Historically, several catchments were planted with pine to determine the impact of afforestation on streamflow. Results were definitive and influenced policy and the Water Act.

Scientists (IPPC) and economists (World Economic Forum) agree that climate change, with the expected increases in extremes, poses a significant threat to lives and livelihoods. In our water-scarce South Africa, these impacts on water security are (should be) of paramount concern. Water availability helps drive economic prosperity. Lack thereof not only cripples economic growth but imperils human well-being and livelihoods.  Accepting the reality of the “generic impacts” of climate change, such as “expect more extreme droughts and floods”, is not always sufficient to inform specific responses at local scales, nor provide sufficient evidence to influence policy to mitigate risks.

Likewise, simply tracking changes in water resources is not in itself useful. For knowledge to be sufficiently beneficial to society, it needs to illuminate the processes and dynamics behind observed changes in water resources. If these are understood, effective leverage points for land management actions and policy interventions can be identified for mitigation and adaptation.

Integrated research approach

Resolving relative impacts of climate, land-use and land-cover change, as well as the interlinking processes between these, requires an integrated research approach. An advantage of the Cathedral Peak research catchments, situated within one of South Africa’s most important strategic water source areas, is the relatively pristine nature of several of the research catchments. This provides the opportunity to detect and attribute specific climate change-related signature impacts, without being confounded by human-induced land-use impacts on water quality and quantity.

When the Grasslands Node started in 2011, four of the “pristine” fire climax mesic grassland catchments were prioritised for refurbishment. We adopted an integrated approach to investigate how the energy balance, natural biodiversity template, carbon dynamics and meteorological processes, among other things, are interacting and how changes in climate may be affecting these dynamics, leading to a net impact on water quantity and quality.

However, early engagement with our stakeholders in the development of the platform resulted in the consensus to harness the opportunity of including additional research catchments representing alternative management scenarios. These included a “degraded” catchment which had previously been afforested with exotic pine trees, as well as a catchment where fire is intentionally, albeit not always successfully, excluded. These carbon-rich mesic grasslands are designed to burn!

By including the previously afforested catchment (considered degraded) as well as the fire exclusion catchment typified by woody encroachment, a burgeoning number of studies involving multiple institutions are taking advantage of the comparative value of these different land management scenarios. Consequently, knowledge being generated is starting to reveal how land management scenarios alter processes relative to the “pristine benchmark” and associated water resources emanating from this vital water source area.

For example, SAEON is measuring the evapotranspiration (ET) over the three land management scenarios – near pristine grassland, degraded (typified by bracken fern vegetation) and fire exclusion (typified by woody encroachment). We are using the surface renewal methodology in the degraded and woody encroached catchments, and the eddy covariance techniques in the grassland. We have looked at the comparability of these methods, and published a paper showing that the cheaper surface renewal method is comparable to the expensive eddy covariance method for ET measurements in the mesic climate of Cathedral Peak.

Seasonal pattern

A seasonal pattern in the ET is evident for all three land covers. During the summer months the ET over the three land covers is comparable, except in the drier years when the ET from the grassland is lower than that from the bracken and woody species. For example, during the summer of 2019/2020 the ET over the grassland was lower than the bracken and woody species ET. Transitioning from summer to winter, the bracken and woody species continue to transpire at a higher rate than the grassland for longer, and they maintain a higher ET throughout winter. The woody species transpire the most during the core winter months.

These differences translate ultimately to different impacts on streamflow. The more transpiration, the less water available for streamflow. A direct policy implication related to this is that intact grasslands should be protected, and woody encroachment and afforestation in mesic grasslands should be avoided at all costs.

In conjunction to this, carbon studies by PhD candidate Lindo Dlamini are revealing the impact of these different land management scenarios on carbon dynamics. These in turn also impact on hydrological processes because of how carbon influences infiltration and storage of water. Results are indicating how important and more effective grasslands are as carbon stores.

These are just some examples of how SAEON’s long-term observations from the Cathedral Peak long-term research platform, building on influential historic research, are starting to bear fruit. The return on continued investment to run the platform will keep increasing with time, enabling us to address critical issues for society.