EARTH SCIENCES - Notable Research and Discoveries Part 8

1 earth ScienceS different types. Hans-Jörg Vogel of the Helmholtz Centre for Envi-ronmental Research—UFZ in Leipzig, Germany, and Olaf Ippisch at the University of Stuttgart in Germany recently refined models of these flows. Many of these models are based on a mathematical for-mula called Richards’ equation, which is limited in how large an area it accurately models. At large scales—a large section of ground—the model must be broken up into discrete partitions of a certain size, oth-erwise it is inaccurate. Vogel and Ippisch found a way of estimating the size of these partitions so that the models would be correct. The researchers published their findings, “Estimation of a Critical Spatial Discretization Limit for Solving Richards’ Equation at Large Scales,” in a 2008 issue of Vadose Zone Journal. Scientists are also monitoring aquifers to collect even more data. As crucial sources of water for many regions, aquifer depletion would have serious consequences. For example, the largest aquifer in North Ameri-ca, the Ogallala Aquifer, lies under parts of eight American states (Texas, New Mexico, Oklahoma, Colorado, Kansas, Nebraska, Wyoming, and South Dakota). A lot of farms and homes rely on this water. Ogallala’s supply is dwindling, as estimated by the United States Geological Sur-vey (USGS), and although it is continually recharged, replenishment happens slowly and over a limited area. Dennis Gitz of the Agricultural Research Service and his colleagues at Texas Tech University are moni-toring the flow of water through the soil around the aquifer with soil thermometers (the presence of water alters the soil’s temperature). The researchers are focusing on playa lakes—temporary lakes formed when rainwater collects in a cavity—to see if water filtering through the soil at these points is contributing much clean water to the aquifer. If so, then the playa lake region must be maintained and protected. Gitz and his colleagues have begun the study by installing sensors at 14 playa lakes and are preparing to complete 16 others. As the quality of data improves, so will hydrologic models and pre-dictions. Yet researchers may find themselves trying to hit a moving target—any modification in the climate affects the water situation, and the world’s climate seems to be in the midst of substantial changes. ClIMatE CHanGE and WatER Global warming has not been uniform. Some regions, such as the south-eastern United States, have cooled slightly during this time, and some Water Management—conserving an essential resource 1 regions, such as parts of Canada and northern Europe, have warmed at twice the average rate. Scientists—as well as everybody else—would very much like to know what is causing global warming. An important contributor is emissions from factories, automobiles, and other human activities that have increased the amount of greenhouse gases such as carbon diox-ide in Earth’s atmosphere. These gases tend to raise temperatures by absorbing infrared radiation, thereby trapping heat. Attributing most of the recent warming trend to greenhouse gas emissions is a reason-able hypothesis, and many scientists accept it, although it is dificult to prove. Previous warming trends in Earth’s history, such as the one that ended the last of the ice ages about 12,000 years ago, have occurred well before human industry arose. No one is certain what the future climate will be like—Lorenz showed how predictions of complex phenomena such as weather and climate are usually erroneous. How will global climate change affect the planet’s hydrology? Glob-al averages of precipitation have not changed much over the last cen-tury, although there has been variability—some tropical and equatorial regions have experienced less rainfall than usual and other latitudes have had more. But the warming trend has begun to melt a significant amount of ice on and around the polar regions. NASA studies indicate that the Arctic ice thickness has diminished about 40 percent in the last few decades, and glaciers in Greenland and Antarctica are retreating. Losses of sea ice—a thin layer of ice over water—have been severe, with an area of sea ice the size of Norway, Denmark, and Sweden combined having vanished from the Arctic region. The consequences of melting glaciers will be rising sea levels. As water shifts out of the ice reservoir, much of it will end up in the oceans. The additional water will creep up the shores of continents and islands, flooding low-lying areas. Other impacts of global climate change on the water cycle are less certain.Periodicchangesinthepropertiesofoceans,suchasthewarming of El Niño and the cooling of La Niña in the central Pacific Ocean, cor-relatewithdroughtsorstormsinotherpartsoftheworld,evenindistant regions such as the United States. Due to the butterfly effect, nearly any change anywhere in the globe can exert some degree of influence on any other region. Inordertogathercluesonwhattoexpectinthefuture,somescientists are studying the past. For example, searching for the cause of episodes of 10 earth ScienceS extreme weather that have occurred in the past may give some indication ofthefuturecourseofevents.Oneofthemostdisruptiveepisodesinterms ofwaterisadrought.Perhapsthebest-knowndroughtintheUnitedStates and the one with the greatest impact on American history was the long-lastingdroughtassociatedwiththedustbowl. Most scientists use models to study phenomena that take place on a globalscale.Models,suchasthosedescribingEarth’sinterior,asdiscussed in chapter 1, or Earth’s magnetic field, as discussed in chapter 2, distill whatresearchersbelieveistheessence—thecriticalfeatures—oftheprob-lemintoasimplified setofequationsorstructures.Iftheresearchershave correctly identified the essential features, the model reflects the behavior andpropertiesofthephenomenon.Ifnot,themodelismisleading. Siegfried D. Schubert, a researcher at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and his colleagues constructed a climate model based on historical data of sea surface temperatures in the 20th century. The researchers also used another model, developed at NASA, involvingtheatmosphereanditsgeneralcirculation,thefeaturesofwhich came from observations obtained with satellites such as Aqua of clouds and precipitation patterns. A powerful computer