No abstract

Evidence is provided of the successful application of a single atmospheric model code at time scales ranging from shortrange weather forecasting through to projections of future climate change, and at spatial scales that vary from relatively low-resolution global simulations, to ultra-high resolution simulations at the micro-scale. The model used for these experiments is a variable-resolution global atmospheric model, the conformal-cubic atmospheric model (CCAM). It is shown that CCAM may be used to obtain plausible projections of future climate change, as well as skilful forecasts at the seasonal and short-range time scales, over the Southern African region. The model is additionally applied for extended simulations of present-day climate at spatial scales ranging from global simulations at relatively low horizontal resolution, to the micro-scale at ultra-high (1 km) resolution. Applying the atmospheric model at the shorter time scales provides the opportunity to test its physical parameterisation schemes and its response to fundamental forcing mechanisms (e.g. ENSO). The existing skill levels at the shorter time scales enhance the confidence in the model projections of future climate change, whilst the related verification studies indicate opportunities for future model improvement.

Challenges facing the livestock sector towards 2050 and the changes and management considerations required to maintain sustainability are discussed. Major challenges are associated with climate change and the environmental impact of the sector. Southern Africa is predicted to become drier and the average temperature may rise by 1.5 ºC to 2 ºC. Livestock CH 4 emissions are 1330 Gg/year, with enteric fermentation contributing 95%. For commercial production of beef and milk, CH 4 estimates are at the upper half of life cycle assessments of 14 -32 kg CO 2 e/kg beef and 0.84 -1.4 kg CO 2 e/kg milk recorded for developed countries. The water footprint depends on production system and efficiency. Global and South African water use estimates for red meat production vary from 80 to 540 L/kg meat. In dairy plants the water usage to process the same product may vary by more than 100%, suggesting scope for improvement. Although animal welfare in South Africa is supported by the Livestock Welfare Coordinating Committee and adherence codes, humane treatment of animals is more difficult to maintain in intensively-housed production systems. Livestock production in communal and small scale sectors requires rapid commercialisation to relieve poverty and contribute to gross domestic product. This requires partnerships, major inputs and paradigm shifts. Input costs including labour increase faster than commodity prices, the concern with labour costs being the impact on employment rates. Efficiency of production should be on par with competitors if the livestock sector is to compete on domestic and export markets. The poultry industry is on par, but rising feed costs, disease and subsidized imports are major concerns. Efficiency in the other industries as measured by off-take percentage is generally lower than competitors, a major reason being lower reproductive rates. In this context, the amount of feed, water and CH 4 /kg beef can be reduced by more than 20% if calving rate increases by 20 percentage points. Effective management of rangeland is critical, even more so because of climate change. Livestock production is only marginally competitive and therefore vulnerable to deregulation and trade liberalization. To increase competitiveness exports should increase markedly. For participation in world trade, controlled and notifiable diseases remain a risk. Associated risks are zoonosis and microbial resistance to antibiotics. Stock theft and predation are major concerns. Farmers should employ bio-security measures to ensure the supply of safe products to the consumer. Government and the livestock industries will have to show a clear and strong commitment to address the challenges and opportunities to ensure sustainability of the livestock sector.________________________________________________________________________________

Explorations of the impact of climate change on potential potato yields were obtained by downscaling the projections of six different coupled climate models to high spatial resolution over southern Africa. The simulations of daily maximum and minimum temperatures, precipitation, wind speed, and solar radiation were used as input to run the crop growth model LINTUL-Potato. Pixels representative for potato growing areas were selected for four globally occurring agro-ecosystems: rainy and dry winter and summer crops. The simulated inter-annual variability is much greater for rainfall than for temperature. Reference evapotranspiration and radiation are projected to hardly decline over the 90-year period, whilst temperatures are projected to rise significantly by about 1.9°C. From literature, it was found that radiation use efficiency of potato increased with elevated CO 2 concentrations by almost 0.002 gMJ −1 ppm −1 . This ratio was used to calculate the CO 2 effect on yields between 1960 and 2050, when CO 2 concentration increases from 315 to 550 ppm. Within this range, evapotranspiration by the potato crop was reduced by about 13% according to literature. Simulated yield increase was strongest in the Mediterraneantype winter crop (+37%) and least under Mediterranean summer (+12%) and relatively warm winter conditions (+14%) closer to the equator. Water use efficiency also increased most in the cool rainy Mediterranean winter (+45%) and least so in the winter crop closer to the equator (+14%). It is concluded from the simulations that for all four agro-ecosystems possible negative effects of rising temperatures and reduced availability of water for potato are more than compensated for by the positive effect of increased CO 2 levels on water use efficiency and crop productivity.