Droughts have many different causes. Global oceanic and atmospheric circulation patterns undergo frequent shifts that affect large parts of the globe, particularly those arid and semiarid parts affected by Hadley Cell circulation. One of the better known variations in global circulation is known as the El Nino-Southern Oscillation. Fluctuations in global circulation can account for natural disasters, including the Dust Bowl days of the 1930s in the U.S. plains states. Similar global climate fluctuations may explain the drought, famine, and desertification of parts of the Sahel and the great famines of Ethiopia and Sudan in the 1970s, 1980s, and mid-2000s. Much of Africa, including the Sahel region, has become increasingly dry and desert-like over the past 100 years or more, and any attempts to restart agriculture and repopulate regions evacuated during previous famines in this region may be fruitless and lead to further loss of life.
Hadley Cells are the name given to the globe-encircling belts of air that rise along the equator, dropping moisture as they rise in the tropics. As the air moves away from the equator, it cools and becomes drier, then descends at 15-30° N and S latitude, where it either returns to the equator or moves poleward. The locations of the Hadley Cells move north and south annually, in response to the changing apparent seasonal movement of the Sun. High-pressure systems form where the air descends, and stable clear skies and intense evaporation characterize these because the air is so dry. Another pair of major global circulation belts is formed as air cools at the poles and spreads toward the equator. Cold polar fronts form where the polar air mass meets the warmer air that has circulated around the Hadley Cell from the tropics. In the belts between the polar front and the Hadley Cells, strong westerly winds develop. The position of the polar front and extent of the west-moving wind is controlled by the position of the polar jet stream (formed in the upper troposphere), which is partly fixed in place in the Northern Hemisphere by the high Tibetan Plateau and the Rocky Mountains. Dips and bends in the jet stream path are known as Rossby Waves, and these partly determine the location of high- and low-pressure systems. These Rossby Waves tend to be semi-stable in different seasons, and have predictable patterns for summer and winter. If the pattern of Rossby Waves in the jet stream changes significantly for a season or longer, it may cause storm systems to track to different locations than normal, causing local droughts or floods. Changes to this global circulation may also change the locations of regional downwelling cold dry air. This can cause long-term drought and desertification. Such changes may persist for periods of several weeks, months, or years and may explain several of the severe droughts that have affected Asia, Africa, North America, and elsewhere.
The El Niño-Southern Oscillation air circulation phenomenon can also have strong influences on the locations and strength of drought conditions and desertification of stressed lands. Hadley Cells migrate north and south with summer and winter, shifting the locations of the most intense heating. The switching between ENSO, La Niña, and normal ocean-atmospheric circulation patterns has profound effects on global climate and the migration of different climate belts on yearly to decadal time scales and is thought to account for about a third of all the variability in global rainfall. ENSO events may cause flooding in the western Andes and southern California and a lack of rainfall in other parts of South America including Venezuela, northeastern Brazil, and southern Peru. Analysis of past climate and circulation data has suggested the El Niño-Southern Oscillation was at least partly to blame for the dust bowl days of the 1930s across much of the central and western United States.
Drought and Desertification in the Sahel and Sub-Saharan Africa
The Sahel region offers one of the world's most tragic examples of how poorly managed agricultural practices, politics, and religious differences, when mixed with long term drought conditions, can lead to disaster and permanent desertification. A similar lesson is found in the Rajputana desert of India, one of the cradles of civilization that has become desert because of poor land use coupled with natural drought cycles.
CHINA'S EFFORT TO HALT EXPANSION OF THE GOBI DESERT
China's agriculture, economy, industry, population, and personal wealth have been growing at a remarkable rate. From 1950 to 1998 the grain production in China grew from 90 million tons to 392 million tons, fueling this growth. However, some trends in climate are starting to threaten this growth, and the Chinese government is making huge efforts to counteract these potentially negative trends. After 2003, the grain harvest began declining because of water shortages in the northern and western parts of the country, where the wheat crops have been suffering drought and expansion of the Gobi Desert. The loss of arable land is due to expansion of the desert as well as loss of irrigation water and the changing of farm lands into other uses. A mass migration of the people of China from rural farmlands in the west and center of the country to the relatively wealthy east has also resulted in a loss of farm labor, further decreasing the crop yields.
