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Date: Fri, 23 Mar 2001 12:19:17 -0800
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From: Lori Pottinger <lori@irn.org>
Subject: Fwd: Methodology developed for assessing climate/LS
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>From: Richard Sherman <rsherman@earthlife.org.za>
>
>Subject: Methodology developed for assessing climate
>Date: Fri, 23 Mar 2001 15:35:38 +0200
>
>
>SA WATERBULLETIN
>Volume 23 No 4 July/August 1997
>Methodology developed for assessing climate
>Results from a research project funded by the Water Research Commission
>(WRC) have demonstrated that an "empirical downscaling technique" based on
>the use of neural nets is a valuable approach toward creating more robust
>climate change scenarios at suitable spatial and temporal scales, for use by
>South African climate change impacts researchers.
>According to the researcher, BC Hewitson, of the Department of Environmental
>and Geographical Science at the University of Cape Town, the methodology
>offers a technique by which researchers may derive local climate scenarios
>from global-scale scenarios generated using general circulation models. It
>represents a significant advance over the climate change data currently
>available from other sources.
>Further results based on the methodology should in the future be of direct
>interest to South African researchers in a wide spectrum of disciplines.
>However, "while the initial scenarios developed here are consistent with
>broad expectations of climate change impacts, they should not be considered
>too definitive as further work is needed to develop confidence levels for
>the scenarios."
>The results are summarised in a final report entitled A methodology for
>developing regional climate change scenarios from general circulation models
>(WRC Report 594/1/97). Copies of the report are available free of charge
>from the Water Research Commission, PO Box 824, Pretoria 0001. E-mail order
>address: tineke@ wrc.org.za <mailto:tineke@wrc.org.za>. (Overseas price: US$
>15, via surface mail.)
>
>South Africa's climate is subject to high inter-annual variability and
>presents significant vulnerabilities in the face of probable global climate
>change. Regional impacts from global changes are most likely to be manifest
>in the hydrological aspects which will impact water resources and water
>dependent infrastructures most strongly. In the face of the long lead times
>required for planning and policy development it is vital that an accurate
>understanding be developed of the probable regional consequences of global
>environmental change for the next five to ten decades.
>The most viable tools for such investigations are general circulation models
>which attempt to simulate the global geophysical system encompassing the
>land, ocean and atmosphere. However, while general circulation models manage
>to simulate global-scale processes with considerable success, the models are
>also relatively coarse resolution tools and fail to resolve the detail of
>regional climate variability, especially with regard to hydrological
>variables. It is particularly at these higher resolution scales, which the
>general circulation model fails to capture adequately, that climate change
>information is most needed.
>This shortcoming may be addressed through the use of "downscaling" which
>utilises the dependence of local-scale climates on the large scale
>circulation to derive regional information. In essence, downscaling uses
>observed data to derive relationships between the larger scale atmospheric
>circulation and local climate parameters. These relationships may then be
>used in conjunction with the more viable large scale circulation from
>general circulation models to derive local climate information based on the
>general circulation model simulation of atmospheric circulation.
>OBJECTIVES
>The primary aim of the project was to derive regional scenarios for global
>climate change impacts on regional precipitation and temperature over South
>Africa as a consequence of anthropogenic increases of atmospheric carbon
>dioxide. In doing so, three objectives were targeted:
>* To validate general circulation model simulations of atmospheric
>controls on regional precipitation and temperature over South Africa;
>* To develop a new non-linear methodology for cross-scale climate
>relationships;
>* To develop quantified estimates of the regional changes for use as
>input to hydrological and agricultural models.
>RESULTS
>The investigation has led to the development of a new downscaling procedure
>for South Africa based on artificial neural nets to derive relationships
>between circulation and local precipitation and temperature on a one degree
>(1?) latitude-longitude grid. These derived relationships were evaluated for
>accuracy, and demonstrated that the relationships do successfully capture
>both short and long term variability in the regional climates as a function
>of the larger scale circulation. For both the downscaled precipitation and
>downscaled temperatures, the nature of the near-daily event is well
>captured, as well as the seasonal timing and amplitude for both variables.
>General circulation models' circulation data were then evaluated for
>validity over South Africa using a principal components analysis technique.
>The circulation in terms of the spatial distribution of variance was shown
>to be a reasonable reflection of present day circulation. The artificial
>neural nets relationships between circulation and local climate were
>subsequently applied to the general circulation models' daily circulation
>data from a simulation of present day conditions and the regional climates
>derived.
>The regional climates generated by the general circulation model's
>circulation were shown to demonstrate a high degree of similarity to the
>observed regional climates and further indicates that the general
>circulation model reasonably simulates the large scale circulation forcing
>over South Africa. The relationships were then applied to data from a
>general circulation model simulation of future conditions under doubled
>atmospheric carbon dioxide, and the results differenced from the present day
>simulation to generate the carbon dioxide induced changes in regional
>climates.
>The primary results of consequence for climate change impacts indicate that,
>as a function of changes in the general circulation models' circulation
>forcing, there are reductions in the regional summer precipitation over the
>summer rainfall region extending from the east coast through to the central
>and northern regions of the country. These reductions are of the order of a
>ten to fifteen per cent decrease in mean monthly precipitation. However, the
>results are preliminary, based on only one model, and should be used only as
>an initial possible indication of change.
>
>Richard Sherman
>Research and Policy Coordinator
>Sustainable Energy and Climate Change Partnership
>Earthlife Africa Johannesburg
>P.O.Box 11383 Johannesburg 2000, South Africa
>Phone: +27 11 339 3662
>Fax: +27 11 339 3270
>Cell: 082 464 1742
>www.earthlife.org.za
>
>
--
::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
Lori Pottinger, Director, Southern Africa Program,
and Editor, World Rivers Review
International Rivers Network <'})))>><
1847 Berkeley Way, Berkeley, California 94703, USA
Tel. (510) 848 1155 Fax (510) 848 1008
http://www.irn.org
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