Evaluating and modelling the impact of extreme events on South African dryland rivers: Cyclone Dando (January 2012)

In mid January 2012, Cyclone Dando struck southern Africa, leading to widespread heavy rainfall (450-500 mm in 48 hours) & flooding in the Kruger National Park (KNP), eastern South Africa. This flooding occurred just 12 years after the last major catastrophic flooding in the KNP (Jan/Feb 2000), which also caused dramatic river channel & vegetation changes. Using data acquired from light aircraft (photographs, LiDAR) together with field surveying & sediment sampling, this study will exploit a rare opportunity to investigate the flooding, erosion & sedimentation that occurred during the January 2012 event along three rivers in the KNP. The data obtained will be compared with pre-existing data that were collected prior to & following the 2000 flooding in the KNP, & then combined with state-of-the-art computer models to simulate flow characteristics during floods & the longer term response of the rivers to sequences of extreme floods. The aerial, field & modelling results will help to develop new conceptual models of the response of these rivers to extreme events. Such models will have practical application, both for river managers in the KNP & farther afield. Many climate change scenarios predict future increases in the size & frequency of extreme flood events in southern Africa & other dryland regions, & better understanding of the spatial extent of flooding, erosion & sedimentation will contribute to improved flood hazard management & environmental stewardship.

The main beneficiary of the findings arising from the Urgency Grant objectives (O1-O3), & from the follow-up objectives (O4-O9) that are based on this urgent data collection phase, will be South African National Parks (SANParks). SANParks are responsible for the management & conservation of biodiversity within South Africa's National Parks, including the Kruger National Park (KNP) (see Appendix 1). The KNP is a reserve of international conservation significance & one of South Africa's premier tourist attractions. Conservation practice in the park tends to focus on the management of flora & fauna but landforms provide the dynamic template upon which the ecological system is based. Along the KNP rivers, for instance, flood disturbance helps to create a mosaic of habitats of different substrate type, age & hydroperiod, thus promoting biodiversity. River management in the park, however, tends to focus on the short-term (sub-decadal) issues of sedimentation & vegetation colonisation that tend to reduce flood conveyance capacity & habitat diversity in the intervals between extreme floods, & the beneficial aspects of extreme flood disturbance events in longer term development of the river corridors are not yet widely appreciated, neither by the park authorities nor the general public.

The rare opportunity provided by Cyclone Dando to evaluate the decadal-scale response of KNP rivers to successive extreme flood events in 2000 & 2012 will thus contribute to a belated but growing recognition of the importance of physical processes such as flooding, erosion & sedimentation as a driver of habitat diversity. Negative aspects of extreme flood events include damage to tourist camps & other park infrastructure, but improved understanding of the controls on the spatial extent of flooding, erosion & sedimentation may provide information that can be employed in re-siting or re-alignment of camps, roads & bridges. While these recent extreme flood events cannot by themselves be taken as an indication of the effects of global warming, they may provide clues as to what may happen more frequently in future. Many climate models are predicting future increases in weather extremes in southern Africa & other dryland regions, so the findings may also contribute to more robust projections of dryland channel & riparian vegetation change under conditions where flood magnitude & frequency will be altered. This will help to place shorter term management concerns in appropriate spatial & temporal context, enabling scarce money & resources to be targeted more effectively & preventing inappropriate management responses to extreme floods & extended droughts.

Underpinning the proposal is a more generic research approach. This approach integrates aerial & ground-based data collection with numerical modelling techniques to develop new numerical & conceptual models that will generate insights into the interactions between atmospheric, earth surface & biospheric processes. Adoption & translation of this kind of research approach into UK-specific contexts by the research team or other research or consultancy groups will contribute to improved flood hazard management & environmental stewardship, & also provide tangible environmental, social & economic benefits. Key beneficiaries of this kind of generic research approach will be the Environment Agency & other statutory bodies responsible for managing flood levels, erosion & sedimentation in environmentally-sensitive floodplain, wetland, estuarine & coastal areas.