Geoscience Reference
In-Depth Information
As soon as spring arrives the gap increases again. Man-made surfaces, where
asphalt surfaces dominate, become dry and heat up again quickly. It is at this
moment that vegetation also starts to grow. Surfaces on which significant amounts
of vegetation are present do not retain any heat due to the process of
evapotranspiration. Temperature in these areas is lower in comparison to areas
where there is much less vegetation. This trend continues into the middle of the
summer for climatological stations that are located in woodland areas.
This same trend stops in April and then the reverse of this trend occurs until the
month of August for CLC posts located in extensive open spaces. The growth of
vegetation in open spaces is at its maximum in spring and as a result the processes
of haymaking and harvesting make cultivated areas similar to mineral surfaces as far
as temperature is concerned.
2.4.2.3.
Estimating the NDVI by transforming qualitative CLC values into
quantitative values
This model provides us with the tools required so that each of the CLC codes
can be provided with quantitative values. Negative coefficients are associated with
climatological stations found in relatively cool areas. These coefficients are given
negative values because the biomass found in such cool areas is significant. A
positive coefficient value is given to CLC land cover types that are part of the built-
up area category where biomass is low. The reference value for each group of CLC
land cover type is obtained by multiplying the annual coefficient by 100 (see Table
2.1).
woodland
spaces
built-up areas
complex zones
open spaces
Value
55
-10
-90
-135
Table 2.1.
Quantitative values allocated to the main land cover types
as recognized by the CLC
If a particular category corresponds to a similar CLC land cover type, only one
quantitative value is allocated to this particular land cover type. For example, the
group woodland spaces, which includes leaved forests and coniferous forests, has a
value of -135, and there is no distinction made between the two types of forests.
This is not the case, however, for areas composed of artificial surfaces (built-up
areas, see Table 2.1) which are made up of approximately 10 different man-made
types. The reference value of 55, which is the reference value for the entire group,
will vary depending on the manmade material in question and in proportion to the
actual amount of mineral surface that makes up the type. This is why a value of 110
was given to continuous urban material, in other words this part of the group has
twice as much mineral surface in it when compared with the overall average for the
entire group. Urban green spaces, which have a significant amount of vegetation,
are allocated a value of 20 (which is a little less than 55/2). This is because there is
half the amount of mineral surface in this area. Uncertainties arising from this
process include a difficulty in estimating exactly how much built-up area and
