Sahelian Mauritania is a region of Mauritania.
This semi-arid region extends south of Saharan Mauritania to of the Senegal River Valley on the borders with Senegal and Mali. Before the droughts of the 1960s, 1970s, and 1980s, the relatively lush Senegal River valley ranged from sixteen to thirty kilometres north of the river. By the late 1980s, desertification had reached the northern bank of the river in some parts of the valley. Almost all of the valley's economically active population engages in sedentary agriculture or fishing along the Senegal River and its main tributaries—the Karakoro, the Gorgol, and the Garfa. This area supplies most of the country's agricultural production.
The hivernage begins earlier here than in Saharan Mauritania, often lasting from June until October. Because farmers and herders depend on annual rains, a delay of one month in the beginning of the rainy season can cause large losses and lead to mass migrations into Mali. Although temperature extremes are narrower than in the Saharan region, daily variations range from 16°C to 21°C. The harmattan is the prevailing wind. Rainfall in the Senegal River Valley area is higher than in other regions, ranging from 400-600 mm annually, usually between May and September.