The intensive rainfall is considered an important factor of the transport of pathogenic micro-organism, including malaria parasites. Conversely, drought caused by the drop of annual rainfall over a 30-year interval was associated with the decrease of parasite index in children in Senegal, Africa (Faye, 1995 cited in Hong, 1998). So it is clear that the duration of rainy and dry seasons and the interval of those seasons affect larvae and adult vector development and abundance (Patz, 2000).
The difference between malaria patterns at District level and at the village level may be due to many factors. Firstly, :malaria was distributed unevenly within the villages. Secondly, the data points that were collected in health center were insufficient to give a complete description of malaria prevalence in the villages. Thirdly, malaria is influenced by local specific conditions. However, in this district, the areas of endemic malaria are very wide with much variability. Thus, it was very difficult to have a clear pattern of malaria transmission without a good monitoring system. In Africa, the scarcity of basic data and the lack of understanding malaria situation is one of the enormous problems in malaria control program (MARA, 2001).