In addition to changing their crop mix, farmers could also change how much land they farm or the way in which they farm what they have. Introducing irrigation into currently rainfed systems is an often cited adaptation option, and will indeed likely be critical for some regions. As mentioned, irrigation not only alleviates water stress but could expand the opportunities for switching planting dates and varieties, as well as increasing returns on investments in fertilizer and other inputs. Large scale expansions of irrigation infrastructure are typically financed and regulated by the public sector, and therefore farmers often cannot decide on their own to implement irrigation.
NAmer Russia SAmer EAfr WAFr SAfr SAsia SEAsia
Fig. 8.3 Percent change in land suitability for rainfed cereal production, for selected regions by 2080 (Hadley model, A2 scenario) (from Fischer et al. 2002)
But in some systems irrigation may represent a truly autonomous adaptation, for instance if a treadle pump is installed to irrigate a small number of fields.
There is also considerable scope for implementing technologies that improve soil moisture without irrigation, such as conservation tillage and rainwater harvesting (Ngigi et al. 2005; Hobbs et al. 2008). The latter includes techniques such as farm ponds and zai pits, and may be increasingly relevant if rainfall becomes more episodic and intense, as suggested by many climate models (Chapter 3).
In areas currently too cold or dry to support rainfed agriculture, climate change might enable the expansion of cropped area into new regions. If such expansion is deemed socially and environmentally acceptable, then gains from production in these new areas could offset potential regional or global losses elsewhere (see Section 8.5).
Figure 8.3 shows one estimate of regional changes in the amount of land suitable for rainfed production, based on the agro-ecological zoning (AEZ) model and output from one climate model (Fischer et al. 2002). High latitude temperate regions generally gain and tropical areas generally lose suitable land in these projections, with changes exceeding 40% in either direction by the end of the century for some climate scenarios. Critical uncertainties in these projections are assumptions about soil constraints in these new regions, which are usually incorporated into assessments but on the basis of scant data. Improving the accuracy and use of soil information in these regions is a major need for determining future potential of expansion in places like Canada and Russia.
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