installed on moorings and a float, of unexpectedly low (<2 μmol kg⁻¹) oxygen environments in the open waters of the tropical North Atlantic, a region where oxygen concentration does normally not fall much below 40 μmol kg⁻¹. The low-oxygen zones are created at shallow depth, just below the mixed layer, in the euphotic zone of cyclonic eddies and anticyclonic-modewater eddies. Both types of eddies are prone to high surface productivity. Net respiration rates for the eddies are found to be 3 to 5 times higher when compared with surrounding waters. Oxygen is lowest in the centre of the eddies, in a depth range where the swirl velocity, defining the transition between eddy and surroundings, has its maximum. It is assumed that the strong velocity at the outer rim of the eddies hampers the transport of properties across the eddies boundary and as such isolates their cores. This is supported by a remarkably stable hydrographic structure of the eddies core over periods of several months. The eddies propagate westward, at about 4 to 5 km day⁻¹, from their generation region off the West African coast into the open ocean. High productivity and accompanying respiration, paired with sluggish exchange across the eddy boundary, create the "dead zone" inside the eddies, so far only reported for coastal areas or lakes. We observe a direct impact of the open ocean dead zones on the marine ecosystem as such that the diurnal vertical migration of zooplankton is suppressed inside the eddies.

Open ocean dead zones in the tropical North Atlantic Ocean

Technorati Tags: ocean anoxia,anoxia,dead zone,eutrophication,fish decline

Running out of water

By Nick Janes
16 June 2015

MOUNTAIN HOUSE (CBS13) – The community of Mountain House is days away from having no water at all after the state cut off its only water source.

Anthony Gordon saves drinking water just in case, even though he never thought it would come to this.

“My wife thinks I’m nuts. I have like 500 gallons of drinking water stored in my home,” he said.

The upscale community of Mountain House, west of Tracy, is days away from having no water. It’s not just about lawns—there may not be a drop for the 15,000 residents to drink.

“We’re out there looking for water supplies as we speak,” said Mountain House general manager Ed Pattison. “We have storage tanks, but those are basically just to ensure the correct pressurization of the distribution system. No more than 2 days are in those storage tanks.”

The community’s sole source of water, the Byron-Bethany Irrigation District, was one of 114 senior water rights holders cut off by a curtailment notice from the state on

Disappearing water

The disappearing reservoir: Nasa timelapse reveals how 15 years of climate change and overuse have transformed Lake Powell

• A new Nasa video document changes in the northeastern reaches of Lake Powell between 1999 and 2015
• At the beginning of the series in 1999, water levels were relatively high, and the water was a clear, dark blue
• Today, the reservoir at Arizona-Utah border is 45 per cent below 'full pool' capacity due to West's water crisis

Published: 23:29 GMT, 16 June 2015 | Updated: 00:09 GMT, 17 June 2015

Lake Powell, a meandering reservoir that sits along the border between Arizona and Utah, is a striking reflection of the West's water crisis.

The lake is currently 45 per cent below its capacity, and a severe drought has left a 'bathtub ring' at the bottom of its impressive rock formations.

Now, a timelapse from Nasa has revealed the astounding change that's occurred to the lake in just 15 years as a result of overuse and drought.

View Pictures and Read More At: http://www.dailymail.co.uk/sciencetech/article-3127176/The-disappearing-reservoir-Nasa-timelapse-reveals-15-years-climate-change-overuse-transformed-Lake-Powell.html?printingPage=true

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On the way out

By James Dyke
19 June 2015

(The Conversation) – We are currently witnessing the start of a mass extinction event the likes of which have not been seen on Earth for at least 65 million years. This is the alarming finding of a new study published in the journal Science Advances.

The research was designed to determine how human actions over the past 500 years have affected the extinction rates of vertebrates: mammals, fish, birds, reptiles and amphibians. It found a clear signal of elevated species loss which has markedly accelerated over the past couple of hundred years, such that life on Earth is embarking on its sixth greatest extinction event in its 3.5 billion year history.

