Senegal occupies 196,722 square kilometers on the westernmost bulge of the African continent. The country sits between 12° and 17° north latitude and 11° and 18° west longitude. Mauritania borders the north, Mali the east, and Guinea and Guinea-Bissau the south. The Atlantic Ocean forms the entire western boundary extending roughly 530 kilometers. The Gambia, a separate nation, creates a narrow eastward intrusion into Senegalese territory, following the Gambia River valley for approximately 350 kilometers and splitting the country's southern Casamance region from the rest of Senegal.
Cap-Vert, located on the peninsula extending from Dakar, marks the westernmost point of continental Africa at 17.5° west longitude. This peninsula juts approximately 15 kilometers into the Atlantic and reaches elevations near 100 meters at its volcanic outcrops, though most terrain sits below 50 meters. The Cape Verde Peninsula formed from volcanic activity in the Quaternary period, distinguishing it geologically from the sedimentary plains that characterize most of Senegal. The peninsula's position creates microclimates in Dakar that differ measurably from areas 20 kilometers inland.
Three major river systems drain Senegal. The Senegal River originates in Guinea's Fouta Djallon highlands, flows 1,790 kilometers, and forms the entire northern border with Mauritania before reaching the Atlantic at Saint-Louis. The Diama Dam, completed in 1986 at 27 kilometers from the river mouth, prevents saltwater intrusion upstream and enables year-round irrigation across 375,000 hectares in the river valley. The Gambia River enters Senegal from Guinea, crosses the southeastern region through Tambacounda, then flows through The Gambia nation entirely before reaching the ocean. The Casamance River drains the southern region, running 300 kilometers westward from Guinea-Bissau border hills to reach the Atlantic near Ziguinchor, creating extensive mangrove estuaries where freshwater meets tidal saltwater.
The Saloum River and its tributaries create the Sine-Saloum Delta, where 72,000 hectares of mangrove forests, tidal channels, and over 200 islands form an ecosystem recognized as a UNESCO Biosphere Reserve in 1980. This delta system extends approximately 150 kilometers inland from the Atlantic coast between Dakar and The Gambia. Tidal influence reaches 100 kilometers upstream during dry season low-flow conditions. Salt concentrations in delta channels vary from 35 parts per thousand at the ocean interface to under 10 parts per thousand at inland limits during rainy season peak flow.
Senegal's topography remains predominantly flat. Approximately 85 percent of the country sits below 100 meters elevation. The highest point reaches 581 meters at an unnamed location in the Fouta Djallon foothills near the southeastern Guinea border in Kédougou region. The Niayes region extends along the coast from Dakar north to Saint-Louis as a narrow strip of fossil sand dunes, some reaching 20 to 30 meters height, with inter-dunal depressions lying at or below sea level where freshwater tables support intensive market gardening. These depressions typically measure 200 to 800 meters wide and extend several kilometers parallel to the coastline.
The Ferlo Desert occupies the north-central interior between the Senegal River valley and the groundnut basin near Kaolack. This semi-arid zone receives 300 to 500 millimeters of annual rainfall concentrated in three months, supports scattered acacia and baobab trees at densities of 5 to 20 per hectare, and experiences surface water availability only during July through October. Daytime temperatures in the Ferlo reach 40 to 45 degrees Celsius from April through June. Pastoral communities historically migrated through this region seasonally, moving livestock to the Senegal River valley during the nine-month dry period when temporary pools disappeared.
Lake Retba, located 35 kilometers northeast of Dakar, covers approximately 3 square kilometers and reaches maximum depths near 3 meters. The lake has no surface outlet to the ocean located 500 meters west across a sand barrier. Evaporation concentrates salinity to 380 grams per liter, ten times ocean levels and comparable to the Dead Sea's 340 grams per liter. Dunaliella salina algae produce pink-red carotenoid pigments visible when afternoon sunlight penetrates the water, creating the pink appearance that gives the lake its Lac Rose nickname. Salt harvesting removes approximately 50,000 tons annually from lake-bottom deposits that reach 1 meter thickness in areas where extraction has not occurred.
Senegal experiences three distinct seasons driven by the West African monsoon system. The rainy season runs from June through October as the Intertropical Convergence Zone shifts northward, bringing moist Atlantic air masses inland. Dakar receives 500 to 600 millimeters annually over 35 to 45 rain days. Saint-Louis in the northern Sahel zone receives 200 to 300 millimeters over 25 to 35 rain days. Ziguinchor in the southern Casamance region receives 1,200 to 1,500 millimeters over 70 to 90 rain days. The intensity and duration gradient from north to south determines vegetation patterns, with Guinea savanna woodlands in Casamance grading northward through Sudan savanna to Sahel thornbush.
The hot dry season extends from March through May before the monsoon onset. Continental air masses from the Sahara dominate, pushing daytime temperatures to 35 to 40 degrees Celsius across most regions. Dakar reaches 28 to 32 degrees Celsius during this period due to Atlantic influence. Relative humidity drops below 30 percent away from the coast. This season marks the agricultural preparation period when farmers clear fields and repair equipment before the rains begin. Rivers reach their lowest flows, with the Senegal River at Saint-Louis dropping to 10 to 20 cubic meters per second compared to rainy season peaks of 2,000 to 3,000 cubic meters per second.
The cool dry season runs from November through February when the Harmattan wind system brings continental air from the northeast. Dakar temperatures range from 18 to 26 degrees Celsius. Interior regions experience wider diurnal ranges, with morning lows of 12 to 16 degrees Celsius and afternoon highs of 28 to 34 degrees Celsius. The Harmattan carries fine dust particles from Saharan sources, reducing visibility to 1 to 3 kilometers on heavy dust days and creating a dry haze that limits solar radiation reaching the surface. Atlantic influence moderates these conditions within 50 kilometers of the coast, where sea breezes develop most afternoons.
Dakar's Atlantic peninsula location creates microclimates distinct from interior regions 100 kilometers east. Mean annual temperature in Dakar reaches 24.5 degrees Celsius with a narrow range from 21 degrees in January to 28 degrees in September. Interior locations like Tambacounda average 28.5 degrees Celsius annually, ranging from 24 degrees in December to 33 degrees in May. Nighttime temperatures in Dakar rarely drop below 18 degrees Celsius year-round, while Tambacounda experiences lows of 12 to 14 degrees Celsius during December and January. This Atlantic moderation allows continuous vegetable cultivation in Dakar's Niayes region while interior agriculture remains limited to the rainy season.
Rainfall variability creates periodic drought conditions. The 1968-1985 Sahel drought reduced Senegal's average rainfall by 20 to 30 percent compared to 1920-1960 means. Dakar's long-term average near 550 millimeters dropped to 350 to 450 millimeters during 1970-1985. Agricultural yields declined proportionally, forcing rural-urban migration that increased Dakar's population from 400,000 in 1960 to over 1 million by 1985. Rainfall patterns since 1990 show partial recovery, with Dakar averaging 500 to 520 millimeters from 1990 to 2020, though year-to-year variability remains high with individual years ranging from 300 to 800 millimeters.