Specific Predictions of Future Droughts

Several authors have carried out calculations of possible changes in agrocli-matic regime and wheat crop productivity over the former USSR grain belt using different scenarios of global climate changes (Menzhulin et al., 1995; Budyko and Menzhulin, 1996; Menzhulin, 1997). However, it is difficult or even impossible to identify the best model. The climate model recommended by IPCC cannot fully represent the present regime of atmospheric precipitation (Menzhulin, 1998a, 1998b; Houghton et al., 2001).

Figure 34.7 shows the correlation diagram of the statistical dependence between the normal annual precipitation and the A-indicator of the wheat yield abnormality. This is based on the IPCC predictions of the global mean annual temperature and precipitation changes in 2010 and 2050 for regions in the former USSR, European countries, and U.S. states.

In table 34.1 we present the results of our assessments of the changes in the A-indicator for wheat, as applied to some Russian regions, European countries, and U.S. states for climate changes in 2010 and 2050, according to the Holocene and Pliocene optimum analog scenarios, which correspond to global warming by 1°C and 3-4°C, respectively. In table 34.1 the changes in climatic normals of wheat productivity, which were calculated previously with the use of the specially developed crop productivity model, are also presented. This model takes into account the influence of the temperature and precipitation changes as well the atmospheric increase in carbon dioxide on the crop productivity in 2010 and 2050 (Menzhulin et al., 1987). The positive values of the wheat climatic productivity changes indicate a gain of potential productivity (i.e., a favorable change), but the positive values of the A-indicator show an increase of the annual variation in the amplitude of the wheat crop yield (i.e., an unfavorable change).

From table 34.1, it is noticeable that during the period of global warming until 2010, some increase in agricultural drought occurrence is possible in the U.S. states. It also shows a favorable impact of the expected climate

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Figure 34.7 The correlation between normal annual precipitation (mm) and A-indicator (A) of wheat yield abnormality.

changes on the climatic normal for wheat productivity in U.S. states, where this impact is usually less than in the Russian regions and in European countries. But later in the phase of higher global warming in the middle of this century, the effect of partial drought that increased in some U.S. states in the first decade of this century will vanish because the atmospheric precipitation in agricultural regions of the United States, Russia, and Europe will increase, according to the Pliocene optimum scenario.

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