China has been actively seeking ways to slow the expansion of the Gobi Desert, estimated to be growing at 4,000 square miles (10,360 km2) per year. Massive tree planting campaigns have been mounted, trying to slow the shifting of the sands into existing farm lands. Diversions of water from the humid south to the north of the country are underway, representing some of the most massive waterworks projects in the world. Groundwater resources are being sought for irrigation, and the Chinese government is investing billions of dollars into trying to halt the expansion of the desert, making it one of the nation's top priorities in 2007. Still, the trends in loss of farmland and migration of farm workers to eastern industrial cities means that China needs to make the transition from a grain-producing and exporting country to a grain importer. The scale of the expected grain imports is huge, as the 1.4 billion people in China will need to turn to the United States, the world's largest grain exporter, to purchase food. This will drive up the price of food in the United States but bring the two countries economically much closer.
The Climate Change 2007 report issued by the Intergovernmental Panel on Climate Change has some predictions for China. With rising temperatures, China has been experiencing more warming in the winter than the summer and is seeing a more rapid increase in the minimum temperatures, while the daily maximum temperatures remain about the same. The annual rains are decreasing in northeast and northern China, while increasing in westernmost China, along the Changjiang River, and along the southeast coast. Short duration heat waves have been increasing in frequency, and intense rains and floods are becoming more frequent in western and southern China, especially along the Changjiang River, while summer rains are becoming more steady in eastern China. Northern China is experiencing a decrease in intense rainfall events. The Gobi Desert is continuing to expand toward the Beijing area, including Hebei and Shanxi Provinces, Inner Mongolia, and northern China, with frequent dust storms. The southeastern coastal region of China is seeing a strong increase in the number of typhoons that affect the region, many with extreme storm surges that move into coastal areas. Availability of fresh water resources across the region is expected to become scarcer, as these climate trends continue and the population continues to grow. \_/
Sahel means boundary in Arabic, and the Sahel forms the southern boundary of the world's largest desert, the Sahara. The Sahel is situated mostly between 14° and 18° N latitude, characterized by scrubby grasslands, getting on average between 14-23 inches (35.658.4 cm) of rain per year. It is home to about 25 million people, most of whom are nomadic herders and subsistence farmers. In the summer months of June and July, heating normally causes air to rise and this is replaced by moist air from the Atlantic, which brings the annual rainfall. The Sahel has experienced the ravages of many fluctuations in climate change events. In 1968, the normal northward movement of the wet intertropical convergence zone stopped during an ENSO event, and further climatic changes in the 1970s led to only about half of the normal rain falling up until 1975. With additional lack of moisture brought on by complications from the temperature cycles of the northern and southern oceans becoming out of synchronicity at this time, the region suffered long-term drought and permanent desertification.
As the rains continued to fail to come and the air masses continued to evaporate surface water, the soil moisture was drastically reduced, which further reduced evaporation and cloud cover. The vegetation soon died off, and the soils became dry and hot and near-surface temperatures were further increased. Soon, the plants were gone, the soils were exposed to the wind, and the region became plagued with blowing dust and sand. Approximately 200,000 people died, and 12 million head of livestock perished. Parts of the region were altered to desert, with little chance of returning to the previous state.
The desertification of the Sahel was enhanced by the agricultural practices of the people of the region. Nomadic and marginal agriculture was strongly dependent on the monsoon, and when the rains did not come for several years, the natural and planted crops died. Many of the remaining plants were used as fuel for fires to offset the cost of fuel. This practice greatly accelerated the desertification process. The Sahara is now thought to be overtaking the Sahel by migrating southward at approximately three miles (5 km) per year.
