??Researchers used isotope hydrology techniques to develop a pioneering method to assess how different sources of water sources contribute to river flow dynamis.
Dr Andrew Watson, a post-doctoral fellow in the School for Climate Studies at Stellenbosch 肆客足球, collaborated with researchers from the International Atomic Energy Agency (IAEA) to advance this new method. The result, published in Nature Water recently, is an important breakthrough in the understanding and prediction of deep water drainage (aquifer recharge) and flooding risk.
For this study, the researchers analysed data from 136 perennial rivers and 45 large catchments globally, including the Orange and Tugela rivers in South Africa and the Congo river in west-central Africa. They used measures of the stable isotopes of oxygen and hydrogen making up water molecules to characterise the fraction of river flow that is due to “young water" (i.e., water derived from recent rainfall events), compared to “old water" (ranging from a few months to hundreds and even thousands of years).
The study was also able to characterise river flow dynamics through developing a dynamic water retention indicator. In rivers with high dynamic retention, water moves through the catchment slowly, indicating a slower response to hydroclimate events. The study further attributed these indicators to key factors such as land cover (e.g. crop and forest cover) and climate (such as air temperature and precipitation).
In the case of the African rivers, all three had low dynamic water retention capability, implying that they will be more susceptible to hydrological extremes like droughts and floods, Dr Watson explains.
Revealing the secrets of river flow
Rivers flow long after rain has fallen and can flow far from the origin of the rain and snow that supplies rivers with water. This is because rain and melted snow can follow a complex path through a catchment, over the surface, or via storage in the soil or even deeper in aquifers. Water is also evaporated or transpired by plant roots.
The fractions of all these varies from river to river and these fractions can be used to predict how a river will respond to changing conditions.
“With climate and land-use change now significantly altering how water moves through river catchments, this approach offers a new tool for risk assessment and water planning purposes," commented Prof Guy. Midgley, interim director of the School for Climate Studies and not involved with the study.
“This will be valuable in climate change adaptation across the world and has direct relevance in South Africa and the southern African region," he added.
Image above: The Orange river at Vioolsdrif in South Africa. Credit: RudiBosbouer, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
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