http://www.news.wisc.edu/13307.html

Scientists suspect that the urban heat island effect may be one of the factors behind several studies showing that cities influence rainfall in their surrounding area. The heating of the surface and the overlying air creates instability in the atmosphere that encourages air to rise. As it rises, it cools, and water vapor condenses into rain that falls downwind of the city. Since the launch of the Tropical Rainfall Measuring Mission satellite—a joint NASA-Japanese mission—, observations of rainfall in the Studies of regional rainfall patterns in the U.S. Southeast have shown that rainfall downwind of major urban areas can be as much as 20 percent greater than it is upwind areas. To learn more about how the urban heat island and other city traits such as pollution and topography may be influencing rainfall, please read the feature story Urban Rain.

http://earthobservatory.nasa.gov/Newsroom/

http://earthobservatory.nasa.gov/Newsroom/NewImages/images_index.php3

Vegetation and Rainfall in the Sahel

* High-resolution Images Vegetation March 2004

* Vegetation September 2004

* Rainfall March 2004

* Rainfall September 2004

* Animations: low-resolution (4.8 MB QuickTime)

* high-resolution (8.8 MB QuickTime)

Between the vast sands of the Sahara Desert and the dense foliage of the Congo Rainforest stretches a band of semi-arid grassland. Known as the Sahel, this hardy landscape is one of Africa’s most productive crop regions. Despite its productivity, the Sahel has a dark history of famine tied to highly erratic rainfall. Starting in the early 1970s, a string of dry years drove millions to starvation across the Sahel from Ethiopia in the east to Mauritania in the west. The dry period lasted until the mid-1990s, leaving many to wonder if the Sahara was creeping south, swallowing the arable land in the Sahel. Ground studies identified farmland that had been irreversibly transformed into non-arable land. Some extrapolated from these studies to suggest that the entire Sahel was becoming desert, but the area was far too vast to conduct the extensive ground measurements that would be needed to find out if the Sahel was becoming a desert.

Instead, scientists are using satellite images such as these vegetation index images along with rainfall data to determine if the Sahel can still support plant life. Desertification is the process through which productive land (land that supports vegetation) becomes permanently non-productive (on a human time scale). Many things can cause desertification including human factors like overgrazing or other land use that leads to soil erosion or natural factors like a shift in rainfall. Desertification can be identified in satellite images by comparing rainfall to vegetation growth. If plants grow after rain falls, then the land is still productive and desertification has not happened. If plants fail to grow after rain, then the land might have become non-productive. If plants fail to grow after several years of rainfall, then the change may be permanent, and the land has been desertified.

In 2006, the Global Inventory Modeling and Mapping Studies (GIMMS) group, led by Compton Tucker at Goddard Space Flight Center, released a twenty-four-year-long satellite-based vegetation record of Africa’s Sahel. The vegetation index records the amount of photosynthesis that is happening on the ground, which is a direct measure of how much plants are growing. Studied in conjunction with rainfall, the vegetation record reveals that plants in the Sahel still grow when the region receives rainfall.

These images contrast March 2004, during the dry season, with September 2004, during the rainy season. The top images show the vegetation index while the lower images show rainfall during the same period. The Sahara Desert paints a white streak along the top of the vegetation index image, indicating that few or no plants were growing. Along the bottom of the vegetation index images, the densely vegetated Congo Rainforest is dark green. In between the two, the color in the Sahel swings from tan during the dry season to dark green during the rainy season. The densest vegetation correlates well with areas of heavy rainfall, shown in dark blue in the lower image. The correlation reveals that the Sahel is not becoming a desert on a large scale, though localized land degradation could be occurring. An animation of the vegetation and rainfall records from 1998 to 2005 shows the dance of the seasons across the Sahel with plant growth moving north as rain falls over the region.

To read more about how satellite images are used to understand desertification in Africa’s Sahel, see Defining Desertification, a new feature article on the Earth Observatory.

(Maps and animation by Robert Simmon and Jesse Allen, based on GIMMS and TRMM data. Photographs courtesy USGS and USAID.)

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Though wind-scoured and virtually barren, the southern Sahara Desert turns out to be a surprising sustainer of life an ocean away—in South America’s Amazon Rainforest. By studying NASA satellite data of the spread of dust across the globe, scientists discovered that more than half of the mineral dust that fertilizes the Amazon soil comes from a single spot in the southern Sahara, a large mountain-rimmed valley called the Bodele Depression.

