Why do some rivers in Burkina Faso become dry during the dry season?

Rivers in Burkina Faso experience significant seasonal flow variations due to the country's climate, which is characterized by distinct wet and dry seasons.12

The primary reason some rivers become dry beds during the dry season is the limited and erratic nature of rainfall. Burkina Faso experiences a rainy season that lasts only from June to September, while the remainder of the year is dominated by dry conditions. In the northern Sahelian zone, rainfall is particularly scarce, often lasting only three to five months.1

During the hot season, which lasts from mid-February to June, temperatures can rise into the low 100s °F (about 40 °C) in the shade. This heat, combined with the prevalence of the harmattan—a hot, dry, dust-laden wind blowing from the Sahara—increases evaporation rates. Consequently, the lack of consistent precipitation and high evaporation levels cause many watercourses to dry up completely outside of the brief rainy period.12