Goedverwacht: what do the scientists models tell us? 23 May 2013

Key findings * impact of land use (irrigation farming) and alien vegetation in the catchment will have a bigger effect on water in the river than climate change * no significant change in rainfall (which means that changes in rainfall due to climate change won't be noticeable given the existing rainfall variability) * there are potentially more significant impacts on rainfall and runoff in surrounding areas due to climate change including more frequent extreme events such as floods or droughts (also possibly in Goedverwacht) * the number of hot days will increase significantly and the number of cold days will decrease significantly due to climate change

How accurate are these findings? (the science behind the results) * The scientists use mathematical models to project the climate in the future * They have to make decisions about which models to use and what information to put into the models * First: they choose a storyline which helps determine how much greenhouse gas will be in the atmosphere due to human activity * For this study, they picked the IPCC’s A2 scenario (this assumes the world is similar to how it is now…with not much international cooperation and with economic & technical development confined to certain regions)

How accurate are these findings? (the science behind the results) * Second: decide how many models to use * They used10 out of the possible 21 that the IPCC recognises for the A2 scenario * Third: define an area (100km 2 ) around Goedverwacht to model

How accurate are these findings? (the science behind the results) * Fourth: use local data from weather stations to inform the models * Limitation: there is only one rain gauge in the defined area * More gauges would give better information for the area and would make errors less likely

No. Raindays/yr No. Days/yr with Rain > 20 mm No. Days/yr with Rain > 35 mm No. Days/yr with Tmax > 35C No. Days/yr with Tmax > 40C No. Days/yr with Tmin < 5C Historical ( ) Change Intermediate - Present CC CN CS E E G G Gi IP MR Avg change Projected changes

Projected changes in daily temperature In the 1990s, approximately 23 days a year were hotter than 35C By mid-century, approximately 38 days a year will be hotter than 35C In the 1990s, approximately 21 days a year went below 5C By mid-century, only approximately 5 days a year will go below 5C

In Goedverwacht we need to respond to… More hot days Fewer cold days Possibly more droughts and floods in Goedverwacht region Land use changes and alien vegetation Neighbouring farmers responding to climate change (e.g. impact on water, jobs, food) Low carbon economy (less use of fossil fuels such as petrol, diesel, coal for electricity, etc.)