This photo-like image from NASA’s Aqua satellite on January 2, 2007, shows a dust storm brewing in the valley. A bright streak of dust arcs southwest across the Bodele Depression toward Lake Chad. Dust veils the lower elevations, with the higher elevations of the Jos Plateau and the Adamaoua Mountains peaking out as if through fog. During the Northern Hemisphere winter months, northeasterly winds (Harmattan winds) routinely blow across this part of northern Africa. A gap between the Tibesti and Ennedi Mountains creates a natural wind tunnel that focuses and intensifies the winds across the Bodele Depression. The dust spreads westward across the Atlantic on the easterly trade winds to the Amazon, where it replenishes mineral nutrients that are continually depleted from the soil by the heavy, tropical rains.

Based on satellite data and models, scientists estimate that dust storms such as the one pictured here generate about 0.7 million tons of dust on average during winter days. About half of the 40 million tons of dust that are swept across the Atlantic from the Sahara to the Amazon each year come from the Bodele Depression, a small valley that accounts for only 0.2 percent of the entire Sahara and is only 0.5 percent the size of the Amazon itself. The discovery of this surprisingly large single source of mineral dust raises many fascinating questions about how far-flung parts of the Earth system are connected, including how large the dust reservoir in the Bodele depression is, how long it has been emitting such a huge amount of dust, and how long will it continue to fertilize the Amazon.

The large image provided above has a spatial resolution (level of detail) of 500 meters per pixel. The MODIS Rapid Response Team provides twice-daily subsets of northern Africa in additional resolutions via a clickable map.

* References: Koren, I., Kaufman,Y., Washington, R., Todd, M., Rudich, Y., J Vanderlei, M., and Rosenfeld, D. (2006). The Bodele depression: a single spot in the Sahara that provides most of the mineral dust to the Amazon forest, Environmental Research Letters, 1 (014005), p. 1-5. doi:10.1088/1748-9326/1/1/014005. Available online from Institute of Physics Electronic Journals.

Loops of highly charged particles burst from an active region on the Sun’s surface in this image, taken on December 4, 2006. Among the first images taken by STEREO’s SECCHI/Extreme Ultraviolet Imaging Telescope, the image shows the Sun’s roiling surface and atmosphere at temperatures around one million Kelvin (1.8 million degrees Fahrenheit). The ultraviolet light in this range is not typically visible to the human eye, so it is represented here in blue.

The charged particles, mostly extremely hot protons and electrons, rising from the active region create a strong magnetic field that pulls the particles into the loops seen here. Over time, magnetic stress builds in the Sun’s atmosphere until the energy is released in a massive explosion. The explosion sends a giant cloud of charged particles (a coronal mass ejection) and X-ray solar flares hurtling into space with a force comparable to a billion megaton nuclear bombs. When the charged particles and X-rays bombard the Earth, they can disrupt communications and power systems and are a threat to satellites and astronauts in space. The active regions that produce flares are visible from Earth as Sun spots, but the streaming particles emitting ultraviolet light in this image are only visible from space. Just one week after this image was taken, the Sun spot shown here produced a strong solar flare.

Some coronal mass ejections produce powerful storms that threaten the Earth, while others do not. Understanding the difference between harmful and harmless coronal mass ejections is one of the biggest questions that scientists studying the Sun face. Currently, scientists only see ejections in one dimension from a single instrument, which means that they can’t determine where the charged particles are going or how they travel.

To understand how solar storms travel through the solar systems, scientists need a three-dimensional view of the storms. This view will be provided by the STEREO telescopes launched on October 25, 2006. STEREO consists of Sun observation systems orbiting the Sun in front of and behind the Earth. Just as two separate eyes give humans a three-dimensional view of the world, the views provided by each STEREO system can be combined to provide a three-dimensional view of the Sun. Though the first STEREO images were taken in early December, the two systems won’t be in position to give three dimensional images until April 2007.

Further Reading:

A cyclone is a low-pressure area of winds that spiral inwards. Although tropical storms most often come to mind, these spiraling storms can also form at mid- and high latitudes. Two such cyclones formed in tandem in November 2006. The Moderate Resolution Imaging Spectroradiometer (MODIS) flying onboard NASA’s Terra satellite took this picture on November 20. This image shows the cyclones south of Iceland. Scotland appears in the lower right. The larger and perhaps stronger cyclone appears in the east, close to Scotland.

