Scientists at IITA have been concerned about climate change and what it portends for agriculture. They have studied rainfall data in Nigeria over a 30-year period (1961-1990) using figures available from national programs, and they seek to catalyze similar studies in other countries. The Nigerian study provides evidence of climate change and indicates the kinds of agricultural technologies that would lessen its effects.
Using a decade as the unit of comparison, annual rainfall has declined over both time and space. Reductions varied from 100 to 313 millimeters depending on topography and location. There has been a southward shift (toward the ocean) of isohyets, or lines of equal rainfall, from 75 to 200 kilometers. While there appeared to be little change in total rainfall in areas with an annual mean precipitation greater than 1700 mm, shifts were considerable in low-rainfall areas.
In short, dry areas are getting drier and, if the trend continues, it will lead eventually to desertification.
The greatest changes occurred in the onset of the rainy season and the extent of early rainfall. Increasingly, there has been less rain in the first month of the season, followed by a proportional increase in the second month. Delayed onset of rains has also tended to shorten the growing season overall by about a month. These changes will delay planting as early planting becomes increasingly risky. The shortening of the growing season will affect the kinds of crops that can be grown profitably.
Throughout Nigeria, there were fewer wet days per season, but the intensities of rainfall were greater. The fewer wet days underscore the need to conserve water and soil moisture, while greater rainfall intensities mean greater erosion hazards. Intense rainstorms cause soil erosion and the runoff water carries away nutrients with the topsoil. Erosion also reduces the organic-matter content of the soil, leading to reduced water-holding capacity.
Research to relieve the impacts of these changes would include development of technologies to conserve soil moisture, increase soil organic matter, and reduce soil erosion. Also required is research to increase crop diversity in terms of both species and maturity periods to enable farmers to select crops to fit rainfall regimes.
Some of the results of IITA's past research are pertinent to solving the problems posed by changes in rainfall. These include minimum tillage, the use of mulches, and the practice of tied ridges to reduce soil erosion and conserve soil moisture. Among the advantages of alley farming systems is erosion control. When the shrubs or trees used in alley farming are planted along the contours of sloping land, they reduce erosion considerably, and they may also act as windbreaks to soften the erosive impact of intense rainfall.
(IITA news release)