Climate Change, Global Warming, and Agricultural Droughts - Monitoring and Predicting Agricultural Drought: A Global Study - page 445

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areas was caused by strong dust storms in the 1930s. The A -indicator val-
ues for winter wheat calculated for a long period for the Oklahoma and
Texas grain areas were about 0.23. In central and northern areas of the
U.S. wheat belt the stability of winter wheat yield was a little higher, with
the A-indicator ranging from 0.15 to 0.20.
The absence of the winter soil freezing and the uniform annual distribu-
tion of atmospheric precipitation allows one to obtain rather stable yields
of winter wheat in the forest-steppe areas of the U.S. corn belt. For agri-
cultural areas of Ohio, Indiana, Illinois, Missouri, and Iowa, A-indicator
ranged from 0.10 to 0.15, though it is also possible to note some tendency
toward an increase in the value of this indicator in the western parts of this
area where the climatic normal of moistening is lower. For the southern
Atlantic U.S. states, the A-indicator was 0.15. In general, the A-indicator
for spring wheat in North America remained between 0.10 and 0.30.

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Sp ecific 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 recom-
mended 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, accord-
ing to the Holocene and Pliocene optimum analog scenarios, which cor-
respond 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 calcu-
lated 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 warm-
ing 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

Line
——
-0.1
——
Norm
PgEn

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