Cyclones at high and mid-latitudes are actually fairly common, and they drive much of the Earth’s weather. In the Northern Hemisphere, cyclones move in a counter-clockwise direction, and both of the spiraling storms in this image curl upwards toward the northeast then the west. The eastern storm is fed by thick clouds from the north that swoop down toward the storm in a giant "V" shape on either side of Iceland. Skies over Iceland are relatively clear, allowing some of the island to show through. South of the storms, more diffuse cloud cover swirls toward the southeast.

NASA image by Jesse Allen, Earth Observatory. Image interpretation provided by Dave Santek and Jeff Key, University of Wisconsin-Madison.

IN RECORD WILDFIRE SEASON, NOAA SATELLITES AID U.S. FIRE MANAGERS

Jan. 4, 2007 — The 2006 wildfire season in the United States set an all-time record with more than 9.8 million acres burned in more than 96,000 wildfires. NOAA satellites were key in detecting and monitoring the movement of the blazes, providing invaluable information to firefighters on the ground. (Click NOAA satellite image for larger view of wildfire in San Bernardino County, Calif., taken July 12, 2006, at 10:15 a.m. EDT that burned 17,000 acres. Smoke from the fire extends northeast to southern Nevada and western Utah. Click here for high resolution version. Please credit "NOAA.")

Throughout the season, NOAA's two geostationary satellites and two polar-orbiting spacecraft provided more than 200 images each day. The most hectic stretch of last year's season came between July and September, when NOAA satellites detected 98,848 hot spots.

"Satellite detection of fires and hotspots provides valuable information about the location of emerging fire problems," said Heath Hockenberry, the NOAA National Fire Weather Program leader, located at the National Interagency Fire Center in Boise, Idaho. "This information allows on-site fire weather forecasters to remain aware of new fire locations and potential problem areas."

Along with satellite coverage, part of NOAA's operational fire and smoke program includes the Hazard Mapping System, which detects the wildfires and tracks the smoke they produce. HMS, which incorporates both NOAA and NASA satellites, tracks smoke from wildfires occurring throughout all of North America and pinpoints fires that are emitting the most smoke. HMS overlays fire locations with satellite imagery, providing analysts on the ground a high measure of quality control.

"NOAA Incident Meteorologists and fire weather forecasters always need to know where fires are and how they are developing in complex terrain," Hockenberry said. "This information is essential to on-site fire weather forecast accuracy and usefulness."

"The smoke from these fires can be extremely harmful to air quality, which is a threat to health and public safety," said Mary E. Kicza, assistant administrator for the NOAA Satellite and Information Service. "NOAA is committed to providing the satellite coverage and products needed to help save lives and property from dangerous fires."

The NOAA National Weather Service, the U.S. Forest Service, the Environmental

Protection Agency and state and local land and air quality managers use fire

and smoke products produced by the NOAA Satellite and Information Service.

In 2007 NOAA, an agency of the U.S. Commerce Department, celebrates 200 years of science and service to the nation. Starting with the establishment of the U.S. Coast and Geodetic Survey in 1807 by Thomas Jefferson much of America's scientific heritage is rooted in NOAA. The agency is dedicated to enhancing economic security and national safety through the prediction and research of weather and climate-related events and information service delivery for transportation, and by providing environmental stewardship of the nation's coastal and marine resources. Through the emerging Global Earth Observation System of Systems (GEOSS), NOAA is working with its federal partners, more than 60 countries and the European Commission to develop a global monitoring network that is as integrated as the planet it observes, predicts and protects.

Relevant Web Sites

NOAA National Fire Weather Program

NOAA Fire Weather Information Center

NOAA Fire Events Satellite Imagery

NOAA Satellites Portal

Media Contact:

John Leslie, NOAA Satellite and Information Service, (301) 713-1265

How fish species suffer as a result of warmer waters

Ongoing global climate change causes changes in the species composition of marine ecosystems, especially in shallow coastal oceans

The eelpout (Zoarces vivparus).

Click here for more information.

Ongoing global climate change causes changes in the species composition of marine ecosystems, especially in shallow coastal oceans. This applies also to fish populations. Previous studies demonstrating a link between global warming and declining fish stocks were based entirely on statistical data. However, in order to estimate future changes, it is essential to develop a deeper understanding of the effect of water temperature on the biology of organisms under question. A new investigation, just published in the scientific journal Science, reveals that a warming induced deficiency in oxygen uptake and supply to tissues is the key factor limiting the stock size of a fish species under heat stress.

