Climate Change, Global Warming, and Agricultural Droughts - Monitoring and Predicting Agricultural Drought: A Global Study - page 436

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Figure 34.1 continued

and tractors (relative numbers/ha) available, electric power, and pesticides
and herbicides used have been included in the calculations. In the case of
Bulgaria the correlation coefficient between η 5 (5-year smoothed relative
yield anomaly) and S 5 (five-year smoothed S index) is 0.51. Wheat yield
anomaly was positive from 1970 to 1992. The deviations of annual yields
from the technological trend during this period were mainly positive. In one
unfavorable year, 1985, the wheat yield in Bulgaria fell to 11% below the
trend. After 1983 the yield anomaly trend entered into a declining phase,
and after 1992 the wheat yield anomalies were mainly negative. In 1996 a
serious failure in wheat production took place, when yield was 47% below
the trend.
Figure 34.3 shows wheat yield anomalies during 1960-2001 for several
other European countries. By studying the trends in anomalies one can
conclude that the 20-year period, from the beginning of the 1970s until