Int. J. Environ. Res. Public Health 2010, 7 1713 This shift of tsetse toward the south has therefore been a general process since the beginning of the 20th century that can be partly attributed to these drought episodes. The main result of these drought episodes is the shift of isohyets to the south by 50–200 km depending on the longitude, to which is superimposed the shift of northern tsetse flies limit (Figure 2). The impact of the 1970s drought episodes on tsetse distribution in Burkina Faso has been described in [32]. In the same period, the population of Burkina Faso has undergone a spectacular increase. From 2.8 million inhabitants in 1910 (density 10/km2), the population reached 13.9 million in 2005 (51/km2) [33,34]. This increase in population density, varying by region, has had a strong impact on vegetation because of the extension of cultivated areas. In Burkina Faso, the Mossi territory located in a quadrilateral within the Ouahigouya-Manga-Tenkodogo-Kaya perimeter surrounding Ouagadougou, is historically known for its high density [35,36] (Figure 2). Figure 2. North to south shift of tsetse and rainfall, and settlement changes over time in Burkina Faso. This map shows the country of Burkina Faso with its different climatic areas and the changes in isohyets distribution between 1931 and 1989. It illustrates the north-south shift in isohyets distribution, and the variable north-south shift of the northern tsetse limit. In this territory, the population density can reach more than 100/km2, and the landscape has been dramatically modified, due to the extension of agriculture, including degradation of gallery forests along rivers (Figure 3), in the same area where the northern tsetse limit has shifted the most toward the south since 1977.