# **1. Introduction**

In many African countries agriculture will remain an important sector for promoting growth, supporting rural livelihoods and reducing poverty for several decades to come (IFAD 2001). In addition to low productivity levels, degradation of natural resources and lack of investment in rural infrastructure, climate change represents a significant challenge for agro-ecosystems in the region (Rosenzweig & Parry 1994). There is increasing consensus among experts that the impacts of human activity on the global climate system are already felt in many parts of the world and are likely to affect the most vulnerable regions and sectors in the near future (IPCC 2001). For the African region, an important question therefore is how projected trends in climate are going to affect agriculture and, by extension, food security, sustainable use of natural resources, and economic development. The work presented here investigates the sensitivity of current cropping patterns in Africa to seasonal perturbations in climate and assesses the potential impact of transient climate change suggested by climate model scenarios.

Since the emergence of agriculture farmers have developed techniques to overcome the biological and physical constraints that climate and land pose for the production of crops, including irrigation, land terracing and fertilization. Despite these agricultural management practices, crops remain ultimately dependent on ecological conditions, such as the intraseasonal distribution of precipitation and temperature, soil fertility and length of growing season. While cropping in boreal regions is limited by low temperatures and a short growing season, cropping in tropical and subtropical regions tends to be limited by inadequate moisture conditions and high temperatures (Cramer & Solomon 1993). Recent work on the impacts of climate change suggests that countries in tropical latitudes will experience negative effects on economic development as a consequence of further warming and changes in precipitation patterns (Mendelsohn et al. 2000).

To assess climate change impacts on cropping patterns in Africa, this work (i) quantifies the extent of croplands across a variety of agro-ecosystems, (ii) relates current cropping patterns to climate, soil and terrain attributes through empirical models, and (iii) predicts how these patterns are likely to change based on the transient changes in climate projected by global Atmosphere-Ocean General Circulation Models (AOGCMs). This work is part of a wider effort to understand the economic effect of climate change on agriculture and the way farmers adapt in response to agro-ecological conditions (Dinar et al. 2006).

# **2. Data on current cropping patterns in Africa**

To estimate the impact of climate change on cropland patterns across a variety of agroecological and climatic zones, geographically continuous representations of croplands, climate and other physical land properties were used. To do this, the continental land area was partitioned into grid cells of .5° latitude by .5° longitude (about 50–60 kilometer square grids in tropical and subtropical regions) and all variables described below were assimilated to the same data grid.

Because of the lack of sufficient, consistent and geographically coherent data on cropping systems for the whole of Africa, this analysis uses global land cover inventories derived from satellite observations in conjunction with ancillary statistical data on land use and agricultural 4