Geoscience Reference
In-Depth Information
Australia are predicted to have an increase in annual
runoff by up to 25 per cent, Tasmania a 10 per cent
increase, and a 35 per cent decrease in South
Australia, by 2030. The uncertainty of this type of
prediction is illustrated by south-east Australia
where there are possible runoff changes of ±20 per
cent (Chiew et al ., 1995). Similarly, Kaleris et al .
(2001) attempted to model the impacts of future
climate change on rivers in Greece but concluded
that the 'error of the model is significantly larger
than climate change impacts' and therefore no firm
conclusions could be made. Overall it is difficult to
make specific predictions for changes in hydrology
as the feedback mechanisms within climate change
are not properly understood.
hydrologists over the last fifty or more years. Issues
of land use change affecting hydrology include
increasing urbanisation (see pp. 168-173), chang-
ing vegetation cover, land drainage and changing
agricultural practices leading to salination.
Vegetation change
In Chapter 3 a Case Study showed the effect that
trees have on evaporation and interception rates.
This is a hydrological impact of vegetation cover
change, a subject that Bosch and Hewlett (1982)
review in considerable depth. In general Bosch and
Hewlett conclude that the greater the amount of
deforestation the larger the subsequent stream-
flows will be, but the actual amount is dependent
on the vegetation type and precipitation amount.
This is illustrated by the data in Table 8.4. In the
Australian study of Crockford and Richardson
(1990) the large range of values are from different
Change in land use
The implications of land use change for hydrology
has been an area of intense interest to research
Table 8.4 The amount of interception loss (or similar - see note below) for various canopies as
detected in several studies
Canopy cover
Interception loss
Source
Eucalypt forest (Australia)
5-26% per rainfall event
Crockford and Richardson
(1990)
Pine forest (Australia)
6-52% per event
Crockford and Richardson
(1990)
Oak stand (Denmark)
15% of summer rainfall
Rasmussen and Rasmussen
(1984)
Amazonian rainforest
9% of annual
Lloyd et al . (1988)
Sitka spruce (Lancashire, UK)
38% of annual precipitation*
Law (1956)
Sitka spruce (Wales)
30% of annual precipitation*
Kirby et al . (1991)
Grassland (Wales)
18% of annual precipitation*
Kirby et al . (1991)
Young Douglas fir (New
27% of 7-month summer/
Zealand) (closed canopy)
autumn period
Fahey et al . (2001)
Mature Douglas fir (NZ)
24% of 7-month summer/
Fahey et al . (2001)
autumn period
Young Pinus radiata (NZ)
19% of 7-month summer/
Fahey et al . (2001)
(closed canopy)
autumn period
Note : *The figures denoted with an asterisk are actually evapotranspiration values rather than absolute
interception loss, leading to higher values.
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