Agriculture Reference
In-Depth Information
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nate the territories now unsuitable for agriculture (deserts, tropical woods,
polar areas and regions with complex topography and also the territories,
where the difference between the annual precipitation and potential evap-
oration is
>
200 mm), the remaining areas may be regarded as agricultural
ones. According to the agroclimatological estimates, more than 50% of
agricultural land can be endangered by drought.
One of the most important consequences of global warming is degrada-
tion of drylands (chapter 33) in different regions of the world. It is impor-
tant to determine the principal consequences of expected regional climate
changes caused by modern global warming in agriculture of different re-
gions and whether they will result in increasing the occurrence and severity
of droughts or whether droughts will become less frequent. In the subse-
quent sections of this chapter we present some preliminary answers to this
question.
[434
W
heat Yield Variation and Prediction in Some Countries
Crop prediction in some countries can be studied in relation to recorded
climatic change in recent years using prediction models. Wheat yield data
were collected from the U.N. Food and Agriculture Organization (FAO)
for 55 countries for the last 40 years. Analysis of the long-term changes
in wheat yields is interesting for three reasons. First, wheat is the most
widely cultivated crop in many countries. Second, the areas of wheat cul-
tivation are often more affected by drought than other main crops. Third,
the archive of data on wheat production is the largest and most reliable.
We selected relatively small regions or countries because the yields in large
territories experience a greater spatial variability. Unfortunately, full in-
formation about the crop yields for smaller and climatically homogeneous
areas is often not available.
Line
——
-0.2
——
Long
PgEn
[434
U
nited States
Figure 34.1 shows different yield anomalies, (
y
y
t
)/
y
t
, for the U.S. states
Colorado, North Dakota, and Kansas. These curves show the important
regularity that, despite significant distinctions in meteorological conditions
in these three U.S. states and their remoteness from each other, the principal
features of their annual variability are similar. The five-year smoothed
averaged values of relative anomalies were mainly positive during 1900-
17, 1940-48, and negative during 1918-39.
In addition to the annual or five-year mean variability, yield variabil-
ity can also be studied using the hydrothermal coefficient (HTC) and S
index that are widely used for drought monitoring in the former Soviet
Union (chapter 15). The variations in these indices for the above U.S. states
are shown in figure 34.1. The meteorological data used for computing
these indices were collected from three meteorological stations: Denver (for
Colorado), Bismarck (for North Dakota), and Kansas City (for Kansas)
−
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