Morocco Morocco. Encyclopædia Britannica, Inc. Rabat, Morocco

Drainage

Morocco’s mountains capture significant amounts of rain and snow on their windward slopes from storms coming in off the North Atlantic and give rise to numerous perennial watercourses. Indeed, the country has the most-extensive stream network in North Africa. Most streams arise either on the western slopes of the Atlas Mountains or on the southern slopes of the Rif Mountains and flow westward to the Atlantic Ocean. The Sebou is some 280 miles (450 km) long and has the largest volume of any Moroccan river. With its tributaries, the Sebou accounts for almost half of Morocco’s surface water resources. The Drâa, which rises in the High Atlas at the confluence of the Dadès and the Imini, is Morocco’s longest river, approximately 685 miles (1,100 km) in length; all but the headstreams and upper course are usually dry. At 345 miles (555 km) long, the Oum el-Rbia is another significant river, flowing from the Middle Atlas to the Atlantic. The Moulouya is the only major river flowing to the Mediterranean Sea; it originates on the eastern slopes of the Middle Atlas and flows about 320 miles (515 km) to its mouth, which lies near the Algerian frontier. The northern slopes of the Rif are drained by several short streams that also empty into the Mediterranean. Several minor streams originate on the dry eastern slopes of the High Atlas and flow into the Sahara; these include the Guir, the Rheris, and the Ziz. Although their volume is small, they have cut deep gorges. Since the 1930s Morocco’s streams have progressively been dammed for irrigation, hydroelectricity, and flood control.

Soils

A dark clay-marl soil known as tirs, which is found on the Chaouïa, Doukkala, and Abda plains, produces good yields of wheat and barley when precipitation is sufficient and can retain enough moisture to support summer pasture. Hamri, a light reddish siliceous soil found throughout the Saïs Plain surrounding Meknès and Fès, supports productive vineyards and can also produce good cereal yields, though it has poor moisture retention. Dhess is the main soil type of the Sebou basin. A silt-rich alluvial soil, it provides the foundation for much of Morocco’s modern irrigated agriculture. Other major soil types, less suitable for agriculture, are rmel, a sandy soil found in the Mamora Forest region east of Rabat and along much of the northern coast, and haroucha, a rocky soil found throughout Morocco’s semiarid regions.

Climate

Most of Morocco north of the Western Sahara, particularly along the coasts, experiences a typical Mediterranean climate, with mild wet winters and hot dry summers. The rainy season generally extends from October to April. Torrential downpours occasionally produce devastating floods, but overall several factors act to reduce the country’s rainfall. Morocco is on the southern margins of the mid-latitude tract of frontal storm systems that regularly traverse the North Atlantic. As a result, rainfall levels are relatively low and gradually decrease from north to south. High-pressure ridges, moreover, periodically develop offshore during the rainy season, shifting storms to the north. Drought results when these ridges persist for extended periods. The cold Canary Current off the western shores also induces atmospheric stability and further decreases the potential for precipitation.

In the broad coastal lowlands, average annual precipitation diminishes progressively from about 32 inches (800 mm) on the northern Gharb plain to less than 8 inches (200 mm) in the Sous valley. Farther south, beyond the Anti-Atlas, semiarid conditions quickly fade into desert. Elevation strongly influences this prevailing pattern, however, with significantly greater amounts of precipitation occurring in the mountains. The central Rif, for example, receives more than 80 inches (2,030 mm) of precipitation annually, and even the High Atlas, much farther south, receives some 30 inches (760 mm). Snow is common at approximately 6,500 feet (2,000 metres), and the snowpack lingers in the highest elevations until late spring or early summer. Morocco’s mountains create a significant rain shadow, directly east of the mountains, where in the lee of the prevailing winds, desert conditions begin abruptly.
In the lowlands near the coast, summer heat is reduced by cool onshore breezes. Average daily summer temperatures in the coastal cities range from 64 to 82 °F (18 to 28 °C). In the interior, however, daily highs frequently exceed 95 °F (35 °C). In late spring or summer, the sharqī (chergui)—a hot, dusty wind from the Sahara—can sweep over the mountains into the lowlands, even penetrating the coastal cities. Temperatures rise dramatically, often reaching 105 °F (41 °C). If crops have not been harvested, damage can be extensive from the desiccating effects of the sharqī. In winter the marine influence again moderates temperatures in the coastal regions. Average daily winter temperatures range from 46 to 63 °F (8 to 17 °C). Away from the coast, temperatures drop significantly, occasionally dipping below the freezing point.