One of the worst-stricken regions of the Sahel is the Darfur region of the Sudan, where years of drought have exacerbated political and religious unrest. Opposing parties raid Red Cross relief supplies and sabotage the other side's attempts at establishing aid and agriculture, and the people suffer. One of the unpleasant aspects of human nature is that slow-moving, long-lasting disasters like drought tend to bring out the worst in many people. War and corruption often strike drought-plagued regions once relief and foreign aid begins to bring outside food sources into regions. This food may not be enough to feed the whole population, so factions break off and try to take care of their own people. By 1975 about 200,000 people had died, millions of herd animals were dead, and crops and the very structure of society in many Sahel countries was ruined. Children were born brain-damaged because of malnutrition and dehydration, and corruption had set in.
Since the 1980s the region has been plagued with continued more-sporadic drought, but the infrastructure of the region has not returned and the people continue to suffer. Drought led in part to greater civil, ethnic, and religious strife and from 1983-87 the region endured a brutal civil war, when drought drove nomadic Zaghawa and Arab tribes south into ethnic Fur territory. Supply of weaponry and arms to the region increased dramatically, and in 1987 the situation took a political turn for the worse. Twenty-seven nomadic Arab tribes declared an alliance and religious war against the native Zurug (black) and non-Arab tribes of Darfur, who responded by forming their own militias. The Arab tribes were attempting to survive the drought by claiming new land, through killing and driving out whole villages in a campaign of "ethnic cleansing" that has since become one of the world's most horrific examples of genocide. New droughts in 1989, 1990, 1997, 2000, and 2004, continuing to 2008, have caused additional suffering. The Darfur remains parched, and one of the root causes of the civil war and genocide in the region that has by 2008 led to the deaths of hundreds of thousands of people is drought and the slow expansion of the Sahara Desert.
Drought disasters are not limited to sub-Saharan Africa. Soon after the great U.S. stock market crash of October 1929, the central United States farmland suffered one of its worst drought disasters known, plunging the United States into the Great Depression of the 1930s. Changes in the upper level atmospheric circulation patterns caused upper level dry air to sink into the Great Plains region, and as the air sank it became warmer and drier. The air seemed to soak the moisture right out of the ground, and the crops died, exposing the barren soils to the action of the wind. The winds blew across the Plains states, raising huge clouds of dust known as rollers that moved like thousands-of-feet (hundreds-of-m)-tall steam rollers across the plains. This dust permeated everything, filling homes, lungs, eyes, and every available space with the fine-grained airborne plague. The dust storms became so bad they blocked out the sun, moved across East Coast cities, and even hampered shipping in the Atlantic when they covered ships.
Soon people began leaving the plains in the thousands. Many moved west to California, where the land was available but is now overcrowded and plagued with drought. The Plains States were left in a shambles as the dust bowl days continued into the late 1930s. Numerous studies have indicated that much of the disaster could have been prevented. The weather conditions could not have been changed, and the drought would have occurred, but the severity might have been lessened if the farmers in the region knew that the techniques they were using were actually contributing to the disaster. The farmers were digging deeply into the native soils, disrupting the root systems of existing plants, killing drought-resistant plants, and replacing these with higher-yield crops with shallow root systems. When the drought came, these crops died and the bare soil was exposed and was removed by the strong winds. Even though this area had suffered droughts before, it was mostly not farmed at those times, and the drought-resistant plants native to the region were able to prevent the soil from being eroded by the winds. Now, modern farming techniques are employed in the region, and it should be able to sustain another drought similar to the 1930s without such a huge disaster.
drought and Water Shortage Brought on by population Growth
Drought can also be brought on by rapid increases in population, water use (and abuse), and migrations of people into desert or semiarid regions. Although these regions may never have been able to sustain large populations with their indigenous water supplies, settlement of places like Southern California, the U.S. desert Southwest, and the rapid population expansion in the Middle East all offer examples of how drought-like water shortage conditions are experienced by the people living in these regions.