This latest research was conducted by an international team lead by Gerardo Ceballos of the National Autonomous University of Mexico. Measuring extinction rates is notoriously hard. Recently I reported on some of the fiendishly clever ways such rates have been estimated. These studies are producing profoundly worrying results.

However, there is always the risk that such work overestimates modern extinction rates because they need to make a number of assumptions given the very limited data available. Ceballos and his team wanted to put a floor on these numbers, to establish extinction rates for species that were very conservative, with the understanding that whatever the rate of species loss has actually been, it could not be any lower.

This makes their findings even more significant because even with such conservative estimates they find extinction rates are much, much higher than the background rate of extinction – the rate of species loss in the absence of any human impacts.

Here again, they err on the side of caution. A number of studies have attempted to estimate the background rate of extinction. These have produced upper values of about one out of every million species being lost each year. Using recent work by co-author Anthony Barnosky, they effectively double this background rate and so assume that two out of every million species will disappear through natural causes each year. This should mean that differences between the background and human driven extinction rates will be smaller. But they find that the magnitude of more recent extinctions is so great as to effectively swamp any natural processes. [more]

Earth’s sixth mass extinction has begun, new study confirms

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ABSTRACT: The oft-repeated claim that Earth’s biota is entering a sixth “mass extinction” depends on clearly demonstrating that current extinction rates are far above the “background” rates prevailing in the five previous mass extinctions. Earlier estimates of extinction rates have been criticized for using assumptions that might overestimate the severity of the extinction crisis. We assess, using extremely conservative assumptions, whether human activities are causing a mass extinction. First, we use a recent estimate of a background rate of 2 mammal extinctions per 10,000 species per 100 years (that is, 2 E/MSY), which is twice as high as widely used previous estimates. We then compare this rate with the current rate of mammal and vertebrate extinctions. The latter is conservatively low because listing a species as extinct requires meeting stringent criteria. Even under our assumptions, which would tend to minimize evidence of an incipient mass extinction, the average rate of vertebrate species loss over the last century is up to 114 times higher than the background rate. Under the 2 E/MSY background rate, the number of species that have gone extinct in the last century would have taken, depending on the vertebrate taxon, between 800 and 10,000 years to disappear. These estimates reveal an exceptionally rapid loss of biodiversity over the last few centuries, indicating that a sixth mass extinction is already under way. Averting a dramatic decay of biodiversity and the subsequent loss of ecosystem services is still possible through intensified conservation efforts, but that window of opportunity is rapidly closing.

Accelerated modern human–induced species losses: Entering the sixth mass extinction

Technorati Tags: biodiversity,wildlife,extinction,mass extinction,mammal decline,bird decline,amphibian decline

Backup water in trouble

Irvine, California, 16 June 2015 (UCI) – Two new studies led by UC Irvine using data from NASA Gravity Recovery and Climate Experiment satellites show that human consumption is rapidly draining some of its largest groundwater basins, yet there is little to no accurate data about how much water remains in them.

The result is that significant segments of Earth’s population are consuming groundwater quickly without knowing when it might run out, the researchers conclude. The findings appear today in Water Resources Research. [“Quantifying renewable groundwater stress with GRACE” and “Uncertainty in global groundwater storage estimates in a total groundwater stress framework”.]

“Available physical and chemical measurements are simply insufficient,” said UCI professor and principal investigator Jay Famiglietti, who is also the senior water scientist at NASA’s Jet Propulsion Laboratory. “Given how quickly we are consuming the world’s groundwater reserves, we need a coordinated global effort to determine how much is left.”

The studies are the first to characterize groundwater losses via data from space, using readings generated by NASA’s twin GRACE satellites that measure dips and bumps in Earth’s gravity, which is affected by the weight of water.

For the first paper, researchers examined the planet’s 37 largest aquifers between 2003 and 2013. The eight worst off were classified as overstressed, with nearly no natural replenishment to offset usage. Another five aquifers were found, in descending order, to be extremely or highly stressed, depending upon the level of replenishment in each – still in trouble but with some water flowing back into them.

