Precipitation

[[image:rainfall.JPG align="right"]]Precipitation
Precipitation affects human society in several ways. Adequate rainfall is vital to agriculture, particularly in places engaged in rainfed agriculture because irrigation is too expensive or infeasible. Yet while a certain amount of average rainfall is important, the variability in rainfall can wipe out an entire harvest either by limiting water available to plants during key parts of their development, or, on the other extreme, flooding fields and ruining crops. The growth of the human population has pushed groups of people into ever more precarious situations with regards to agriculture. In the Sahel of Sub-Saharan Africa, for example, farmers can barely eke out crops from the semiarid landscape, and years with poor rainfall relative to the average results in mass malnutrition and death. To make matters worse, long-term climate change is shifting precipitation patterns around the world. In the case of the Sahel, there has been a noticable downward trend in rainfall, as shown on the graphic above. Without investments in infrastructure and an African Green Revolution, the prospects for agriculture in the Sahel seem increasingly grim.

Outside of agriculture, precipitation can affect health directly. Water-borne diseases such as cholera can worsen when there is flooding. In addition, the life cycle of several infectious diseases can often depend on available pools of water. For example, the anopheles mosquito that transmits malaria goes through a larval cycle that requires ponds of still water or other small water bodies. This is true of dengue, yellow fever, and African sleeping sickness (all transmitted by mosquitos); schistosomiasis (transmitted through freshwater snails); and hookworm (parasitic nematodes living in very moist soil).

In the MV Sim, the level of precipitation in a given season affects the maize and cotton yields, although the pernicious effects of a severe drought can be mitigated by investing in irrigation. In addition, high levels of precipitation increase the likelihood of a malaria epidemic breaking out.