08.09.2014 Views

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 ...

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

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)

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!