Scientists of the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven investigated the relationship between seasonal water temperature and population density using eelpout (Zoarces viviparus), a fish species from the Southern North Sea. The goal of the study was to identify those physiological processes exhibiting the most immediate response to warming in the field. Comparing ecological field data with laboratory investigations of the eelpout's physiology, the authors were able, for the first time, to demonstrate a direct link between temperature dependent oxygen limitation experienced by the eelpouts and warming induced changes in their population density.

During evolution, animals have specialised on environmental conditions and are often very limited in their tolerance to environmental change. In this context, fish species from the North Sea which experience large seasonal temperature fluctuations, are more tolerant to higher temperatures and display wider thermal windows than, for instance, fishes from polar regions living at constant low temperatures. The latter are able to grow and reproduce only within a very limited thermal tolerance window.

Investigations at the Alfred Wegener Institute show the key importance of oxygen uptake and distribution – through respiration and blood circulation – in setting the animals' thermal tolerance range, in that these processes are optimised to only a limited temperature window. With increasing temperature, the organism's oxygen supply is the first to deteriorate, followed by other biochemical stress responses. Finally, oxygen supply fails entirely, leaving the organism to perish. These results represent a significant step forward towards understanding the mechanisms involved in climate-induced alterations in marine ecosystems.

The paper 'Climate change affects marine fishes through the oxygen limitation of thermal tolerance' is published on January 5, 2007 in the scientific journal Science.

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A bumpy shift from ice house to greenhouse

The transition from an ice age to an ice-free planet 300 million years ago was highly unstable, marked by dips and rises in carbon dioxide, extreme swings in climate and drastic effects on tropical vegetation, according to a study published in the journal Science Jan. 5.

"This is the best documented record we have of what happens to the climate system during long-term global warming following an ice age," said Isabel Montanez, professor of geology at the University of California, Davis, and lead author on the paper. But she added that these findings cannot be applied directly to current global warming trends.

In the mid-Permian, 300 million years ago, the Earth was in an ice age. Miles-thick ice sheets covered much of the southern continent, and floating pack ice likely covered the northern polar ocean. The tropics were dominated by lush rainforests, now preserved as coal beds.

Forty million years later, all the ice was gone. The world was a hot, dry place, vegetation was sparse, soils little more than drifts of wind-blown dust.

"You'd have to be a reptile to want to live there," Montanez said.

Montanez and her co-authors derived records of atmospheric carbon dioxide from ancient soils that have been preserved as rocks, from coal and from fossils of plants. They extracted a record of sea surface temperatures from the fossils of brachiopod shellfish and looked at the extensive records of past plant life from fossils of the ancient rainforests. To see how the glaciers advanced and retreated, they looked at the scars and clues left by ice sheets that once covered the great southern continent of Gondwanaland, which included most of the land masses of the modern southern hemisphere.

They placed statistical constraints on their data with computer modeling by Deb Niemeier, professor of civil and environmental engineering and director of the John Muir Institute of the Environment at UC Davis.

The new data show that throughout millions of years, atmospheric carbon dioxide levels swung back and forth between about 250 parts per million, close to present-day levels, to more than 2,000 parts per million. At the same time, the southern ice sheets retreated as carbon dioxide rose and expanded again when levels fell, a pattern compatible with the idea that greenhouse gases caused the end of the late Paleozoic ice age.

"We can see a pattern of increasing carbon dioxide and increasing temperatures, with a series of rises and dips," Montanez said.

Scientists had assumed that as the climate warmed, a tipping point would be reached at which the ice sheets would melt rapidly and for good. Instead, the new data shows that the climate went back and forth between the extremes. But the overall trend was to warming, and by 260 million years ago, the ice sheets were gone.

Records of fossil plants show rapid changes in tropical plant communities as the climate changed. On scales of a few thousand years, lush forests of tree ferns in cool, wet periods alternated with conifers and other plants adapted to a harsher, drier and warmer climate.

"The Permian greenhouse is the only record we have of the transition from an ice age to an ice-free climate on a vegetated planet," Montanez said. But instead of a smooth shift, the transition occurred in a series of sharp swings between cold and hot conditions, occurring during perhaps a half-million to few million years.

