Geography Reference
In-Depth Information
Figure 6.4. Schematic of the
influence of precipitation and snow
cover on the shape of the runoff
regime. Blue lines represent the
seasonal runoff regime without the
effect of snow; grey lines represent
the seasonal runoff regime with the
effect of snow storage and melting.
After Grimm ( 1968 ).
runoff seasonality in different places and at different
times (Cloke and Hannah, 2011 ). Better quantification
of the inter-connections between climate, atmosphere,
land and surface hydrology is particularly important
(Kingston et al., 2009 ). This research lies in the realm
of hydrometeorology and climate science, and is not
treated extensively here.
region, such as Austria and Slovakia, one sees that in the
snow-dominated mountainous parts of the region the
seasonality is very stable even at the decadal scale, while
the variability is higher in the hilly regions or the low-
lands, where many mechanisms (e.g., convective vs.
synoptic precipitation) may be equally important (Para-
jka et al., 2008 , 2009 a). In general, frozen water storage
affects the flow regimes of rivers that drain mountainous
regions (e.g., Alps, Himalayas, Rockies, Andes), polar
regions (particularly in the northern hemisphere), and
regions with a continental climate (e.g., the interiors of
Russia and North America).
A generalised example of the interaction between sea-
sonality in precipitation and the role of snow cover, as
revealed in the seasonal flow regimes of European rivers,
is presented in Figure 6.4 (Grimm, 1968 ). The flow
regime in the first row on the left depicts a catchment
from the temperate climate zone with equal seasonal
rainfall distribution, no snowfall and high evaporation
rates during the summer. The varied flow regimes along
the horizontal axis result from different patterns of sea-
sonal distribution of precipitation, while variation along
the vertical axis arises due to the influence of snow.
While the input of precipitation and energy (net radiation)
determine the basic pattern of seasonal runoff, storage
and snowmelt at the local level strongly modify the flow
regimes.
Glaciers have a major influence on river flow regimes
(e.g., Hannah et al., 1999 , 2000 , 2005 ). As little as 10%
ice cover in a catchment can significantly affect river runoff
(Fountain and Tangborn, 1985 ) (see also Figure 6.16 ).
Glacier-driven catchments have a characteristic sea-
sonal
Catchment processes: storage in snow, ice and glaciers
As mentioned above, the role of storage has a significant
impact on seasonality in runoff, strongly modulating the
seasonality in climate. In this section we separate the
effects of storage in snow and ice (dominant in cold
regions), and storage in soils and aquifers (common to all
regions), as they have different manifestations in seasonal
flow regimes.
In cold regions, storage processes related to the accu-
mulation and melting of the snowpack, ice and glaciers
drive the strong seasonal runoff patterns. These effects
are clearly illustrated in the comparison of the regimes of
the Lafnitz and Lech Rivers in Austria presented earlier
( Figure 6.3 ). The lowland Lafnitz River has low storage
of frozen precipitation in its catchment, and therefore a
generally flat flow regime. The Lech River, however,
experiences pronounced seasonal snow accumulation
and a well-defined snowmelt period, generating a highly
seasonal flow regime. The relatively low between-year
runoff variability in the Lech River reflects the low
between-year variability in energy input (the regular
seasonality that drives snow accumulation and melt).
For the lowland Lafnitz River, the randomness of pre-
cipitation plays the dominant role in determining the
between-year runoff variability. If one considers a larger
runoff pattern of peak glacier-melt
in mid
-
late
 
Search WWH ::




Custom Search