Prediction of seasonal runoff in ungauged basins - Runoff Prediction in Ungauged Basins: Synthesis across Processes, Places and Scales - page 107

Figure 6.5. Annual cycle of precipitation and water storage components for large river basins; mean monthly values for the period
1961 95. Dominance of snow storage in cold regions and soil and groundwater storage in temperate and tropical regions is shown. From

Güntner et al.( 2007 ).

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summer, generally following energy availability closely
(Röthlisberger and Lang, 1987 ). This contrasts with
purely snowmelt-driven catchments, where the loss of
seasonal snowpack trades off against energy availability,
often leading to peak runoff

fluctuations in total storage range from around 35% in
the Amazon to around 60% in the Oranje and Niger
Rivers. The contribution of individual storage compart-
ments to total storage variability differs between the cli-
mate zones. Snow storage dominates in cold and polar
regions (e.g., the Yenisei River), and soil water and
groundwater dominate in the temperate and tropical zone.
Groundwater storage changes tend to be expressed at
inter-annual rather than seasonal levels due to the longer
residence times in groundwater. Seasonal groundwater
recharge, however, is often important in sustaining low
flow phases (see e.g., Wood et al., 2001 ).
To support a process-based explanation of the link
between the seasonal pattern of storage mechanisms within
soil water and groundwater stores and the seasonal pattern
of runoff generation, we use the classic example from the
Havel River first presented by Wundt ( 1953 )( Figure 6.6 ).
During winter, precipitation exceeds evaporation, allowing
an accumulation of soil and groundwater storage, and
(eventually) increased runoff generation. The stored water
sustains runoff during spring and summer when evapor-
ation exceeds precipitation, but is depleted during this
period. The net result is a mild seasonality in runoff, which

in late spring or early

summer.

Catchment processes: storage in soil and groundwater
In contrast to snow and glacial processes, storage of water
within the catchment s soils and aquifers does not have a

directly seasonal component, but tends to reflect a
response to the seasonality of water input via precipita-
tion and evaporative losses via transpiration. Baseflow is
usually proportional to storage, so the seasonality of
storage helps to shape the flow regime. Water storage in
soils and aquifers is important due to its role in supplying
the evaporative demand of plants, and providing a reser-
voir, often used to supply human extractive uses. Sea-
sonal variations represent the dominant time variable
signal of water storage change (Güntner et al., 2007 ).
Figure 6.5 shows the annual cycle of variability of pre-
cipitation and various components of water storage for six
large river basins around the world. The annual

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