Introduction

The Mediterranean climate of North Africa is characterized by hot dry summers and seasonally restricted rainfall. The western region experiences a subhumid Mediterranean climate with mild, moist winters from October through March/April, and hot, dry summers from May through September. Nevertheless, the climate is quite variable from year to year, and the North Atlantic oscillation has a large interan-nual influence on winter rainfall patterns, particularly in Morocco. The Saharan mountain chains running northeast also have a major influence on rainfall, and in Morocco the Atlas Mountains can receive an annual rain fall of over 200 cm. The Atlantic influence on rainfall diminishes eastwards, although mountains in northwest Tunisia can receive over 150 cm of the annual rainfall. Further to the east, across the northern parts of Libya and Egypt, rainfall <10 cm is received annually. The temporal and spatial distribution of rainfall in North Africa has important consequences for inland waters. Irregular rainfall from year to year and high evapotranspiration rates combined with an essentially unglaciated geology favor a diversity of standing water types, with a bias toward shallow ephemeral water bodies in lowland regions. Run-off is collected by a variety of depressions that range from small transitory ponds (often salinized in summer months) to permanent natural and predominantly freshwater lakes, which are sometimes of large dimension. Of the larger natural freshwater lakes, exceeding 1 km2, most are restricted to Morocco and Algeria and the Nile delta region of Egypt, although substantial coastal lagoons are common in all the countries bordering the southern Mediterranean. There are several common local terms used to categorize North African lakes (including daya and chott) and use of these has become current practice by limnolo-gists and hydrologists, beyond the southern Mediterranean region, especially in Mediterranean Europe.

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