But Montanez pointed out that these results cannot be directly applied to current global warming. The current rise in atmospheric carbon dioxide is occurring throughout a much shorter timescale, for one thing. But the current work does show that such a major change in climate will likely not proceed in small, gradual steps, but in a series of unstable, dramatic swings. While these data cover millions of years, similar events might take place during a much shorter time span.

"Perhaps this is the behavior one should expect when we go through a major climate transition," Montanez said.

Further, the record of fossil plants shows the drastic effects of major climate change on living things. In the modern era, tropical forests are already stressed by human use and settlement, and ecological researchers have recorded species moving north or south, likely driven by current global warming.

###

The other authors on the paper are: Neil Tabor, Southern Methodist University, Dallas, a former graduate student with Montanez; William DiMichele, Smithsonian Museum of Natural History; Tracy Frank, Christopher Fielding, Lauren Birgenheier and Michael Rygel, University of Nebraska-Lincoln; and John Isbell, University of Wisconsin-Milwaukee. The work was funded by the National Science Foundation.

Hotspots of mercury contamination identified in eastern North America

Harmful levels of neurotoxin are detected in fish and birds

A US and Canadian research team surveying mercury contamination in fish and birds in the northeastern United States and southeastern Canada has identified five "hotspots" where concentrations of the element exceed those established for human or wildlife health. The team focused on levels of the potent neurotoxin in yellow perch and common loons, but it also took into account contamination in other fish, birds, and mammals. In addition to these hotspots in New England, New York, and Nova Scotia, the researchers found nine "areas of concern" in these regions and in Quebec and New Brunswick. Findings from the team's analysis are summarized in the January 2007 issue of BioScience.

The hotspots are believed to result from complex processes that move atmospherically released mercury through the environment, and from site-specific characteristics such as the high sensitivity of wetlands and forested areas to mercury inputs. Local sources of mercury are also significant. Although mercury is not directly harmful at ambient levels, it is concentrated up to a millionfold and chemically modified in aquatic food chains, resulting in dangerous levels of methylmercury in some wildlife species. Fish consumption advisories responding to mercury contamination exist in all the states and provinces included in the study, and loons are adversely affected by mercury levels they experience.

The hotspots have implications for "cap and trade" approaches being implemented for regulation of emissions from coal-fired electric power stations, which, along with municipal waste incinerators, are major sources of mercury pollution. Cap and trade approaches seek to reduce the total release of mercury but could lead to static or increased emissions in some areas. Greater deposition of mercury near areas that are highly sensitive to the element or that are already affected by it could raise the risk to people and wildlife that consume fish. There is reason to believe, however, that lowering emissions can reduce risk: an analysis of levels of mercury contamination over time in the Merrimack River watershed suggests that lowered emissions reduced mercury levels in biota within a few years.

The 10-member research team was led by David C. Evers of the BioDiversity Research Institute in Gorham, Maine. The study was based on samples collected over four years by the Northeastern Ecosystem Research Cooperative and made use of 7311 observations for seven species. The study report in BioScience is accompanied by an overview article, written by Charles T. Driscoll of Syracuse University and colleagues, that summarizes current knowledge about mercury contamination in the region; the authors conclude that reductions in mercury emissions beyond those currently under way will be needed to eliminate the element as a health risk to humans or to populations of loons.

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BioScience publishes commentary and peer-reviewed articles covering a wide range of biological fields, with a focus on "Organisms from Molecules to the Environment." The journal has been published since 1964. AIBS is an umbrella organization for professional scientific societies and organizations that are involved with biology. It represents some 200 member societies and organizations with a combined membership of about 250,000.

The research articles in the January 2007 issue of BioScience are as follows:

Mercury Contamination in Forest and Freshwater Ecosystems in the Northeastern United States

Charles T. Driscoll, Young-Ji Han, Celia Y. Chen, David C. Evers, Kathleen Fallon Lambert, Thomas M. Holsen, Neil

Biological Mercury Hotspots in the Northeastern United States and Southeastern Canada

David C. Evers, Young-Ji Han, Charles T. Driscoll, Neil C. Kamman, M. Wing Goodale, Kathleen Fallon Lambert, Thomas M. Holsen, Celia Y. Chen, Thomas A. Clair, and Thomas Butler

Building EDENs: The Rise of Environmentally Distributed Ecological Networks

Joseph M. Craine, Jessamy Battersby, Andrew J. Elmore, and Andrew W. Jones

Employing Philosophical Dialogue in Collaborative Science

Sanford D. Eigenbrode, Michael O’Rourke, J. D. Wulfhorst, David M. Althoff, Caren S. Goldberg, Kaylani Merrill, Wayde Morse, Max Nielsen-Pincus, Jennifer Stephens, Leigh Winowiecki, and Nilsa A. Bosque-Pérez