Drought or basic water shortage coupled with rapid population growth provides for extreme volatility for any region, and the Middle East is one of the most volatile regions in the world. In this region, water shortage issues are coupled with long-standing political and religious differences that have often erupted into conflict and war. The Middle East region, which stretches from North Africa and the Arabian Peninsula through the Levant to Turkey and along the Tigris-Euphrates Valley, has only three major river systems and a few smaller rivers. The population stands at close to 200 million people but is growing rapidly. The Nile has an annual discharge of about 82 billion cubic yards (62.7 billion m3), whereas the combined Tigris-Euphrates system has an annual discharge of 93 billion cubic yards (71 billion m3). Some of the most serious water politics and drought issues in the Middle East arise from the four states that share the relatively small amounts of water of the Jordan River, with an annual discharge of less than 2 billion cubic yards (1.5 billion m3). It has been estimated that with current water usage and population growth, many nations in this region have only a decade left before the agriculture and eventual security of these nations will be seriously threatened.
The region is arid, receiving 1-8 inches (2.5-20 cm) of rain per year, and has many drought years with virtually no rain. The Middle East has a population growth rate of about 3.5 percent per year, one of the fastest in the world, and many countries in the region have inefficient agricultural practices that contribute to the growing problem of desertification in the region. Some of the problems include planting of water-intensive crops, common flooding and furrow methods of irrigation, spraying types of irrigation that waste much of the water to evaporation, and poor management of water and crop resources. These growing demands on the limited water supply, coupled with political strife resulting from shared usage of waterways that flow through multiple countries, has set the region up for a major confrontation over water rights. Many of the region's past and present leaders have warned that water issues may be the cause of the next major conflict in the Middle East. In the words of the late King Hussein of Jordan, water issues "could drive nations of the region to war."
Personal water use by individuals is by necessity much less in countries in the Middle East than in the United States or in other Western countries. For instance, in the United States every American has about 11,000 cubic yards (8,410 m3) of freshwater potential to use each year, whereas citizens of Iraq (pre-war) have about 6,000 cubic yards (4,590 m3), Turkey 4,400 cubic yards (3,364 m3), and Syria about 3,000 cubic yards (2,294 m3). Along the Nile, Egyptians have about 1,200 cubic yards (917 m3) available for each citizen. In the Levant, Israelis have a freshwater potential of 500 cubic yards (382 m3) per person per year, and Jordanians have only 280 cubic yards (214 m3) per year.
People in the Middle East have learned to live without as many showers or freshly watered green lawns as in America and to tolerate a higher level of salt in their drinking water.
The river Nile, the second longest river on Earth, forms the main water supply for nine north-African nations, and disputes have grown over how to share this water with growing demands. The Blue Nile flows out of the Ethiopian Highlands and meets the White Nile in the Sudan north of Khartoum, then flows through northern Sudan and into Egypt. The Nile is dammed at Aswan, forming Lake Nasser, then flows north through the fertile valley of Egypt to the Mediterranean. Some of the water has been diverted in a project to make a fertile valley east of Lake Nasser, and additional water is diverted in a canal that runs to Sinai. Numerous dams along the Nile, including the large Aswan High Dam, have stopped much of the silt that used to flow down the river, with one result being that the Nile delta is not receiving the sediment it needs to remain above sea level, and large areas of the delta are disappearing below sea level.
The Nile is the only major river in Egypt, and nearly all of Egypt's population lives in the Nile Valley. About 3 percent of the nation's arable land stretches along the Nile Valley, but 80 percent of Egypt's water use goes to agriculture in the valley. The government has been attempting to improve agricultural and irrigation techniques, which in many places have not changed considerably for 5,000 years. If the Egyptian agricultural community embraced widespread use of drip irrigation and other modern agricultural practices, then the demands on water could easily be reduced by 50 percent or more. In nearby Israel, drip irrigation projects have changed barren desert landscapes into productive farmland.
