Water Balance in Catchments
279
comes a simple function of the quotient PIEr. This simple model also shows
graphically why the relationship EA-P is significant at low values but not at
high values of PIEr, and the opposite for the relationship Q-P. At low values of
PIEr (arid catchments) the slope of Eq. (19.1) (EA/Er) is close to the unity
and the relationship P-EA is significant. On the other hand, at low values of
PIEr, the slope of equation 19.2 (Q/Er) is close to zero, and the natural variability obscures any significant relationship between P and Q. At high values
of PIEr (humid catchments) the slope of Eq. (19.1) is close to zero and that of
Eq. (19.2) is close to unity, making non-significant the relationship P-EA and
significant the relationship P-Q.
19.5 Representativeness of the Experimental Catchments
for Larger Areas
One of the main concerns about small, experimental catchments is whether
the results obtained can be interpreted and extended to larger areas of the
same physiographic region. The representativeness of the Prades and Montseny experimental catchments was evaluated in a previous work (PHiol et al.
1992) by comparing them to the streamflow record of two larger, mainly forested, catchments located in both mountainous massifs (Siurana, 60 km 2 , at
Prades; Llavina, 34 km 2 , at Montseny). It was found that the experimental
catchments at both Prades and Montseny produced less annual streamflow
than larger catchments in the same region. The main reason for this seems to
be the larger proportion of forest cover in the experimental catchments
(nearly 100%) than in the larger ones (74% at Llavina and 30% at Siurana).
Nevertheless, flow duration curves and the annual water balance were more
similar between small and large catchments within the same region than
between the physiographic regions of Prades and Montseny, thus reinforcing
confidence of the results obtained in the small experimental catchments of
Prades and Montseny.
19.6 Water Balance in a Warmer Climate
The increase of atmospheric CO2 and other greenhouse gases during this
century is probably changing the Earth's climate. At every new edition of the
Intergovernmental Panel on Climatic Change (IPCC) conclusions, more evidence is given of the direct link between the change in the composition of
the atmosphere and climate change. It seems clear that the Earth's temperature has already increased in this century and that it will further increase in
the near future (Houghton et al. 1996). In the Mediterranean region of Spain
this increase of temperature has already been observed (0.10 °C per decade,
279
comes a simple function of the quotient PIEr. This simple model also shows
graphically why the relationship EA-P is significant at low values but not at
high values of PIEr, and the opposite for the relationship Q-P. At low values of
PIEr (arid catchments) the slope of Eq. (19.1) (EA/Er) is close to the unity
and the relationship P-EA is significant. On the other hand, at low values of
PIEr, the slope of equation 19.2 (Q/Er) is close to zero, and the natural variability obscures any significant relationship between P and Q. At high values
of PIEr (humid catchments) the slope of Eq. (19.1) is close to zero and that of
Eq. (19.2) is close to unity, making non-significant the relationship P-EA and
significant the relationship P-Q.
19.5 Representativeness of the Experimental Catchments
for Larger Areas
One of the main concerns about small, experimental catchments is whether
the results obtained can be interpreted and extended to larger areas of the
same physiographic region. The representativeness of the Prades and Montseny experimental catchments was evaluated in a previous work (PHiol et al.
1992) by comparing them to the streamflow record of two larger, mainly forested, catchments located in both mountainous massifs (Siurana, 60 km 2 , at
Prades; Llavina, 34 km 2 , at Montseny). It was found that the experimental
catchments at both Prades and Montseny produced less annual streamflow
than larger catchments in the same region. The main reason for this seems to
be the larger proportion of forest cover in the experimental catchments
(nearly 100%) than in the larger ones (74% at Llavina and 30% at Siurana).
Nevertheless, flow duration curves and the annual water balance were more
similar between small and large catchments within the same region than
between the physiographic regions of Prades and Montseny, thus reinforcing
confidence of the results obtained in the small experimental catchments of
Prades and Montseny.
19.6 Water Balance in a Warmer Climate
The increase of atmospheric CO2 and other greenhouse gases during this
century is probably changing the Earth's climate. At every new edition of the
Intergovernmental Panel on Climatic Change (IPCC) conclusions, more evidence is given of the direct link between the change in the composition of
the atmosphere and climate change. It seems clear that the Earth's temperature has already increased in this century and that it will further increase in
the near future (Houghton et al. 1996). In the Mediterranean region of Spain
this increase of temperature has already been observed (0.10 °C per decade,