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a. Logarithm of net revenue per hectare.

b. Mendelsohn, Dinar, and Sanghi (2001). See appendix G.

a. Logarithm of net revenue per hectare.

b. Mendelsohn, Dinar, and Sanghi (2001). See appendix G.

(see appendix G). A summary analysis estimates cross-section Ricardian functions relating net revenue per hectare to linear and quadratic terms for seasonal temperature and precipitation. Once again nonclimate variables have the effect of shifting the net revenue estimate by a constant K. Application of the base and future climate variables provides the basis for estimating the change in net revenue from climate change (excluding the effect of carbon fertilization and changes in water runoff, a variable in these cross-Africa functions).

Table 5.3 shows the results of applying the World Bank Ricardian functions for Africa to the base and future climates, again using seasonal monthly climate data (see appendix G for model parameters and appendix H for country-level averages of the underlying grid-level monthly climate data, although the actual estimates are calculated at the much more detailed standard grid level). It then expresses the change in net revenue per hectare as a percent of the all-Africa average base level of output per hectare.11 Even though average net revenue and output per hectare will

11. Once again it is necessary to estimate the relationship of base net revenue per hectare to base output. As reported in table 5.4, for all of the African countries considered, total dryland farm area is 193.4 million hectares, and total irrigated farm area 13.44 million hectares. Agricultural value added for the region is a total of \$100.2 billion. The World Bank sample showed average net revenue per hectare for irrigated land was four times as large as that for dryland. Using this same ratio, agricultural GDP can be estimated to have averaged \$405 per hectare for dryland and \$1,622 per hectare for irrigated land. That is, 13.44 X 106 X qd X 4 + 193.4 X 106 X qd = \$100.2 X 109. Solving for output per dryland hectare, qd = \$405, and output per irrigated hectare is four times as much, or \$1,622. From the sample, net revenue was an average of \$319 per hectare for dryland and \$1,261 per hectare for irrigated land. Net revenue is thus a relatively high 78 percent of agricultural GDP per hectare. The high ratio likely reflects substantial incidence of the use of family labor relative to hired labor and purchased inputs in a relatively low-income region.

Table 5.3 Impact of climate change by the 2080s on African agriculture, World Bank Ricardian models (without carbon fertilization)

Net revenue per hectare estimate excluding nonclimate variables (2005 dollars) --Change as percent of base

Base Future output/hectare, Africa average

Country/region

Dryland

Irrigated

Dryland

Irrigated: A

Irrigated: B

Dryland

Irrigated: A

Irrigated: B

Algeria

0 0