The Jordan River basin is host to some of the most severe drought and water shortage issues in the Middle East. Israel, Jordan, Syria, Lebanon, and the Palestinians share the Jordan River water, and the resource is much more limited than water along the Nile or in the Tigris-Euphrates system. The Jordan River is short (100 miles [160 km]), and is made of three main tributaries, each with different characteristics. The Has-bani River has a source in the mountains of Lebanon and flows south to Lake Tiberias, and the Banias flows from Syria into the lake. The smaller Dan River flows from Israel. The Jordan River then flows out of Lake Tiberias, is joined by water from the Yarmuk flowing out of Syria, then flows into the Dead Sea, where any unused water evaporates.
The Jordan River is the source for about 60 percent of the water used in Israel and 75 percent of the water used in Jordan. The other water used by these countries is largely from groundwater aquifers. Israel has almost exclusive use of the coastal aquifer along the Mediterranean shore, whereas disputes arise over use of aquifers from the
West Bank and Golan Heights. These areas are mountainous, get more rain and snowfall than the other parts of the region, and have some of the richest groundwater deposits in the region. Since the 1967 war, Israel has tapped the groundwater beneath the West Bank and now gets approximately 30-50 percent of its water supply from groundwa-ter reserves beneath the mountains of the West Bank. The Palestinians get about 80 percent of their water from this mountain aquifer. A similar situation exists for the Golan Heights, though with lower amounts of reserves. These areas therefore have attained a new significance in terms of regional negotiations for peace and land in the region.
The main problems of water use stem from the shortage of water compared to the population, effectively making drought conditions. The situation is not likely to get better given the alarming 3.5 percent annual population growth rate. Conservation efforts have only marginally improved the water use problem, and it is unlikely that there will be widespread rapid adoption of many of the drip-irrigation techniques used in Israel throughout the region. This is partly because it takes a larger initial investment in drip irrigation than in conventional furrow and flooding types of irrigation systems. Many of the farmers can not afford this investment, even if it would improve their long-term yields and decrease their use of water. Even when existing drip irrigation and greenhouse technology and equipment was left behind by Israeli farmers when they evacuated Gaza, the succeeding days saw widespread looting and destruction of the equipment to sell the parts for fast cash. The result was the loss of a productive agricultural area in the desert and a decimated economy.
Sporadic droughts have made this situation worse in recent years, such that in 1999 Israel cut in half the amount of water it supplies to Jordan, and Jordan declared drought conditions and mandated water rationing. Jordan currently uses 73 percent of its water for irrigation, and if this number could be reduced by adoption of more efficient drip-irrigation, the current situation would be largely in control.
One possible way to alleviate the problem of the drought and water shortage would be to explore for water in unconventional aquifer systems such as fractures or faults, which are plentiful in the region. Many faults are porous and permeable structures that are 30-40 feet (several tens of m) wide and miles (thousands of m) long and deep. They may be thought of as vertical aquifers, holding as much water as conventional aquifers. If these countries were to successfully explore for and exploit water in these structures, the water shortage and regional tensions might be reduced. This technique has proven effective in many other places in the Middle East, Africa, and elsewhere and would probably work here as well. One exploration strategy used by several independent teams is to map the faults and fractures using satellite imagery and do some further analysis in the field and computer modeling to determine which fracture systems might be more likely to yield significant groundwater resources.