Merging Precaution with Sound Science under the Endangered Species Act

Daniel J. McGarvey

Constructing a Broader and More Inclusive Value System in Science

María Uriarte, Holly A. Ewing, Valerie T. Eviner, and Kathleen C. Weathers

How trees manage water in arid environments

FOR IMMEDIATE RELEASE

Jan. 2, 2007

BLOOMINGTON, Ind. -- Water scarcity is slowly becoming a fact of life in increasingly large areas.

The summer of 2006 was the second warmest in the continental United States since records began in 1895, according to the National Climatic Data Center. Moderate to extreme drought conditions were evident in about 40 percent of the country.

Constance Brown

Print-Quality Photo

When Constance Brown moved from Arizona to Indiana two years ago, she was struck by a major difference: people in Indiana don't think about water every day the way people in Arizona do.

The difference shows up in many ways. In Arizona, Brown said, if you drop a piece of ice on the kitchen floor and ignore it, in a few minutes it will be gone -- melted and then evaporated. In Indiana, if you drop a piece of ice on the floor and ignore it, the water will just stay there until it's wiped up.

In Arizona, she said, if you need a particular garment on short notice and it's in the laundry, you can wash it by hand and hang it outside. It will be dry in 15 minutes. Not in Indiana.

In semi-arid environments such as the southwestern United States, humidity is so low that water is scarce to begin with and hard to hold onto when there is a rare cloudburst. Rain that collects in puddles is quickly sucked up by evaporation into the dry air. Most of the rest runs off before it can soak into the ground. Maintaining an adequate supply of water is a constant challenge, and water management is a top priority.

One way to make better use of scarce water resources would be to retain more of the water that falls during a heavy rain. To accomplish this, better understanding is needed about how water behaves in the environment. Brown, a micrometeorologist in the Atmospheric Science Program of Indiana University's Department of Geography, is one of the scientists working to provide this understanding. Her research is primarily funded by the National Science Foundation.

A tower from which measurements of trees were made

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In a forthcoming paper in the Journal of Arid Environments, which is available on the Web at http://authors.elsevier.com/offprints/YJARE1769/0dee34d6306f9059b870583e03a193bd, she reports the first results of a study designed to characterize the surface exchanges of water and carbon dioxide in a forest in the Santa Catalina Mountains near Tucson, Ariz. Mountain forests are an important source of water for the rest of such semi-arid regions, and these forests provide relatively isolated conditions where scientists can get a clearer picture of what is happening to the water that so many people depend on. In a desert region, such forests are found only at the tops of mountains because only there does precipitation exceed evaporation enough for forest vegetation to survive.

Understanding surface-atmosphere interactions is important to understanding a range of water resource phenomena including predictions about water supplies, Brown said. "This research seeks to characterize the explicit relationship between water availability and photosynthetic activities of the vegetation. This paper is the first step in that process, and it illustrates the seasonal characteristics of the forest vegetation-water relationship as observed during a three-year period during which there were extreme drought conditions in the semi-arid southwestern United States."

Schematic diagram of instruments on tower

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Brown's measurements showed that in this environment, there is a predominant, direct and immediate correspondence between water availability and photosynthetic activity of the vegetation. This is different from what happens in most coniferous forests, where the seasonal behavior of the trees is significantly influenced by temperature changes: the trees are largely dormant in winter and have a summer growing season. The mountain-top forest that she studied was in some ways the opposite.

"During the summer season before the heavy rains, when almost all the winter precipitation had been evaporated and the soil was extremely dry, the trees essentially closed down," she said. "This behavior suggests that the trees have little ability to access any moisture present in bedrock fractures. Because a late spring/early summer period without any rain is very common in southern Arizona, the mountain forest must have evolved the capability to survive it. The rapid recovery of this forest when heavy rains begin confirms the tight coupling between the trees and the available soil moisture."

In short, winter has a significant impact on the primary growing season for these mountain trees, because moisture is continually available from rain or snow, the tree root zones don't freeze, and there is enough sunlight for photosynthesis. The trees slow down during the pre-monsoon dry season in May and June when water is scarce, and then quickly respond to the sudden availability of water at the onset of the monsoon in July.

