Burkina Faso is a landlocked country located in the in the middle of West Africa's "hump." It is geographically in the Sahel--the agricultural region between the Sahara Desert and the coastal rain forests. Most of central Burkina Faso lies on a savanna plateau, 200 meters-300 meters (650 ft.-1,000 ft.) above sea level, with fields, brush, and scattered trees. The largest river is the Mouhoun (Black Volta), which is partially navigable by small craft. Burkina Faso has West Africa's largest elephant population. Game preserves also are home to lions, hippos, monkeys, warthogs, and antelope. Infrastructure and tourism are, however, not well developed. Annual average rainfall varies from about 100 centimeters (40 in.) in the south to less than 25 centimeters (10 in.) in the north and northeast, where hot desert winds accentuate the dryness of the region. The cooler season, November to February, is pleasantly warm and dry (but dusty), with cool evenings. March-June can be very hot. In July-September, the rains bring a 3-month cooler and greener humid season.