The most overburdened are in the world’s driest areas, which draw heavily on underground water. Climate change and population growth are expected to intensify the problem.

“What happens when a highly stressed aquifer is located in a region with socioeconomic or political tensions that can’t supplement declining water supplies fast enough?” asked the lead author on both studies, Alexandra Richey, who conducted the research as a UCI doctoral student. “We’re trying to raise red flags now to pinpoint where active management today could protect future lives and livelihoods.”

The research team – which included co-authors from NASA, the National Center for Atmospheric Research, National Taiwan University and UC Santa Barbara – found that the Arabian Aquifer System, an important water source for more than 60 million people, is the most overstressed in the world.

The Indus Basin aquifer of northwestern India and Pakistan is the second-most overstressed, and the Murzuk-Djado Basin in northern Africa is third. California’s Central Valley, utilized heavily for agriculture and suffering rapid depletion, was slightly better off but still labeled highly stressed in the first study.

“As we’re seeing in California right now, we rely much more heavily on groundwater during drought,” Famiglietti said. “When examining the sustainability of a region’s water resources, we absolutely must account for that dependence.”

In a companion paper published today in the same journal, the scientists conclude that the total remaining volume of the world’s usable groundwater is poorly known, with often widely varying estimates, but is likely far less than rudimentary estimates made decades ago.

By comparing their satellite-derived groundwater loss rates to what little data exists on groundwater availability, they found major discrepancies in projected “time to depletion.” In the overstressed Northwest Sahara Aquifer System, for example, this fluctuated between 10 and 21,000 years.

“We don’t actually know how much is stored in each of these aquifers. Estimates of remaining storage might vary from decades to millennia,” Richey said. “In a water-scarce society, we can no longer tolerate this level of uncertainty, especially since groundwater is disappearing so rapidly.”

The study notes that the dearth of groundwater is already leading to significant ecological damage, including depleted rivers, declining water quality, and subsiding land.

Groundwater aquifers are typically located in soil or deeper rock layers beneath Earth’s surface. The depth and thickness of many make it tough and costly to drill to or otherwise reach bedrock and learn where the moisture bottoms out. But it has to be done, according to the authors.

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A third of the world’s biggest groundwater basins are in distress

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ABSTRACT: Groundwater is an increasingly important water supply source globally. Understanding the amount of groundwater used versus the volume available is crucial to evaluate future water availability. We present a groundwater stress assessment to quantify the relationship between groundwater use and availability in the world's 37 largest aquifer systems. We quantify stress according to a ratio of groundwater use to availability, which we call the Renewable Groundwater Stress ratio. The impact of quantifying groundwater use based on nationally reported groundwater withdrawal statistics is compared to a novel approach to quantify use based on remote sensing observations from the Gravity Recovery and Climate Experiment (GRACE) satellite mission. Four characteristic stress regimes are defined: Overstressed, Variable Stress, Human-dominated Stress, and Unstressed. The regimes are a function of the sign of use (positive or negative) and the sign of groundwater availability, defined as mean annual recharge. The ability to mitigate and adapt to stressed conditions, where use exceeds sustainable water availability, is a function of economic capacity and land use patterns. Therefore, we qualitatively explore the relationship between stress and anthropogenic biomes. We find that estimates of groundwater stress based on withdrawal statistics are unable to capture the range of characteristic stress regimes, especially in regions dominated by sparsely populated biome types with limited cropland. GRACE-based estimates of use and stress can holistically quantify the impact of groundwater use on stress, resulting in both greater magnitudes of stress and more variability of stress between regions.

