Climate sensitivity

Our experiences with various climate sensitivity scenarios and preliminary results with GCM based climate scenarios (Climate scenarios) underpin the appropriateness of the AEZ methods for climate change impact assessments. It confirms findings of earlier work with AEZ applications in case studies of Kenya (Fischer and van Velthuizen, 1996) and Nigeria (Voortman et al., 1999), demonstrating that AEZ is very flexible in capturing all three types of impacts, namely on yields, on extents suitable for crop cultivation, and on changes in number of crops per year (sequential multi-cropping). It thus accounts for a wide range of rational adaptations, i.e., simulating impacts to ‘smart’ farmers. Recently, a number of experiments with GCM derived climate change scenarios has been completed. A detailed report with results of these simulations on AEZ crop suitability and productivity is in preparation (Fischer and van Velthuizen, forthcoming).

Meanwhile, in order to demonstrate possible effects of climate change on potential distribution patterns of some key crops, a limited set of temperature and rainfall sensitivity scenarios were applied as follows:

• Respectively 1°C, 2°C, and 3°C temperature increase uniformly in each month for both minimum and maximum temperatures, and
  
  
• Uniformly distributed combined increases of temperature and precipitation of respectively 1°C and +5% monthly precipitation, temperature increase of 2°C and +5% monthly precipitation, 2°C warming combined with +10% change of annual precipitation, and 3°C warming combined with +10% change of annual rainfall, distributed proportionally over the twelve months.

The application of this set of temperature and rainfall sensitivity scenarios revealed a modest increase of cultivable rain-fed land for temperature increases up to 2°C on global scale. With a higher temperature increase alone, extents of cultivable rain-fed land start to decrease. When both temperature and rainfall amounts increase, the extents of cultivable rain-fed land increase steadily. For example, a temperature increase of 3°C paired with a rainfall increase of 10 percent, would lead to about 4 percent more land globally suitable for rain-fed cultivation of wheat, rice, or grain-maize. In the developed countries this increase is even markedly higher; it exceeds 25 percent. Contrariwise, for developing countries there would be a decrease of 11 percent.

Potential distribution of rain-fed grain maize for control run, +2°C, and +3°C combined with +10% annual rainfall.

The maps show considerable shifts of the potential distribution even when modest changes of temperature or rainfall are applied.

	Selected temperature and rainfall sensitivity scenarios the impacts on extents of very suitable, suitable, and moderately suitable land for wheat.
	Selected temperature and rainfall sensitivity scenarios the impacts on extents of very suitable, suitable, and moderately suitable for wheat, rice and grain maize combined.