Geoscience Reference
In-Depth Information
Yield
predictions for
the RegClim
scenario
The equation for predicting yield per decare for crop i in county
j under the RegClim climate change scenario, Y ijR , is
·
··
ˆ
·
·
·
Y
=+ +
αβ γ
T
P
+
θ τ
ijR
ij
jR
jR
R
ij
ij
where ˆ jR is GDD and ˆ jR is precipitation in the RegClim sce-
nario in county j, and τ R is the time trend in 2040 (represent-
ing the RegClim period 2030-2050). R is the index for the
RegClim scenario.
19.3 Data
The dependent variable is yield per decare for each of the crops
potatoes, barley, oats and wheat. The independent variables are
the weather data GDD and annual precipitation, in addition to
the time trend.
time periods
For each crop and county, analyses were undertaken for the
main period 1958-2001, given that the required data were
available. In the absence of sufficiently comprehensive data
at county level to enable the incorporation in the model of a
variable for technological change, national fertiliser-use figures
were examined for clues as to what sort of impact one might
expect farming practices to have had on crop yields from the
1950s until today. * It appeared that the 44-year period of our
study could be split into three 'phases' with respect to fertiliser
consumption (in terms of the total value of all varieties sold).
The first phase, from 1958-1973, saw a slow, steady increase in
the amount of fertiliser bought, the second, from 1974-1988,
demonstrated a continuous, sharp rise in sales, while the third
phase, 1989-2001, was less clearly defined, but illustrated an
overall declining trend. In light of this information, separate
regressions were conducted for each of these three time peri-
ods. If yields were found to have responded differently during
the three phases, this might be detected when we compared
each sub-set of the analysis.
Crop data
Annual yield data were supplied by Statistics Norway and
collected at county level for each of the four crops in this study
* Budsjettnemnda for jordbruket, NILF (Norwegian Agricultural Economics
Research Institute), 2002.
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