Quantifying renewable groundwater stress with GRACE

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ABSTRACT: Groundwater is a finite resource under continuous external pressures. Current unsustainable groundwater use threatens the resilience of aquifer systems and their ability to provide a long-term water source. Groundwater storage is considered to be a factor of groundwater resilience, although the extent to which resilience can be maintained has yet to be explored in depth. In this study, we assess the limit of groundwater resilience in the world's largest groundwater systems with remote sensing observations. The Total Groundwater Stress (TGS) ratio, defined as the ratio of total storage to the groundwater depletion rate, is used to explore the timescales to depletion in the world's largest aquifer systems and associated groundwater buffer capacity. We find that the current state of knowledge of large-scale groundwater storage has uncertainty ranges across orders of magnitude that severely limit the characterization of resilience in the study aquifers. Additionally, we show that groundwater availability, traditionally defined as recharge and re-defined in this study as total storage, can alter the systems that are considered to be stressed versus unstressed. We find that remote sensing observations from NASA's Gravity Recovery and Climate Experiment can assist in providing such information at the scale of a whole aquifer. For example, we demonstrate that a groundwater depletion rate in the Northwest Sahara Aquifer System of 2.69 ± 0.8 km³ per year would result in the aquifer being depleted to 90% of its total storage in as few as 50 years given an initial storage estimate of 70 km³ [Swezey, 1999].

Uncertainty in global groundwater storage estimates in a total groundwater stress framework

Technorati Tags: freshwater depletion,agriculture,NASA,GRACE,population,global warming,climate change,India,California,drought,Pakistan,Africa

Dry lakes

By Vanessa Dezem
15 June 2015

(Bloomberg) – After drought pushed São Paulo to the verge of severe water rationing, late summer rains gave the state-run utility Sabesp, Brazil’s biggest water provider, a second chance to fix infrastructure that city officials blamed for the crisis. With the dry season starting, it’s a rush against time to divert rivers and connect lakes before reservoirs run low again.

The time squeeze highlights the precarious situation that South America’s largest metropolis is in after two decades without any major new water projects. Reservoirs still haven’t recovered from last year’s drought and forecasters are calling for hotter months ahead because of the El Niño weather pattern.

“Infrastructure wasn’t Sabesp’s priority in recent years – it didn’t take steps to avoid the crisis,” said Pedro Caetano Mancuso, director at the Center for Water Safety at the University of Sao Paulo. “Even though Sabesp is willing to do the work now, whether or not it’s completed on time to avoid an even bigger problem is the big question.”

Sabesp has said it was the severity of last year’s drought and not a lack of infrastructure investments at Latin America’s largest publicly traded water utility that led to the crisis.

“We were prepared for a drought that was as bad as 1953” when Sabesp faced a similar crisis, Chief Executive Officer Jerson Kelman told city council members in a May 13 hearing. “What happened in 2014 was that we got half that amount of rainfall. We weren’t prepared for that.”

São Paulo’s City Council in a June 10 report blamed Sabesp for the crisis that cut off water to some neighborhoods, calling the water shortage “predictable.”

“If Sabesp had invested the dividends it paid to shareholders in New York in projects to modernize systems and to maintain networks, we wouldn’t be in this situation,” said Laercio Benko, the council member who led the commission to investigate the shortage.

The largest of the infrastructure projects that the state-run utility needs this year to guarantee drinking supplies is late. The project to connect the Pequeno River to the Billings reservoir, originally scheduled to be finished in May, won’t be done until August because of environmental and land-use permit delays, Sabesp’s press office said in an e-mailed response to questions. If completed this year, the package of five emergency works Sabesp is pushing through should be enough to avoid rationing, the utility said.

Without the projects and if rainfall comes in at or below last year’s level, Sabesp forecasts its largest reservoir -- known as Cantareira -- could dry up by August, according to internal company forecasts provided by Sabesp to the government and obtained by Bloomberg News. In the company’s worst-case scenario, water could be shut off to most of the Sao Paulo metropolitan area five days a week, according to the document, which was prepared as part of an emergency contingency plan.

Sabesp said in the e-mail that rainfall so far this year has been positive.

