On the Ecology of Mountainous Forests in a Changing Climate: A ...
On the Ecology of Mountainous Forests in a Changing Climate: A ...
On the Ecology of Mountainous Forests in a Changing Climate: A ...
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Parameter sensitivity & model validation 131<br />
deviation from annual mean T (°C)<br />
10<br />
5<br />
0<br />
-5<br />
-10<br />
Jan<br />
Feb<br />
Mar<br />
Apr<br />
May<br />
Jun<br />
Jul<br />
Aug<br />
Sep<br />
Oct<br />
Nov<br />
Dec<br />
5<br />
4<br />
3<br />
2<br />
1<br />
0<br />
standard deviation (°C)<br />
fraction <strong>of</strong> annual precipitation<br />
0.4<br />
0.3<br />
0.2<br />
0.1<br />
0.0<br />
Jan<br />
Feb<br />
Mar<br />
Apr<br />
May<br />
Jun<br />
Jul<br />
Aug<br />
Sep<br />
Oct<br />
Nov<br />
Dec<br />
6<br />
4<br />
2<br />
0<br />
dev. <strong>of</strong> P (cm/month)<br />
std.<br />
Fig. 5.2: Analysis <strong>of</strong> <strong>the</strong> annual cycle <strong>of</strong> <strong>the</strong> long-term climatic parameters at <strong>the</strong> 12 study<br />
sites (Appendix III). Left: Average deviation <strong>of</strong> monthly mean temperatures from <strong>the</strong> annual<br />
mean temperature (open squares); average standard deviation <strong>of</strong> <strong>the</strong> monthly mean<br />
temperatures (black squares). Right: Average fraction <strong>of</strong> <strong>the</strong> annual precipitation sum<br />
fall<strong>in</strong>g <strong>in</strong> every month (open squares); average standard deviation <strong>of</strong> <strong>the</strong> monthly precipitation<br />
sums at 10 sites on <strong>the</strong> nor<strong>the</strong>rn slope <strong>of</strong> <strong>the</strong> Alps (black squares, exclud<strong>in</strong>g Airolo<br />
and Locarno). The error bars <strong>in</strong> both graphs denote one standard deviation.<br />
There is a confound<strong>in</strong>g factor <strong>in</strong>herent <strong>in</strong> <strong>the</strong> derivation <strong>of</strong> <strong>the</strong> monthly temperature data<br />
from <strong>the</strong> annual mean: The temperature amplitude <strong>in</strong>creases slightly <strong>in</strong> drier climates, and<br />
this is <strong>the</strong> reason why <strong>the</strong> alp<strong>in</strong>e timberl<strong>in</strong>e <strong>in</strong> Fig. 5.1 is found at lower annual mean<br />
temperatures as precipitation decreases. L<strong>in</strong>ear regressions <strong>of</strong> <strong>the</strong> annual temperature amplitude<br />
aga<strong>in</strong>st <strong>the</strong> annual precipitation sum from various subsets and <strong>the</strong> whole set <strong>of</strong> <strong>the</strong><br />
12 climate stations (Appendix III) generally yielded <strong>in</strong>significant correlation coefficients,<br />
but <strong>the</strong> <strong>in</strong>tercept was always close to 20 °C, and <strong>the</strong> slope varied between -0.002 and<br />
-0.0009. In spite <strong>of</strong> <strong>the</strong> <strong>in</strong>significance <strong>of</strong> <strong>the</strong> regressions, <strong>the</strong> follow<strong>in</strong>g approximation for<br />
<strong>the</strong> effect <strong>of</strong> <strong>the</strong> annual precipitation sum (P l ) on temperature amplitude (A l ) was used to<br />
reconstruct <strong>the</strong> annual cycle <strong>of</strong> monthly mean temperatures:<br />
A l ≈ 20 – 0.0014 · P l (5.1)<br />
Based on <strong>the</strong>se considerations, <strong>the</strong> long-term mean monthly temperature (T m,l ) is calculated<br />
from <strong>the</strong> annual mean temperature (T l ) and <strong>the</strong> annual precipitation sum (P l ) accord<strong>in</strong>g<br />
to Eq. 5.2:<br />
T m,l = T l + ∆T m · (1180 – P l)·0.0007 + |∆T m |<br />
|∆T m |<br />
(5.2)