The assessment of effects of climatic variations on agriculture: a summary of results from studies in semi-arid regions

Abstract

This section outlines the aims and methods of the IIASA/UNEP project on the assessment of the effects of climatic variations on agriculture. It summarizes the results from case studies in semi-arid regions. Two broad types of experiment are described: impact experiments and adjustment experiments. Crop yields in all regions are very sensitive to seasonal rainfall amount, many exhibiting a positive linear or near-linear relationship over a typical range of climatic conditions. Moreover, this relationship appears to hold for crops grown under high as well as low levels of farm inputs (i.e., management and technology). Within-season variations in rainfall also contribute to crop yield variability, having a marked effect, in addition, on the quality of forage and hence on livestock nutrition. Concurrent effects of climatic variations on fertilizer responsiveness, on soil moisture status and on longer-term soil nutrient status, which complicate the direct climate-yield relationship are examined, and experiments with adjustments to these (e.g., altered amounts and timing of irrigation or fertilizer application, fallowing practices, planting techniques, etc.) are reported that evaluate the potential for increasing or stabilizing crop productivity. A range of adjustments to cope with drought effects are described, both at the farm level (including ex ante adjustments to optimize production and ex post adjustments to minimize losses) and at the public policy level (including food supply measures, ecological and infrastructural interventions and adjustments in land allocation). Finally, some gaps in knowledge are identified and a number of priorities for future research are outlined. -from Editors