Part 3

It is a misconception that droughts cause desertification. Droughts are common in arid and semiarid lands. Well-managed lands can recover from drought when the rains return. Continued land abuse during droughts, however, increases land degradation. By 1973, the drought that began in 1968 in the Sahel of West Africa and the land-use practices there had caused the deaths of more than 100,000 people and 12 million cattle, as well as the disruption of social organizations from villages to the national level.

While desertification has received tremendous publicity by the political and news media, there are still many things that we don’t know about the degradation of productive lands and the expansion of deserts. In 1988 Ridley Nelson pointed out in an important scientific paper that the desertification problem and processes are not clearly defined. There is no consensus among researchers as to the specific causes, extent, or degree of desertification. Contrary to many popular reports, desertification is actually a subtle and complex process of deterioration that may often be reversible.

Global monitoring

In the last 25 years, satellites have begun to provide the global monitoring necessary for improving our understanding of desertification. Landsat images of the same area, taken several years apart but during the same point in the growing season, may indicate changes in the susceptibility of land to desertification. Studies using Landsat data help demonstrate the impact of people and animals on the Earth. However, other types of remote-sensing systems, land-monitoring networks, and global data bases of field observations are needed before the process and problems of desertification will be completely understood.

Local remedies

At the local level, individuals and governments can help to reclaim and protect their lands. In areas of sand dunes, covering the dunes with large boulders or petroleum will interrupt the wind regime near the face of the dunes and prevent the sand from moving. Sand fences are used throughout the Middle East and the United States, in the same way snow fences are used in the north. Placement of straw grids, each up to a square meter in area, will also decrease the surface wind velocity. Shrubs and trees planted within the grids are protected by the straw until they take root. In areas where some water is available for irrigation, shrubs planted on the lower one-third of a dune’s windward side will stabilize the dune. This vegetation decreases the wind velocity near the base of the dune and prevents much of the sand from moving. Higher velocity winds at the top of the dune level it off and trees can be planted atop these flattened surfaces.

Oases and farmlands in windy regions can be protected by planting tree fences or grass belts. Sand that manages to pass through the grass belts can be caught in strips of trees planted as wind breaks 50 to 100 meters apart adjacent to the belts. Small plots of trees may also be scattered inside oases to stabilize the area. On a much larger scale, a “Green Wall,” which will eventually stretch more than 5,700 kilometers in length, much longer than the famous Great Wall, is being planted in northeastern China to protect “sandy lands”—deserts believed to have been created by human activity.

More efficient use of existing water resources and control of salinization are other effective tools for improving arid lands. New ways are being sought to use surface-water resources such as rain water harvesting or irrigating with seasonal runoff from adjacent highlands. New ways are also being sought to find and tap groundwater resources and to develop more effective ways of irrigating arid and semiarid lands. Research on the reclamation of deserts also is focusing on discovering proper crop rotation to protect the fragile soil, on understanding how sand-fixing plants can be adapted to local environments, and on how grazing lands and water resources can be developed effectively without being overused.

If we are to stop and reverse the degradation of arid and semiarid lands, we must understand how and why the rates of climate change, population growth, and food production adversely affect these environments. The most effective intervention can come only from the wise use of the best earth-science information available.

Selected Readings

Bagnold, R. A., 1941, The physics of blown sand and desert dunes: Methuen, London, 265 p. (A classic treatise concerning the origin and evolution of dunes.)

Breed, C. S., and others, 1979, Regional studies of sand seas, using Landsat (ERTS) imagery: _in_ McKee, E. D., ed., A study of global sand seas: U.S. Geological Survey Professional Paper 1052, p. 305-397. (A study of selected sand seas based on analysis of remote sensing images, surface wind summaries, and available literature.)

Cook, R. U., and Warren, Andrew, 1973, Geomorphology in deserts: University of California Press, Berkeley, California, 374 p. (Examines the nature of landforms, soils, and geomorphological processes in the world’s deserts.)

Eigeland, Tor, and others, 1982, The desert realm: National Geographic Society, Washington, 304 p. (A well illustrated discussion of deserts of America, Africa, Asia, and Australia.)

Ericksen, G. E., 1983, The Chilean nitrate deposits: American Scientist, v. 71, p. 366-374. (A discussion of the origin of the Chilean nitrate deposits which has puzzled scientists for more than 100 years.)

Gerster, Georg, 1960, Sahara-desert of destiny: Coward-McCann, New York, 302 p. (How plants, animals, and people survive in the Sahara.)

