Geoscience Reference
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on agricultural production, and were expressed as a percentage
change in estimated average yield in the period 1980-2000.
19.4
Discussion of results
General
findings
The regression results show that there is a positive effect of
increased GDD (temperature) on yield per decare only for some
crops, counties and time periods; confer Table 19.1 (see Annex
19.1 for a detailed account of results). Overall, about 18% of the
236 cases have a significant and positive GDD coefficient. For
3% of the cases, the GDD coefficient is negative and significant.
In the case of crops, there are most significant results for pota-
toes. In terms of regions, the most significant results are found
for Northern, Mid-, Western and Southern Norway. Sunlight and
high temperatures are more likely to be a limiting factor in north-
ern and western counties than in the south and east. Coefficients
for potatoes are between 1.0 and 3.0, with the highest values evi-
dent in Northern Norway. This means that an increase of one
GDD unit induces a yield increase of 1-3 kg per decare.
*
In addi-
tion, there are positive coefficients for barley in seven counties
situated in Western and Mid-Norway, and in Nordland. The coef-
ficients are between 0.13 and 0.27. There are also a few significant
coefficients for oats ranging from 0.16 to 0.31. These results are
consistent with the findings of Leemans and Soloman [8] since
high-latitude regions are the primary beneficiaries of a warmer
climate. They also reinforce the hypothesis that temperature is
a more important limiting factor for crop growth in Northern
and Western Norway than in other regions of the country such
as Southern and Eastern Norway, where the weather conditions
provide higher temperatures during the growth season.
The effect of increased annual precipitation on yield is nega-
tive and significant for many counties and crops, in particu-
lar, for Western and Mid-Norway, and for Nordland (20% of
all cases). On the other hand, 5% of the cases give a positive
and significant precipitation coefficient. Another study that
finds a negative impact from increased precipitation on agri-
cultural production is Rosenzweig et al. [19], where a dynamic
crop model is modified to simulate effects of heavy precipi-
tation and excess soil moisture on corn production in the US
Corn Belt. The few positive coefficients are found in Eastern
Norway. The coefficients range from −2.5 to 1.9 for potatoes,
*
GDD increases by one unit if the average temperature on a particular day in
the growing season increases by 1°C from a minimum base of 5°C.