A different set of problems plagues the Tigris-Euphrates drainage basin and the countries that share water along their course. There are many political differences between the countries of Turkey, Syria, and Iraq, and the Kurdish people have been fighting for an independent homeland in this region for more than a decade. One of the underlying causes of dispute in this region is also the scarce water supply in a drought-plagued area. Turkey is in the midst of a massive dam construction campaign, with the largest dam being the Attaturk on the Euphrates. Overall, Turkey is spending an estimated 32 billion dollars on 22 dams and 19 hydroelectric plants. The aim is to increase the irrigated land in Turkey by 40 percent and to supply 25 percent of the nation's electricity through the hydroelectric plants. This system of dams also now allows Turkey to control the flow of the Tigris and the Euphrates, and if it pleases, Turkey can virtually shut off the water supply to its downstream neighbors. At present Turkey is supplying Syria and Iraq with what it considers to be a reasonable amount of water, but what Syria and Iraq claim is inadequate. Turkey is currently building a pipeline to bring water to drought-stricken Cyprus. Turkey and Israel are forging new partnerships and have been exploring ways to export water from Turkey and import it to Israel, which could help the drought in the Levant.
The history of development the U.S. desert Southwest was also crucially dependent on bringing water resources into this semi-arid region. Much of California was regarded as worthless desert scrub land until huge water projects designed by the Bureau of Land Reclamation diverted rivers and resources from all over the west. Development of the U.S. desert Southwest involves a long history of controversy and corruption associated with the diversion of water resources from Owens Valley, the Trinity River, the Colorado River, and many other western sources and has many parallels to ill-fated societies elsewhere in the history of the world. Now, much of the region has reached a population density that has exceeded the amount of water available to feed the population, and some of the agricultural areas are experiencing increasing saltiness of the soils from evaporation of irrigation waters. The region could become even drier and hotter as the global climate warms, creating a drought crisis that may require people to leave the region.
Shifting Deserts and Desertification
Deserts expand and contract, reflecting global environmental changes. Many cultures and civilizations on the planet are thought to have met their demise because of desertification of the lands they inhabit and their inability to move with the shifting climate zones. Desertification is defined as the degradation of formerly productive land, and it is a complex process involving many causes. Climates may change, and land use on desert fringes may make fragile ecosystems more susceptible to becoming desert. Among civilizations thought to have been lost to the sands of encroaching deserts are several Indian cultures of the American Southwest such as the Anasazi and many peoples of the Sahel, where up to 250,000 people are thought to have perished in droughts in the late 1960s. Expanding deserts are associated with shifts in other global climate belts, and these shifts too are thought to have brought down several societies. Included are the Mycenaean civilization of Greece and Crete, the Mill Creek Indians of North America, and perhaps even the Viking colony in Greenland. Many deserts are presently expanding, creating enormous drought and famine conditions like those in Ethiopia and Sudan.
Desertification is the invasion of a desert into non-desert areas and is an increasing problem in the southwestern United States, in part due to human activities. This decreases water supply, vegetation, and land productivity; about 10 percent of the land in this country has been converted to desert in the last 100 years, while nearly 40 percent is well on the way. Desertification is also a major global problem, costing hundreds of billions of dollars per year. China estimates that the Gobi Desert alone is expanding at a rate of 950 square miles per year (2,460 km2), an alarming increase since the 1950s when the desert was expanding at less than 400 square miles (1,036 km2) per year. The expansion of the Gobi is estimated to cost 6.7 billion dollars a year in China and affects the livelihood of more than 400 million people.
Desertification is a global problem, which could drastically alter the distribution of agriculture and wealth on the globe as the global climate
changes. Many deserts are predicted to continue to expand, including the wheat belt of the central United States that will be displaced to Canada. The sub-Saharan Sahel will become part of the Sahara, and the Gobi Desert may expand out of the Alashan and Mongolian Plateaus into northeastern China.
Desertification is a multistage process, beginning with drought, crop and vegetation loss, and then establishment of a desert landscape like those described above. Drought alone does not cause desertification, but misuse of the land during drought greatly increases the chances of a stressed ecosystem reverting to desert. Desertification is associated with a number of other symptoms, including destruction of native and planted vegetation, accelerated and high rates of soil erosion, reduction of surface and groundwater resources, increased saltiness of remaining water supplies, and famine. Desertification can be accelerated by human-induced water use, population growth, and settlement in areas that do not have the water resources to sustain the exogenous population.
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