Environmental Engineering Reference
In-Depth Information
Climate change predictions do not come without assumptions and uncertain-
ties, and therefore their projections should be interpreted carefully. For example, an
average warming of 3
◦
C may well mask the real results used to calculate this aver-
age, or in simple terms, a model realization could predict a 1
◦
C increase in temper-
ature and another realization a 5
◦
C increase, with 3
◦
C being the average value. This
huge difference among different projections and their influence on predicted im-
pact needs more studies to explain the degree of uncertainty in climate projections.
For example, predicted changes of precipitation in Mediterranean mountains differ
noticeably among AOGCMs and emission scenarios (Nogues-Bravo
et al.,
2008a).
For 2055, the greatest reduction of average annual precipitation for Mediterranean
mountains was 12.5%, whereas other models projected an increase of 0.9%. A sim-
ilar pattern was recorded for 2085, although the difference among projections was
greater for 2085 (23% and 1.4%, respectively).
In the paragraphs above we have summarized the projected climatic trends for
the twenty-first century, which show mainly an increase in temperature and a de-
crease in rainfall. This trend was also significant during the twentieth century. To
assess this climatic trend, we have analyzed the moisture trends in the six moun-
tain ranges using a drought index: the Standardized Precipitation Evapotranspira-
tion Index (SPEI) (Vicente-Serrano
et al.,
2010). This index combines the effect of
precipitation inputs and temperature demand in the moisture conditions. Using a
climatic dataset (P.D. Jones
et al.,
in preparation; http://badc.nerc.ac.uk/data/cru/)
from 1901 to 2006, we obtained annual (January to December) SPEI values for
each one of the 0.5
◦
pixels corresponding to each of the six mountain ranges an-
alyzed here. Trends in moisture for each mountain range were calculated using
the non-parametric Mann-Kendall test (
p
0.05). Table 9.1 shows the percentage
of surface in each mountain range with positive (increase of moisture conditions)
and negative trends (decrease of moisture conditions), and a clear domain of neg-
ative and significant trends in most of the mountain ranges. It is remarkable that
those mountain ranges located in the westernmost areas (Atlas, Pyrenees and Apen-
nines) show the highest percentage of the surface area with negative and significant
trends. Thus, the Atlas shows the clearest decrease in moisture conditions among
the six analyzed mountain ranges, with 95.6% of the surface affected by negative
trends (see also Figure 9.3 showing the evolution of the SPEI in each of the six
mountain ranges).
Table 9.1
Percentage of the surface area with negative and positive trends in the Standardized
Precipitation Evapotranspiration Index (SPEI) values for each mountain range
Trend
Pyrenees
Apennines
Dinaric Alps
Pindos
Taurus
Atlas
Negative (sig.)
85.7
67.7
8.3
35.7
51.7
95.6
Negative (non-sig.)
14.3
32.3
75.0
64.3
48.3
4.4
Positive (non-sig.)
16.67
