Geoscience Reference
In-Depth Information
cally different hydrology, topography and political economy. Yet some water issues
are best dealt with at regional or national scales, particularly where they affect
public health. This governance-scale conundrum has long beset environmental geog-
raphers working on water resources, who have been infl uential in public policy
debates on these issues.
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Research in hydrology and physical geography faces similar conceptual problems.
Given that water is a fl ow resource, any study of water must deal simultaneously
with multiple (and nested) spatial and temporal scales. Given a high degree of space-
time variability, how can we make generalisable statements (or derive theoretical
models) about the behaviour and evolution of hydrological systems? And given this
high degree of variability and scale-interdependence, at what scale(s) is water best
studied?
The problem of scaling (both upscaling and downscaling) is thus an important
one in the study of water, both because of the interrelatedness of scales (the hydro-
logical cycle, the global climate system and a local watershed) and because of a high
spatial and temporal variability of key variables (soil moisture, precipitation, land
cover and land use). Hydrologists need to make useful statements about variability
in order to compare, generalise, and extrapolate results, but scalar change compli-
cates this task, because variability changes as scale changes (Culling and Datko,
1987; Woods, 2005). This 'scaled variance' phenomenon is of critical importance
to hydrology because
'virtually any quantitative approach to [the problem of vari-
ability] requires the selection of a limited set of spatial and temporal scales . . . [which]
has a major infl uence on which aspects of this hydrological variability are perceived'
(Bloschl, 2005).
Taking this 'scaled variance' phenomenon into account has, in fact, led environ-
mental geographers to groundbreaking research on water-related topics, such as
urban micro-meteorology and urban climatology. Urban climatology, urban hydrol-
ogy and the urban water balance are typical of the sorts of problems studied by
physical geographers, as they are characterised by fi ner spatial resolution than
atmospheric scientists, tight feedbacks between human and natural systems, and
important management and policy implications. The legitimacy for this research
within geography stems in part from a broader tradition of studying 'human impacts
on the environment' (Clark et al., 1990; Kasperson et al. 1995; Goudie 2000).
Urban climatologists and hydrologists have demonstrated that the urban scale is
markedly different from other scales and locales due to a high degree of alteration
of the landscape, which signifi cantly changes the water balance (Grimmond and
Oke 1986; Grimmond et al., 1986; Aronica and Lanza 2005).
Specifi cally, urban runoff is greater than rural runoff and the peak in runoff
following precipitation events happens much more quickly (due to a lower pro-
portion of permeable plant and ground cover). A high degree of imperviousness
results in lower evaporation and transpiration. And, since human water use has
diurnal and seasonal peaks, urban water bodies from which water is removed and
to which effl uent experience (often signifi cantly) altered water quality. These changes
in local meteorological conditions may be further impacted by the 'urban heat
island' effect, the study of which was fi rst scientifi cally systematised by geographer
Tim Oke (Oke 1982; Roth et al., 1989). Many, if not all, of these impacts would
be obscured if analysis was conducted at a regional watershed scale. The choice
of scale, in short, is of crucial importance to an assessment of environmental
impacts.
