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Modelling the influence of vegetation, soil moisture and aerosols on early summer Southern African climate
Expanded Title:Little is currently known regarding global and regional controls of the early part of the rainfall season. An enhanced understanding of the controls of early-season rainfall characteristics are required to enable the design of new forecasting methodologies, which in turn may offer practical benefits to water managers and under-served members of the South African population e.g. subsistence farmers. New forecasting methodologies will require knowledge of which antecedent conditions (vegetation, aerosols, soil moisture and SST) are important and be able to use this information to predict early-season rainfall, given likely non-linear interactions. Such knowledge will also enable a clearer assessment of the impact of other human-induced changes (besides changing greenhouse gas levels), currently unknown factors in the development of scenarios of regional climate change. This project focussed on the links between early season (September-January) rainfall and local antecedent conditions of vegetation, soil moisture and atmospheric aerosols. The primary reasons for choosing these foci were: a) early season rainfall is hard to forecast, yet it’s interannual variability can have important impacts in many sectors; b) these antecedent conditions to date have received little attention and are currently assumed to have a small influence on forecasts at a range of timescales. The majority of the project has focussed on using Regional Climate Models (RCMs) to simulate the impact of changes in these antecedent conditions on rainfall. Given this is a computationally demanding task and that it was necessary to use several different RCMs (due to structural constraints some RCMs cannot be used for simulating particular changes), the modelling requirements of this project were high and took up the majority of the available time and work. The RCMs used in this work include the Weather Research and Forecasting (WRF) model, the Mesoscale Model 5 (MM5) and the Regional Climate Model 3 (RegCM3). In all experiments the resulting changes in rainfall are heterogeneous and tied to changes in the atmospheric circulation, rather than a direct consequence of changes in the local antecedent conditions. Changes in atmospheric circulation induce changes in convergence/divergence and consequently rainfall. Changes in surface temperature, however, were clearly tied to changes in latent/sensible heat fluxes with clear links to changes in surface properties and energy budget. There is a need to develop a forecast methodology that can use observed changes in these antecedent conditions to improve current forecasts. This was not achieved in this project but a way in which it could be achieved within the current forecast framework at CSAG and should be a goal within any future projects is suggested.
Date Published:01/02/2011
Document Type:Research Report
Document Subjects:Agricultural Water - Agro forestry, Ecosystem - Biodiversity protection, Ecosystem - Biomonitoring, R & D - Research capacity
Document Keywords:Policy and regulation, Guidelines, Environment, Municipality, Climate, Water Quality
Document Format:Report
Document File Type:pdf
Research Report Type:Standard
WRC Report No:1681/1/10
ISBN No:9781770059764
Authors:Tadross M; Oliveira I ; Mdoka M; Tummon F; Maure G; MacKellar N; Browne N; Crespo O; Hachigonta S; Hewitson B
Project Leader:Tadross M
Project No:K5/1681
Organizations:Department of Environmental and Geographical Science,
Document Size:4 506 KB
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