Environmental Engineering Reference
In-Depth Information
are currently close to complete disappearance (D'Orefice
et al.,
2000; Lopez-
Moreno
et al.,
2006). Other mountain ranges next to the Mediterranean Basin,
such as the Alps, are among those exhibiting the greatest glacier retreats worldwide
(Oerlemans, 2005). Thus, a dramatic degradation in Mediterranean glaciers is very
likely under the warming magnitudes projected by climate models.
9.4 Hydrosphere changes in the
Mediterranean mountains
Mountains provide various ecosystem services (Nogues-Bravo
et al.,
2008a), both
within the mountain ranges and also to neighbouring lowlands, and among them
the most important in Mediterranean mountains is water. Therefore, the hydro-
sphere changes in mountain ranges drastically affect water supply across the whole
Mediterranean basin. Specifically, a significant relationship has typically been ob-
served across all temporal scales (regardless of the basin area studied or geomor-
phological and geological characteristics) between the temporal evolution of pre-
cipitation, at annual or longer scales, and river discharge.
The role of temperature in the evolution of water resources is generally more dif-
ficult to assess than that of precipitation. However, some studies have confirmed that
warming has a role in explaining recent trends in water resources in the Mediter-
ranean Basin. Thus, Pandzic
et al.
(2009) attributed the decrease since 1950 in dis-
charge from the Sava River (Croatia) to a negative trend in soil moisture availability,
which is closely related to increased evapotranspiration. A similar conclusion was
found for the headwaters of the Duero River in the Iberian Peninsula (Ceballos
et al.,
2008).
As expected from the changes in precipitation and temperature, a generalized and
consistent decrease in river discharge has been reported in all studies concerning
this aspect of the Mediterranean Basin (Lopez-Moreno
et al.,
2008).
The occurrence of severe droughts has affected the duration and severity of low
flow periods, which have significant ecological, economic and social impact. For
instance, Zanchettin
et al.
(2008) analyzed the evolution of stream flow in the Po
River, northern Italy, since the beginning of the nineteenth century; no changes in
average annual discharge during the twentieth century were found. Nevertheless,
the cited authors found an increase in peak flow discharge in recent decades, and a
higher frequency of drought periods since 1940. Snow accumulation and snowmelt
play a determining role in the seasonal distribution of river discharge, especially in
mountain basins in the Alps, the Carpathians, the Balkans, and the Pyrenees. As a
consequence, higher discharge is usually expected in spring, when snowmelt and
rainfall combine to give high flows between April and June.
Global warming affects snow accumulation and snowmelt in two ways: (i) reduc-
ing snow accumulation in the headwaters and giving more rain events in winter; and
(ii) causing earlier thawing in the season. Both responses cause major changes in
