13.1 Introduction
Amongst many other ecological functions, mountains play a major role as freshwater reservoirs, this being especially relevant in arid and semi-arid regions
(Viviroli et al. 2007). Either in the form of aquifers, lakes, snow or ice cover, the
water stored by mountains often represents the principal source of water for most
populated areas that are usually located downstream. Thus any process involving
changes in the hydrological cycle in the mountains, e.g. in climate variables, land
cover, soil properties, or snow cover (Arnell 1999; Foley et al. 2005; Stewart et al.
2005; Bormann et al. 2007; López-Moreno et al. 2011), will have an impact on
water availability downstream. Recent observed worldwide warming is inducing
environmental changes in high mountains related to their capacity for storing water,
including a decrease in the accumulation and accelerated melting of snow, the
consequent reduction in the duration of the snowpack, the receding of glaciers and
the loss of permafrost (Barnett et al. 2005; Lemke et al. 2007; Adam et al. 2009).
Mountains and the process of snow accumulation-melting are hotspots for climate
change impacts (Beniston 2003), due to the high sensitivity of the snow cover to
seasonal temperatures, especially in low-to-middle elevation sites (Morán-Tejeda
et al. 2013). Streamflow, as the ultimate output of mountain systems, will reflect
these environmental signals by changing its timing and magnitude, and thus
becomes not only a vital resource for populations, but also an important indicator of
environmental changes, including global warming, for scientific research.
Climate, snow cover and streamflow are closely connected, and their interactions
in high mountain terrains will impact the availability of water for downstream
populations. In arid or semi-arid environment, such the Mediterranean, societies
have adapted to an irregular availability of water (as a consequence of the high
inter-and intra-annual variability of precipitation and temperature) mainly through
the construction of dams in mountain valleys for storing water during the periods of
water excess, and its release during the high demand and/or low water availability
seasons (which are usually coincident). The rapid changes that mountain flows are
experiencing, not only due to climate change/variability but also due to land use
shifts through afforestation/deforestation and natural land cover expansion (Poyatos
et al. 2003), makes it necessary to adapt the water consumption strategies in areas
downstream including the management of dams located in mountain valleys
(López-Moreno et al. 2004). The assessment of processes involving climate, snow,
and hydrology by scientists, at high elevations, must be therefore a key step in
planning conservation strategies for mountain territories.
The Pyrenees, located in the transition of Atlantic and Mediterranean climate
influences, constitute a paradigmatic example of mountains undergoing rapid
changes in environmental conditions, with a potential impact on the availability of
water resources for downstream populations. Water availability downstream is
highly related to the timing of snow accumulation and snowmelt (López-Moreno
306
E. Morán-Tejeda et al.
Amongst many other ecological functions, mountains play a major role as freshwater reservoirs, this being especially relevant in arid and semi-arid regions
(Viviroli et al. 2007). Either in the form of aquifers, lakes, snow or ice cover, the
water stored by mountains often represents the principal source of water for most
populated areas that are usually located downstream. Thus any process involving
changes in the hydrological cycle in the mountains, e.g. in climate variables, land
cover, soil properties, or snow cover (Arnell 1999; Foley et al. 2005; Stewart et al.
2005; Bormann et al. 2007; López-Moreno et al. 2011), will have an impact on
water availability downstream. Recent observed worldwide warming is inducing
environmental changes in high mountains related to their capacity for storing water,
including a decrease in the accumulation and accelerated melting of snow, the
consequent reduction in the duration of the snowpack, the receding of glaciers and
the loss of permafrost (Barnett et al. 2005; Lemke et al. 2007; Adam et al. 2009).
Mountains and the process of snow accumulation-melting are hotspots for climate
change impacts (Beniston 2003), due to the high sensitivity of the snow cover to
seasonal temperatures, especially in low-to-middle elevation sites (Morán-Tejeda
et al. 2013). Streamflow, as the ultimate output of mountain systems, will reflect
these environmental signals by changing its timing and magnitude, and thus
becomes not only a vital resource for populations, but also an important indicator of
environmental changes, including global warming, for scientific research.
Climate, snow cover and streamflow are closely connected, and their interactions
in high mountain terrains will impact the availability of water for downstream
populations. In arid or semi-arid environment, such the Mediterranean, societies
have adapted to an irregular availability of water (as a consequence of the high
inter-and intra-annual variability of precipitation and temperature) mainly through
the construction of dams in mountain valleys for storing water during the periods of
water excess, and its release during the high demand and/or low water availability
seasons (which are usually coincident). The rapid changes that mountain flows are
experiencing, not only due to climate change/variability but also due to land use
shifts through afforestation/deforestation and natural land cover expansion (Poyatos
et al. 2003), makes it necessary to adapt the water consumption strategies in areas
downstream including the management of dams located in mountain valleys
(López-Moreno et al. 2004). The assessment of processes involving climate, snow,
and hydrology by scientists, at high elevations, must be therefore a key step in
planning conservation strategies for mountain territories.
The Pyrenees, located in the transition of Atlantic and Mediterranean climate
influences, constitute a paradigmatic example of mountains undergoing rapid
changes in environmental conditions, with a potential impact on the availability of
water resources for downstream populations. Water availability downstream is
highly related to the timing of snow accumulation and snowmelt (López-Moreno
306
E. Morán-Tejeda et al.