Greeley, Ronald, and Iversen, J. D., 1985, Wind as a geological process on Earth, Mars, Venus and Titan: Cambridge University Press, New York, 333 p. (Expands the classic work of Bagnold to discuss eolian processes in a planetary context. Describes the processes on all moons and terrestrial planets with atmospheres.)

Hare, F. K., 1983, Climate on the desert fringe: _in_ Gardner, Ritz, and Scoging, Helen, eds., Mega-geomorphology: Clarendon Press, Oxford, p. 134-151. (The margins of many deserts are affected by tension between society and environment. This paper summarizes the climatology of arid zones.)

MacMahon, James A., 1985, Deserts: Alfred A. Knopf, Inc., New York, 640 p. (An Audubon Society Nature Guide to the deserts of the United States, and their inhabitants.)

McCauley, J. F., and others, 1984, Remote monitoring of processes that shape desert surfaces: The Desert Winds Project: U.S. Geological Survey Bulletin 1634, 19 p. (Describes a new study on collecting weather data from solar-powered data-collection platforms in deserts. The data are relayed by a GOES satellite to the USGS in Flagstaff, Arizona, and converted to graphic form.)

Meigs, Peveril, 1953, World distribution of arid and semi-arid homoclimates: _in_ Reviews of research on arid zone hydrology: Paris, United Nations Educational, Scientific, and Cultural Organization, Arid Zone Programme-1, p. 203-209. (Classifies arid lands according to precipitation.)

Nelson, R., 1988, Dryland management: the desertification problem: Environmental Department Working Paper No. 8, Washington: World Bank, 42 p. (An excellent review of the present state of knowledge concerning desertification.)

Tolba, M. K., 1984, Desertification is stoppable: Arid Lands Newsletter No. 21, p. 2-9. (A discussion of the problems involved in preventing desertification and reclaiming arid lands.)

Walker, A.S., 1986, Eolian geomorphology: _in_ Short, N.M., and Blair, R.W., eds., Geomorphology from space: a global overview of regional landforms: NASA SP-486, p. 447-520 (a brief review of desert processes).

Warren, A. and Agnew, C., 1988, An assessment of desertification and land degradation in arid and semi-arid areas: International Institute for Environment and Development, Drylands Programme, Paper 2, London: IIED, 103 p. (An evaluation of land degradation problems.)

The metric units used in this publication can be converted to English units by using the approximate conversions given below:

Length

1 kilometer 0.6 of a mile 1 meter 39.37 inches 1 centimeter 0.4 inch 1 millimeter 0.04 inch

Area

1 sq. kilometer 0.04 sq. mile 1 sq. meter 1.2 sq. yards 1 sq. centimeter 0.155 sq. inch

Temperature

To convert °Celsius to °Fahrenheit, multiply °C by 1.8 and add 32. To convert °Fahrenheit to °Celsius, subtract 32 from °F and divide the result by 1.8.

_In this desert there are a great many evil spirits and also hot winds; those who encounter them perish to a man. There are neither birds above nor beasts below. Gazing on all sides as far as the eye can reach in order to mark the track, no guidance is to be obtained save from the rotting bones of dead men, which point the way._

_Explorer Fa Xian describing the Taklimakan Desert of China about 400 A.D._

This publication is one of a series of general interest publications prepared by the U.S. Geological Survey to provide information about the earth sciences, natural resources, and the environment. To obtain a catalog of additional titles in the series “General Interest Publications of the U.S. Geological Survey,” write:

U.S. Geological Survey Branch of Distribution P.O. Box 25286 Denver, CO 80225

★ U. S. GOVERNMENT PRINTING OFFICE : 1992 0-332-326 QL 2

As the Nation's principal conservation agency, the Department of the Interior has responsibility for most of our nationally-owned public lands and natural and cultural resources. This includes fostering wise use of our land and water resources, protecting our fish and wildlife, preserving the environmental and cultural values of our national parks and historical places, and providing for the enjoyment of life through outdoor recreation. The Department assesses our energy and mineral resources and works to assure that their development is in the best interests of all our people. The Department also promotes the goals of the Take Pride in America campaign by encouraging stewardship and citizen responsibility for the public land and promoting citizen participation in their care. The Department also has a major responsibility for American Indian reservation communities and for people who live in Island Territories under U.S. Administration.

Cover Photographs:

Transcriber’s Notes

--Corrected a few typographical errors.

--Slightly displaced photographs and captions for better display on scrolling eBook viewers.