As unlikely as it may seem, Arizona does experience a monsoon every summer. Certain roads have yellow warning signs posted -- "Do Not Cross When Flooded." Though these signs may seem out of place in the middle of a desert, they have a serious purpose. In Arizona, as in other regions of the world such as India, residents must cope with a season of high temperatures, high winds and high moisture, resulting in potentially deadly weather.

The Arizona monsoon usually begins around July 7 and continues for the next two months, resulting in about one-third of the region's yearly rainfall. The monsoon varies from year to year in starting date, duration and intensity.

"The semi-arid forest ecosystem adapts to the extremes in the annual cycle of water availability by its ability to remain turned on during the winter," Brown said. "Water stress, rather than temperature, is the primary control on the forest's behavior. The trees will remain significantly active regardless of the season, providing they have access to moisture."

It remains to be seen whether coniferous forests at lower elevations in the western United States will be able to do the same if they are confronted with prolonged water scarcity.

Media may contact:

IU Media Relations

812-856-3342

Larry MacIntyre, Director

812-856-1172

lmacinty@indiana.edu

Susan Williams, Asst. Director

812-855-8773

sulwilli@indiana.edu

Contact Information

• Constance Brown

Department of Geography

combrown@indiana.edu

812-856-5047

• Hal Kibbey

IU Media Relations

hkibbey@indiana.edu

812-855-0074

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Tuesday, January 2, 2007

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The formidable mountain system of the Alps stretches across much of central Europe, with seven countries claiming portions of the mountains within their borders: Germany, France, Switzerland, Italy, Liechtenstein, Austria, and Slovenia. The glacial landscape of the Bernese Alps, located in southwestern Switzerland, is well illustrated by this astronaut photograph. An astronaut took this picture by looking north-northwest while the International Space Station was over the Mediterranean Sea between Corsica and Italy. This oblique viewing angle imparts a sense of perspective to the image. This type of viewing angle complements nadir,or downward-viewing, imagery of the region. Three of the higher peaks of the central Alps are visible: Jungfrau at 4,158 meters (13,642 feet); Moench at 4,089 meters (13,415 feet); and Eiger at 3,970 meters (13,025 feet).

To the east and south of the Jungfrau is the Aletsch Glacier, clearly marked by dark medial moraines extending along the glacier’s length parallel to the valley axis. The medial moraines are formed from rock and soil debris collected along the sides of three mountain glaciers located near the Jungfrau and Moench peaks. As these flowing ice masses merge to form the Aletsch Glacier, the debris accumulates in the middle of the glacier and is carried along the flow direction. Lake Brienz to the northwest results from the actions of both glacial ice and the flowing waters of the Aare and Lütschine rivers, and has a maximum depth of 261 meters (856 feet). The lake has a particularly fragile ecosystem, as demonstrated by the almost total collapse of the whitefish population in 1999. Possible causes for the collapse include increased water turbidity associated with upstream hydropower plant operations, and reduction of phosphorus—a key nutrient for lake algae, and a basic element of the local food web—due to water quality changes.

Astronaut photograph ISS013-E-77377 was acquired September 5, 2006, with a Kodak 760C digital camera using an 800 mm lens, and is provided by the ISS Crew Earth Observations experiment and the Image Science & Analysis Group, Johnson Space Center. The image in this article has been cropped and enhanced to improve contrast. The International Space Station Program supports the laboratory to help astronauts take pictures of Earth that will be of the greatest value to scientists and the public, and to make those images freely available on the Internet. Additional images taken by astronauts and cosmonauts can be viewed at the NASA/JSC Gateway to Astronaut Photography of Earth.

In western Mauritania, the Sahara Desert extends all the way to the shore of the Atlantic Ocean. At this dramatic transition point lies the Banc d’Arguin National Park. The park encompasses shoreline dunes and small islands, as well coastal swamps, seagrass beds, mudflats, and shallow waters. The life in this park is concentrated in the ocean, where fish, dolphins, and sea turtles are among the inhabitants. Millions of migratory birds winter in the coastal waters; in fact, the park is home to the largest winter concentration of wading birds in the world. Thousands of aquatic birds, such as gray herons and white pelicans, breed there as well. The incredible biodiversity of the marine ecosystem is among the reasons Banc d’Arguin National Park is a UNESCO World Heritage Site.

