Rainwater harvesting in the Sahel

Rainwater harvesting in the Sahel is a combination of "indigenous and innovative" agricultural strategies that "plant the rain" and reduce evaporation, so that crops have access to soil moisture for the longest possible period of time. In the resource-poor drylands of the Sahel region of Africa, irrigation systems and chemical fertilizers are often prohibitively expensive and thus uncommon: so increasing or maintaining crop yields in the face of climate change depends on augmenting the region's extant rainfed agriculture systems to "increase water storage within the soil and replenish soil nutrients." Rainwater harvesting is a form of agricultural water management. Rainwater harvesting is most effective when combined with systems for soil regeneration and organic-matter management. The Sahel is an ecologically (rather than geopolitically) defined region of Africa. The noun Sahel comes from the Arabic sāḥil (ساحل) describing a border, shore or edge, which aptly describes the transitional areas of Africa where savanna becomes the hyper-arid Sahara Desert. (According to the Concise Oxford Dictionary of World Place Names, "The Arabs considered the Sahara to be a huge ocean with the Sahel as its shore.") The Sahel crosses Senegal, The Gambia, Mauritania, Mali, Burkina Faso, Ghana, Niger, Nigeria, Cameroon, Chad, Central African Republic, South Sudan, Sudan, and Eritrea in a belt up to wide that spans from the Atlantic Ocean in the west to the Red Sea in the east. The Sahel is marked by decreasing levels of precipitation from south to north, but what defines a dryland ecosystem is not necessarily low rainfall. In some cases the dryness is due to persistent high levels of evaporation (due to heat or desiccating winds). Unpredictable rainfall is often also a factor. Population estimates of the Sahel vary depending on which political subdivisions are included, but the count is in the vicinity of 100 million people, including nearly a million refugees and internally displaced people. The countries of the Sahel region are mainly poor.