Outcomes of synthesis - Runoff Prediction in Ungauged Basins: Synthesis across Processes, Places and Scales - page 363

maximum flood peaks. For these reasons, seasonality
forms a strong basis for catchment classification in several
regions of the world.
The connection across all signatures can be best illus-
trated by the example of Austria. Figure 12.2 presents
snapshots of the spatial patterns of the mean values of the
six runoff signatures: mean annual runoff ( Chapter 5 ),
timing of runoff maxima ( Chapter 6 ), slope of the flow
duration curve ( Chapter 7 ), Q 95 as a measure of low flow
( Chapter 8 ), Q 5 as an indicator of high flow ( Chapter 9 ),
and an integral time scale, used as a measure of runoff
temporal variability ( Chapter 10 ). They represent different
aspects of the full range of runoff variability across Aus-
tria, through spotlights that focus on particular aspects (or
time scales) of that variability.
In Austria, the spatial patterns observed in different flow
signatures can be traced back to a fairly small subset of key
processes, particularly the role of snow, the absolute
volume of precipitation, the seasonality of precipitation
and evapotranspiration, and the typical runoff dynamics
(slow versus flashy).
For example, snow dynamics are responsible for
summer maxima in runoff in western Austria, for the steep
flow duration curves associated with runoff events in these
areas, for the emergence of winter minima in low flows,
and finally for the long integral time scales of runoff peaks
(Blöschl, 1996 ). The large volumes of runoff in western
Austria, however, relate not to snow but to the effects of
orographic lifting of north-westerly airflows at the rim of
the Alps, leading to precipitation rates of more than 2000
mm/yr. Precipitation is lowest in the lowlands of the east,
and the contrast with the Alps is exaggerated by higher
evaporation in the east. The role of evaporation in the east
is in-phase with precipitation maxima in summer, leading
to runoff maxima in spring, and summer

12.2 Synthesis across processes, places and scales
12.2.1 Synthesis across processes
Signatures are connected
Runoff signatures, collectively, reveal the nature of runoff
variability in time and space. They are emergent properties
of the hydrological functioning of catchments. Each signa-
ture reveals a different aspect of the catchment function.
When juxtaposed with corresponding patterns of climate
inputs and catchment characteristics, runoff signatures can
help to explain the causes of hydrological variability and
may thus assist with predictions. Since different aspects of
climate and catchment characteristics control different sig-
natures, a hierarchical exploration of these signatures helps
to decipher these controls better than direct comparison or
curve fitting of complex hydrology models against
observed time series at one or more places.
The different chapters of the topic: 5 (annual), 6 (sea-
sonal), 7 (flow duration curve, daily), 8 (low flows),
9 (floods) and 10 (runoff hydrograph), focus on runoff
variability on different temporal scales. The emergent con-
trols or dominant drivers of this variability also change with
the temporal scale of interest. In Chapter 5 , annual runoff is
clearly and predominantly governed by the relative avail-
ability of water and energy, as reflected in the Budyko
curve. Other factors that alter mean annual runoff, such as
the seasonality of precipitation and potential evaporation,
and vegetation cover or soil type/depth, produce mostly
secondary effects. When focusing on seasonal runoff, how-
ever, the dominant control becomes seasonality of precipi-
tation and potential evaporation and storage in the soils,
groundwater and as snow and ice. When it comes to the
flow duration curve in Chapter 7 , the controls become more
complex: apart from temperature and seasonality, which
control the middle part of the flow duration curve, low flows
are predominantly governed by recharge and geology, and
high flows are governed by storminess (event) characteris-
tics of precipitation as well as antecedent conditions. These
factors, and others, impact the complete hydrograph, as
discussed in Chapter 10 .
The discussion in Chapters 5 through 10 also brings out
the interconnectedness of the runoff signatures. In spite of
the fact that each reflects a distinct characteristic of runoff
variability there are overlaps, to the extent that understand-
ing or prediction of one signature can contribute to the
same for other signatures. For example, relative seasonality
of water and energy inputs contributes to both the mean
and inter-annual variability of annual runoff. Seasonality
of runoff largely structures the within-year variability cap-
tured in the flow duration curve, and governs the magni-
tude of its slope. Seasonality, through its impact on both
precipitation inputs and the antecedent soil wetness, is a
key factor

low flow

conditions.
The spatial pattern of floods is also closely related to the
spatial pattern of annual rainfall. This arises from three
causes, direct rainfall input at the event scale, antecedent
soil moisture, and landform

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hydrology feedbacks, which
produce more efficient drainage networks in high rainfall
areas (Blöschl and Merz, 2008a , 2010 ). Otherwise, the role
of the catchment morphology and geology in shaping
hydrological signatures is most obvious in the flow dur-
ation curve and the runoff hydrograph. Aside from snow-
dominated areas, flashy locations are associated with con-
vective precipitation and rapidly draining soils, arising due
to the co-evolution of climate, landscape and soils (Gaàl
et al., 2012 ); in these regions the integral time scale of
runoff is short, and the duration curves are flat. Slow
dynamics in the hydrograph also arise in regions with
highly pervious geology (as in the south of Austria), and
are also reflected in large low flows and small floods.

in the magnitude and timing of annual