Overview of key climate messages from Zimbabwe drawn from multiple sources of evidence
Past climate variability
High variability, frequent drought years and flood events
Historical rainfall records (CRU data)
Past climate trends
Increasing temperatures (~0.1°C/decade)
No conclusive changes in precipitation
Historical temperature and rainfall records (CRU data)
Future climate trends
Increasing temperatures of around 2.5°C by the 2050s
Possible decrease in rainfall particularly during the onset stage of the rainy season (Sep- Nov)
CMIP3 GCM multi-model projections (for SRES A2 emissions scenario) and CSAG downscaled projections available in CIP
Future climate trends
We now look more closely at the projections of future climate trends in Zimbabwe using 10 of the 21 available Global Climate Models (GCMs) used in the IPCC Fourth Assessment Report and suggest possible impacts associated with such changes. To consider local specificities, we look at finer scale projections for a station in Rusape, a high altitude location south east of Harare, and Messina, which lies near the southern border between Zimbabwe and South Africa. While not actually within Zimbabwe, projections for Messina are likely to be similar to places in the southern parts of Zimbabwe. Having downscaled projections for more locations would be preferable, but this requires access to long-term records of historical climate observations, which are currently not available.
But remember, while projections of future climate change are important, they should not be seen as the starting point of the adaptation process. Rather, adaptation efforts should focus on those places and people most vulnerable to, and at risk from, current climate conditions – so do go and look more closely at analyses of observed records (e.g. the CRU data set) and how the range of conditions currently experienced impact on different people. While working to address current climate risks we should in the process be building local capacities to continue monitoring and adapting as these climate conditions continue to change into the future.
Confidence of the projection
2 – 2.75o C temperature increase by the middle of the century (the period 2046-2065)
Changes in crop yields
Changes in forest biomes
Decreased supply and quality of water
Melting of tar on roads
There is a high level of agreement between the projections of temperature generated by the different Globa climate Models; therefore we can have high confidence in the resulting information. Projected changes are in the range of 2°C to 2.75°C across the different models for the SRES A2 emissions scenario (estimated global emissions in a world of independently operating nations, a growing global population and regionally orientated economic development). Greater increases are expected across the western parts of the country.
Increases in temperature may change the areas in which various crops can be grown and decrease crop productivity relative to current levels. An increase in temperature may make Zimbabwe more suitable for forest biomes found in the subtropical climates than the temperate climates that currently exist. Higher temperatures affect soil moisture content, thereby altering the supply and quality of water, as well as the demand for agriculture and domestic use, particularly in the rural areas. Higher temperatures may also lead to tar melting in densely built up urban areas, disrupting mobility and increasing the cost of maintaining public infrastructure.
Confidence of the projection
Decrease in early season rainfall in Sept to Nov and later onset of Dec-Jan rainy season is expected by the middle of the century (the period 2046-2065)
Changing crop patterns
Increased erosion loss of soil water retention
Wells and boreholes dry up
Decreased water availability leads to poor sanitation and is associated health impacts
Disruption to hydroelectric power
Projections of rainfall by Global Climate Model (GCM) show very little agreement and so we have low confidence in the resulting information. Some models project increases in rainfall in the December – February wet season while others project drier conditions. The only pattern with some consistency is a decrease in early season rainfall in September to November suggesting a later start to the rainy season in the future. Finer scale projections for Rusape and Messina support this conclusion. Data from Messina also shows some signs of drying throughout the rainy season in the future.
Temperatures in Zimbabwe begin to increase during September-November so when the rainfall season starts later it has already been preceded by several months of hot dry conditions rather than the cooler conditions that precede the current rainy season. This can have important impacts on field preparation, crop growth phases and ripening, as well as water resource management. Less rain in the early part of what has historically been the rainy season rainfall may lead to loss of soil water retention, in turn leading to increases in erosion. Rural wells and boreholes may dry up, undermining sanitation and threatening human health. Urban water supplies may be severely limited and hydroelectric power generation may be interrupted.
Important source of uncertainty
An important source of uncertainty in this region is the impact of global warming on the El Nino Southern Oscillation (ENSO) phenomenon. ENSO has an impact on variation in the regional climate between years. While there are some early suggestions that global warming will tend to produce more frequent El Nino conditions, many models do not yet correctly capture ENSO. Research is ongoing in this area and it is possible that future projection sets will include more models that are able to correctly capture and represent the influence of ENSO.
This climate analysis was developed by a team of researchers at the Climate Systems Analysis Group at the University of Cape Town in South Africa, with funding from the UK Department for International Development, and the article was edited by Anna Taylor.