Introduction

The northwest African countries of Morocco, Algeria, and Tunisia frequently experience drought*. This region, commonly called the Maghreb, is situated between the Mediterranean and the Sahara Desert on the southern margins of midlatitude storm systems. As a result, both the timing and total amounts of rainfall are extremely irregular. Precipitation levels are generally insufficient for reliable or prosperous rain-fed agriculture in most of the region. Reduced rainfall is caused, among other factors, by the cold Canary Current off the region's western shores, which induces atmospheric stability and decreases the potential for rainfall. High-pressure ridges periodically develop offshore during the autumn-spring rainy season, barring access to moisture-bearing storms. If these high-pressure ridges persist for extended periods, drought results.

Drought is the leading natural hazard in the region and occurs frequently in all three countries. For example, during the twentieth century, Morocco has averaged 1 year of agricultural drought every 3 to 4 years. Unfortunately, there is no detectable periodicity. Each of these Maghreb countries experiences roughly the same frequency of drought. However, drought in one country is often not correlated with drought in the other two countries. For example, in 1988, Morocco had the largest cereal harvest in its entire history (a record since surpassed) while Tunisia suffered its worst harvest in over 40 years owing to drought.

""'Drought" as used here refers primarily to agricultural drought and is assessed through the use of cereal production statistics. This research was supported, in part, by grants from the Human Dimensions of Global Change initiative of the National Science Foundation and the Program in Science and Technology Cooperation of the U.S. Agency for International Development.

Handbook of Weather, Climate, and Water: Atmospheric Chemistry, Hydrology, and Societal Impacts, Edited by Thomas D, Potter and Bradley R. Colman. ISBN 0-471-21489-2 © 2003 John Wiley & Sons, Inc.

Drought has major socioeconomic significance in northwest Africa because rain-fed (nonirrigated) cereal cultivation occupies a predominant place in the region's agriculture. Since pre-Roman times, this region has specialized in production of cereal crops, mainly wheat and barley, though maize and other cereals (including oats, sorghum, millet, rye, and rice) are also cultivated. Cereal crops account for approximately 85% of the region's cropland and are primarily produced by rain-fed methods. Wheat and barley are the mainstays of the national diets in the region and are consumed primarily as bread and cous cous.

Drought in this region sharply reduces both cereal acreage and yields, causing total production to plummet. This poses a food security threat, particularly if drought continues through a second year. Typically, during a drought year, food shortages develop, cereal imports rise dramatically, herds perish or are slaughtered for lack of forage, many farmers temporarily abandon their land and migrate to the cities, and soil erosion and desertification increase. Finally, the affected country's economy suffers a recession.

Good cereal harvests in northwest Africa require adequate rainfall during both the planting season (normally from October to December) and subsequent growing season (which extends until harvesting between April and June, depending on the region). Poor harvests or crop failure can result from rainfall shortages during either season. Given the potential for extreme interannual variability in precipitation levels, 400 mm annual average precipitation is normally considered the threshold for viable rain-fed cereal production in northwest Africa (Bencherifa, 1988b). However, the temporal distribution of rainfall is just as critical as the total amount. For example, if the entire winter precipitation falls during a few intense cloudbursts, most will disappear as runoff and be unavailable for crop use. Thus, regardless of the total amount of rain, drought conditions will probably develop.

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