simulated the behavior of the models and the time course of the weather patterns and tempera-turesbysolvingthevariousequationsandcrunchingthedata.Withthese tools, Schubert and his colleagues focused on the relation between sea surface temperatures and rainfall in the Great Plains states in the 1930s. El Niño could have played a role in the 1930s drought, and fluctua-tionsintheseasurfacetemperatureinthePacificOceandidoccurduring the 1930s. But these fluctuations were mild and seem insuficient to ac-count for the prolonged drought conditions during the dust bowl. What Schubert and his colleagues discovered was that a slight cooling of tropi-cal Pacific Ocean temperatures coincided with unusually warm tropi-cal Atlantic Ocean temperatures, and this altered the positions of high-velocitywindsintheatmosphere.Thesewindshaveasignificantaffecton temperatures, as they guide or block the movement of air masses. Atmospheric winds can also play a strong role in precipitation. Schubert and his colleagues found that shifts in ocean temperature dur-ing the 1930s altered the flow of a wind system that normally picks up moisture from the Gulf of Mexico. Under typical conditions, this moist air travels over the United States, particularly the Great Plains states, where it cools and falls as rain. Without this moisture, the Great Plains Water Management—conserving an essential resource 11 dried up, and the conditions affecting the wind lasted for an extended period of time, resulting in the devastating length of the 1930s drought. Schubert and his colleagues published their findings, “On the Cause of the 1930s Dust Bowl,” in a 2004 issue of Science. What will global warming, the loss of polar ice, rising sea levels, and other climate changes have on the water cycle and water supplies? Some models suggest a plausible scenario in which the warming trend will result in increased evaporation, which in turn will lead to more precipitation. This would be good news, at least for the reduction in the number and severity of droughts. But a NASA study suggests that the outlook is not necessarily good in terms of precipitation. Michael G. Bosilovich, Schubert, and Gregory K. Walker of the Goddard Space Flight Center used the atmospheric model mentioned above to examine what may happen to the water cycle. Their model also suggests higher precipitation levels, but the increase is over water, not land. While higher temperatures increase evaporation, the warmer air can also hold more water vapor. The model of Bosilovich and his col-leagues predicted higher cycling rates over water than land in general. In other words, the greater evaporation from the seas also fell on the seas in a rapid water cycle, while on land the opposite was true. The researchers published their report, “Global Changes of the Water Cycle Intensity,” in a 2005 issue of the Journal of Climate. No one can be sure at this point what the future will hold, but re-searchers need to continue to improve their models. As the University of Tokyo researchers Taikan Oki and Shinjiro Kanae wrote in Science in August 25, 2006, “Any change in the hydrological cycle will demand changes in water resource management, whether the change is caused by global warming or cooling, or by anthropogenic or natural factors. If society is not well prepared for such changes and fails to monitor varia-tions in the hydrological cycle, large numbers of people run the risk of living under water stress or seeing their livelihoods devastated by water-related hazards such as floods.” ConCluSIon Uncertainties in the future of Earth’s water supplies are mirrored in the uncertainties and gaps in the scientific understanding of the water cycle. Most of the world’s water is salty and undrinkable without desalination, 1 earth ScienceS which is an expensive procedure. Burgeoning populations, along with a rise in pollution, may result in unsustainable demands on freshwater sources such as rivers and aquifers. Innovations to increase water efi-ciency help ease the burden, but conservation and management of water sources are imperative. The extent to which conservation and management must go to pro-tect these water resources depends on the effects climate change may exert. If disruptions in weather patterns cause an increase in the num-ber of areas experiencing prolonged drought or storms and flooding, strict measures may have to be taken. These measures may include re-strictions on supplies and use, which in certain parts of the world must already be instituted from time to time. For example, during water shortages experienced in 2008, residents of Cyprus—an island nation located in the eastern Mediterranean Sea that has been averaging only 18.4 inches (46 cm) of rain a year for the last three decades—had their water cut off on certain days in order to ration the meager supply. Using a water hose for washing patios or cars was prohibited. A better understanding of large-scale phenomena such as the world’s water cycle requires extensive observations. A model running on a computer can simulate global weather patterns and predict what the future may entail, but the predictions will invariably be wrong un-less the data and conditions used in the simulation are highly accurate. To make observations on a worldwide scale, the best tool is a sat-ellite. Orbiting high above the planet, sensitive instruments on board the satellite can watch over vast swaths of land, water, and atmosphere. Aqua and similar satellites have been useful, but more satellites are needed. NASA announced in the spring of 2008 that it plans to launch a satellite in December 2012 to map soil moisture. Scientists presently do not have any means of monitoring soil moisture globally, so they have to rely on samples taken at a few scattered points. Soil moisture has strong effects on evaporation and the water cycle and is a key feature in the cycling of carbon (organic material) and stored energy. An 19.7-foot (6-m) antenna will survey areas 620 miles (1,000 km) wide at a time and examine the entire globe every few days. Worldwide measurements of soil moisture will greatly aid climate and hydrologic models. This data, along with fast computers and the skill and knowledge of researchers, will improve the accuracy of weather and water cycle models. Although the butterfly effect remains a serious impediment, ... - --nqh--