Droughts are a common occurrence in water-scarce areas. Climate change caused by humans has contributed to climate change.. Rainfall reduction is the main driver. However, temperature and evaporation can also play an important role.
The catchment area, where rain falls and flows into rivers, is another factor that can influence drought severity. These factors include the type and amount of vegetation in the catchment area and the soil characteristics.
Catchment restoration can be used to offset the impacts of climate changes on water resources. It can include revegetation, wetland rehabilitation, gully rehabilitation, alien tree clearing, and wetland restoration. This is just one type of restoration. Nature-based solutionsThese organizations focus on reducing climate change impacts by working with nature.
But it’s not easy to tell what difference restoration makes on the impacts of Climate change is being caused by humansWater availability during droughts
In a Recently published analysisWe examined the impact of climate change on catchment conditions in the 2015-2017 period. Cape Town “Day Zero” drought. This drought resulted in one of the most severe water crises that any city has ever faced in recent years. The drought was caused by a prolonged shortage in rainfall, which led to river flows that gradually depleted the reservoir storage in the area.
We wanted to see whether clearing alien trees from mountain catchments where the city’s water comes from would have lessened the impacts of climate change on the drought. This is the first study to examine the potential of nature-based solutions for protecting society from extreme events directly related to climate change.
We found that clearing alien trees before the drought hit could have reduced the impact of climate change on water supply during the “Day Zero” drought. However, it couldn’t have prevented all of the human-driven impacts on water availability from climate change.
Water supply and alien trees
South Africa invasive alien tree clearingIt is a well-known type of catchment restoration. These trees have spread to many mountain catchments that are vital for water supply. Alien trees You should drink significantly more waterBecause they are taller and have more leaf area, and have deeper root systems, they are better than native vegetation. These characteristics increase transpiration and leave less water for groundwater recharge and river flow. Aliens trees have a negative impact on water, especially during droughts when water is most important.
This is not an isolated South African problem. All over the world, studiesYou can see a decrease in water yields after afforestation (planting of trees).
Human influence on the precipitation shortages and decreased river flows
Between 2015 and 2017, a very rare drought event — The worst since 1904 — pushed Cape Town into a Water crisis. Researchers have previously shown that climate change is responsible for the decrease in rainfall that led to the crisis. ThreeTo Six times more likely.
These studies were focused on the problem of rainfall shortage. But Cape Town’s water is dependent on river flows from distant mountainous catchments. These catchments provide water. Six large dams were used to capture and store the data.. During the drought, dams levels dropped to They are able to use less than 20% of their potential.
Our AnalyseThis study was done to determine whether removing alien trees from mountain catchments would have reduced the effects of climate change’s lower rainfall on river flows.
We created simulations of worlds using climate models and hydrological models. We also used hydrological models to simulate worlds without and with human-driven climate change. This was done for two mountain catchments that are typical of those that supply the water. Western Cape Water Supply System which feeds Cape Town’s water delivery.
Our results show that climate change has reduced river flows during droughts by 12-29% in comparison to a world without human influence on the climate. This was greater than the 7-15% drop in rainfall from these catchments, which we could attribute to climate changes. As water moved from rain to rivers, the climate change effect was amplified in the catchments.
Similar to Previous workWe found some influence of climate change on evaporation, but not very large.
Our analysis showed that clearing out alien trees before the drought hit could have helped to reduce the impact of climate changes on river flow during drought. Clearing catchments with moderately infested alien trees (40% coverage) could have helped to reduce river flow reductions caused by climate change by 3-16%. The spread of alien trees that fully cover catchments could have prevented 10-27% more streamflow reductions due to climate change.
Our analysis reveals that clearing all catchments completely would not have fully offset the climate change impacts.
While catchment restoration is a good option for managing drought risk, it does not address climate change’s impact on water resources. It is important to combine catchment restoration with other adaptation options in water-scarce zones that are facing a warmer, drier world.
In many cases, however, climate change isn’t the only cause of water scarcity. Poor management, poor services, and inadequate infrastructure can easily override all the benefits that nature-based solutions may offer.
Our results suggest that while nature-based solutions may be beneficial, it is important to remember that they should be context-specific. It is crucial to understand the local conditions before designing any response. DM
Petra Holden – Researcher, University of Cape Town; Alanna Rebelo – Senior Researcher, Agricultural Research Council; Joyce Kimutai –
Climate Scientist, University of Cape Town; Kamoru Abiodun Lawal – Postdoctoral Research Fellow in Atmospheric Science, University of Cape Town; Mark New – Director, African Climate and Development Initiative, University of Cape Town; Piotr Wolski – Senior Researcher in Hydro-Climatology, University of Cape Town; Romaric C Odoulami – Postdoctoral Research Fellow, University of Cape Town; and Tiro Nkemelang – PhD student at the University of Cape Town in African Climate Risk.
First published by The Conversation.