Civil Engineering Reference
In-Depth Information
9% in throughflow, and 13% in underground runoffs. Impacts will
be greater in the summer months and problems aggravated in the dry
months.
This can have devastating effects on providing a reliable supply particu-
larly in arid and semi-arid areas. Furthermore, less runoff combined with
higher temperatures can affect river water quality, e.g. through increases in
blue-green algae.
Recent work by Australia's Commonwealth Scientific and Industrial
Research Organisation (CSIRO) (see Chiew
et al.
2008) considered a range
of future inflow scenarios for water resources in the Murray-Darling Basin as
follows:
O
a continuation of the climate of the past 112 years
O
a continuation of the climate of the recent 10 years (very dry)
O
projections of climate in 2030 taking account of global warming.
Global warming scenarios were determined using data from a set of 15
internationally recognised global climate models, which simulate the effect
of rising levels of greenhouse gases in the atmosphere on regional rainfall
patterns. Data from three different emission scenarios (low, medium and high
emissions) for each model were used, giving in total 45 data sets. From these
scenarios, three were selected as representing upper, lower and median levels
for possible average future inflows. This approach was intended to encompass
uncertainty in both future emission levels and in the models themselves.
Derived future climatic statistics were then imposed on 112 years of historic
climatic data to produce adjusted datasets for the purpose of assessing risks
and comparing management scenarios.
The CSIRO then combined these climatic scenarios with water resource
models to simulate resource behaviour under different development scenarios
to provide information on associated flows and availability of water for
extraction and watering of environmental assets. See Box 5.1 for an example
of how this information was used in the Northern Victorian part of the
Murray Darling Basin.
Non-flow data can also be used to improve understanding of possible future
flows by extending knowledge about flows in the past, thereby capturing
more information about long-term climatic cycles. For example, the historic
flow record for the Oldman River in Alberta Canada was extended back 628
years using tree ring data, revealing greater inter annual and inter decadal
variability than the data from river gauges over the last 110 years, including
more severe drought years in the early 1700s and longer periods of low flow
in the 1840s to 1870s (Corkal
et al.
2011).
Scenario development is not without challenges. Models are only as reliable
as the data and need to be validated. Decisions need to be made about the
time and spatial scales for scenario development - between 5 to 20 years, a