This image of western Mauritania shows the dramatic contrast between the bright sands of the Sahara Desert (right) and the turquoise color of the shallow water offshore. Most of the brightness of the water likely comes from sandy shoals ("banks") or mudflats that are submerged shallowly enough that their reflective sands can still be seen through the water. Tucked into a few bays and fringing the eastern side of Tidra Island are relict mangrove forests, small remaining fragments of a large estuary that thrived in the area in the Sahara’s distant, wetter past. Today, these relicts are the northernmost mangroves in the eastern Atlantic. The dry land portion of the park is a mixture of desert landscapes, from dark, rocky outcrops, to peach-colored rivers of sand dunes. This scene was captured by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite on December 2, 2006.

* Reference: Banc d’Arguin National Park World Heritage Site

* Central Sahara’s Wet Past, image and caption from NASA’s Visible Earth Website.

NASA image courtesy the MODIS Rapid Response Team, Goddard Space Flight Center

Meltwater from glaciers to the east and west drains into Lake Morari, a large lake that lies at an altitude of 4,521 meters (14,830 feet) on the Tibetan Plateau. A stream on the west side provides the lake’s main inflow. Mud from this river gives the light blue hues to the lake water. The well-formed alluvial fan (image center), built by sediment from the main inflow river, is the reason the lake has formed at this point in the valley. The fan has dammed up the depression now occupied by Lake Morari, which is approximately 7 kilometers (4 miles) wide in this view. The fan forms the curved southern shore of the lake. The apex of the fan lies fully 40 meters (130 feet) above the level of the lake. The change of color and texture on the fan appears to result from a new influx of gray sediment on top of an older fan that had been carved by several channels.

Interestingly, the alluvial fan also acts as the only outlet of the lake, although no obvious outlet channel can be seen in this detailed astronaut photograph captured on September 4, 2006. South of the fan, an outlet river appears as a green surface, possibly due to aquatic vegetation or algae. Altitude measurements show that the outlet river lies many meters below the lake surface. This means that lake water drains slowly through the permeable sediments of the alluvial fan by subsurface flow, roughly following the line of the arrow. Another, smaller alluvial fan in the south constricts this outlet river.

The featured astronaut photograph ISS013-E-76262 was acquired September 4, 2006, with a Kodak 760C digital camera using an 800 mm lens, and is provided by the ISS Crew Earth Observations experiment and the Image Science & Analysis Group, Johnson Space Center. The image in this article has been cropped and enhanced to improve contrast. The International Space Station Program supports the laboratory to help astronauts take pictures of Earth that will be of the greatest value to scientists and the public, and to make those images freely available on the Internet. Additional images taken by astronauts and cosmonauts can be viewed at the NASA/JSC Gateway to Astronaut Photography of Earth.

At an estimated 6,695 kilometers (4,160 miles), the Nile is one of the longest, if not the very longest, river on Earth. Two major tributaries feed the Nile: the Blue Nile, which delivers more water; and the White Nile, which reaches deeper into the heart of Africa. Since Europeans began exploring Africa, controversy has dogged the hunt for the remotest source of the Nile. Beginning in the mid-1800s, Lake Victoria was largely accepted as the source of the White Nile. But generations of explorers continued to push farther into the heart of Africa to discover tributaries of Lake Victoria that would qualify as the Nile’s "true" source. The cartographers at National Geographic Society have generally accepted two sources, one in Rwanda and one in Burundi, but the search and the controversy has continued right up to the present.

In March 2006, a trio of explorers announced they had followed the Nile to its remotest point using Global Positioning System (GPS) devices, and that the river originated in a muddy pool deep in the nearly impenetrable Nyungwe Forest in Rwanda. On June 16, 2006, the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on NASA’s Terra satellite captured this image of Nyungwe Forest and nearby Lake Kivu. In this pseudo-true-color image, blue indicates water, green indicates vegetation, and deep green indicates lush vegetation. The forest stands out from its surroundings thanks to its deeper color. The mountainous terrain near Lake Kivu shows up in this picture in sharp relief.

Nyungwe Forest is actually a national park. Established in 2004, the roughly 970-square-kilometer (375-square-mile) park is home to hundreds of bird, butterfly, and orchid species, as well as dozens of mammal species, including non-human primates.

* Further reading: Nile Explorers Battled Adversity, Tragedy to Find River Source, from National Geographic News.

NASA image created by Jesse Allen, Earth Observatory, using data provided courtesy of the NASA/GSFC/METI/ERSDAC/JAROS, and the U.S./Japan ASTER Science Team.

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