As Sabesp accelerates investments now, it’s cutting back elsewhere and raising water prices. The company, whose full name is Cia. de Saneamento Basico do Estado de São Paulo, is cutting by half spending on sewage collection and treatment this year, executives said on a conference call with investors in April. The rate increase reflects Sabesp’s “financial stress,” Chief Financial Officer Rui Affonso said on the call. [more]

Stubborn Brazil Water Crisis Pushes Sabesp to Fix Infrastructure

Technorati Tags: Brazil,South America,drought,freshwater depletion,infrastructure failure,global warming,climate change,deforestation

Trees don’t like Drought

By Julie Cohen
9 June 2015

(UCSB) – A combination of drought, heat and insects is responsible for the death of more than 12 million trees in California, according to a new study from UC Santa Barbara’s National Center for Ecological Analysis and Synthesis (NCEAS). Members of the NCEAS working group studying environmental factors contributing to tree mortality expect this number to increase with climate change.

The study is the first of its kind to examine the wide spectrum of interactions between drought and insects. Lead author William Anderegg, a postdoctoral researcher at the Princeton Environmental Institute, and his coauthors first devised a framework to look at the effects that each stressor can have on tree mortality and then examined interactions among them. The researchers’ findings appear in New Phytologist.

“We wanted to be able to get a sense of how these die-off patterns will shift with climate change,” explained study coauthor Naomi Tague, an associate professor at UCSB’s Bren School of Environmental Science & Management. “Are there huge forests that will be at higher risk of dying sooner?”

The western U.S. has been a hotspot for forest die-offs. Local economies in states like California and Colorado are highly dependent on the nature-based tourism and recreation provided by forests, which offer a scenic backdrop to the skiing, fishing and backpacking opportunities that draw so many people to live and play in the West. But lingering drought, rising temperatures and outbreaks of tree-killing pests such as bark beetles have spurred an increase in widespread tree mortality — especially within the past decade.

“Very often both drought and insects together are responsible for tree mortality,” explained Anderegg, “but there are several good examples of trees dying because of one impact and not the other. We’ve worked to detail the spectrum of interactions between drought and insects and examine how they go hand in hand to affect tree die-offs.”

Forest mortality has also been shown to impact everything from real estate to clean water. Property values in Colorado plummeted after swaths of coniferous forests were damaged by pine beetle infestations. Water purification services provided by forests continue to be disrupted when hectares of forests are lost to pests and drought. What’s more, forest die-off events are projected to increase in frequency and severity in the coming decades.

“If we want to account for forest die-off events at local and global scales, we need some way of estimating how often they are likely to occur,” Tague said. “We’re putting together the pieces of how climate conditions can affect that mortality and how to identify the specific stressors that cause it.”

The study’s framework is a first step toward developing the tools that resource managers need to better predict the impacts of climate change on forests. Scientists and forest specialists are now tasked not only with determining what conditions prompt tree mortality but also how they will shape forested landscapes in the years to come. Being able to predict forest mortality in a changing climate is key to conservation and land use planning.

“Ultimately, forests are a critical part of western U.S. landscapes and state economies,” Anderegg said. “They are also a canary in the coal mine for climate change. These massive forest die-offs that we are starting to see are a sign that climate change is already having major impacts in our backyard.”

Predicting Tree Mortality

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ABSTRACT: Climate change is expected to drive increased tree mortality through drought, heat stress, and insect attacks, with manifold impacts on forest ecosystems. Yet, climate-induced tree mortality and biotic disturbance agents are largely absent from process-based ecosystem models. Using data sets from the western USA and associated studies, we present a framework for determining the relative contribution of drought stress, insect attack, and their interactions, which is critical for modeling mortality in future climates. We outline a simple approach that identifies the mechanisms associated with two guilds of insects – bark beetles and defoliators – which are responsible for substantial tree mortality. We then discuss cross-biome patterns of insect-driven tree mortality and draw upon available evidence contrasting the prevalence of insect outbreaks in temperate and tropical regions. We conclude with an overview of tools and promising avenues to address major challenges. Ultimately, a multitrophic approach that captures tree physiology, insect populations, and tree–insect interactions will better inform projections of forest ecosystem responses to climate change.

Tree mortality from drought, insects, and their interactions in a changing climate

Technorati Tags: plant decline,deforestation,California,North America,drought,global warming,climate change,heat wave,invasive species,ecosystem disruption,habitat loss