The climate in the Lake Chad basin is of tropical type in the South to hyper-arid type in the North, whereby the majority of areas in the Lake Chad basin fall into the arid and the semi-arid type. Thus, the climate in the Lake Chad basin can be distinguished in four different climate zones (the Saharan climate, the Sahelo climate, the Sahelo-Sudanian climate and the Sudanian-Guinean climate) with different rainfall levels. The monsoon rains decrease as one moves from the south with 1,500 mm per year to the north with 100 mm per year. Rainfall patterns are influenced by the movement of air masses and therefore determined by the migration of the Intertropical Convergence Zone (ITCZ). They have a direct impact on river flow and, consequently, on the size of Lake Chad. The climate of the Lake Chad area is Sahelian, which is characterised by a very short rainy season from June to October with average precipitation of around 300 mm (1950-2007 in Diffa, Niger) and a long dry season for the rest of the year.