Kenya's Tana River - the longest in the country - snakes through a river basin which encompasses a huge range of ecosystems, from lush forests along the upper reaches of the river on the slopes of Mount Kenya to dry rangelands and even coastal mangroves where the river meets the Indian Ocean.
This area in the south of the country is home to a vast array of plants and animals. Some species are found nowhere else in the world, like the endangered Tana River Red Colobus monkey. It also encompasses some world-renowned protected areas that are popular with tourists.
In our paper we modelled climate change-related risks to the terrestrial biodiversity (birds, mammals, reptiles, amphibians and plants) of the Tana River Basin. Large reductions in species richness - compared with preindustrial levels - are projected with just 2C warming. Birds and plants will likely feel the greatest impact.
We identified potential spaces within the basin where many species could survive in a warmer world - known as refugia. But many overlapped with areas already converted to agriculture or set aside for agricultural expansion. Most are outside protected areas.
Similarly, some protected areas contain no projected refugia at higher levels of global warming, showing they may be insufficient to protect the basin's biodiversity as climate changes.
Our modelling found that risks to biodiversity are much smaller if the Paris Agreement's goal of limiting global warming to "well below 2C" warming, rather than 2C only, is met.
Our research provides the first assessment of the combined effects of development plans and climate change on the biodiversity of the Tana River Basin, including identifying potential areas for restoration. It contributes to a greater understanding of biodiversity protection and adaptation options in Kenya.
What we found
We found that at least 23% of Kenya's Tana River Basin could act as refugia if temperatures remain within the goals of the Paris Agreement, which aims to keep global warming well below 2C. Our models showed that limiting warming would be particularly beneficial to plants. This would have a knock-on effect for animals as they will depend on the plants for food and shelter.
But our modelling showed that the potential for refugia for plants and animals decreases strongly with warming. For example, 82% of the basin is estimated to act as a refugium for the plants currently present at 1.5C warming, as compared with 23% at 2C and 3% at 4.5C.
Unfortunately, under Kenya's National Spatial Plan, agricultural expansion is planned for many of these important refugia, particularly those in the north of the basin around the mountains.
To avoid a trade-off between biodiversity protection and development, careful planning is needed.
And expansion of protected areas should be on the cards.
The current network of protected areas, which cover around 16% of Kenya's land area, will not be enough to conserve the iconic species of southern Kenya. Further areas should be set aside or restored for wildlife.
Based on the location of refugia, our study also identified places that could be restored. Some are within spaces already designated for biodiversity protection, such as the Tana River Primate Reserve, which has been severely degraded in recent years.
Given the global commitment to restoring degraded ecosystems, it is also important to understand how the plant species used in this restoration will fare in the face of climate change.
With higher warming levels, we found that not only are the majority of refugia lost but also the potential for restoration becomes more limited as native species become unable to survive the higher temperatures and changing rainfall patterns.
It is vital to keep up the restoration initiatives, such as tree planting, that are already under way, while also being mindful of the fact that climate change could prevent those new trees from growing. Those planting must think about climate change when deciding on the most suitable trees. It is important to get the right species in the right place and ensure they can tolerate warmer temperatures and support native biodiversity.
The challenges of climate change and biodiversity protection must both be taken into account within Kenya's development activities. It's already evident that species are moving to new places due to climate change. Infrastructure development in Kenya must take this movement into account.
Global action is also needed. These challenges associated with the climate and biodiversity crises will only be solved with urgent action to reduce greenhouse gas emissions globally.
The ultimate goal of the Paris Agreement is to pursue efforts to limit warming to 1.5C. The world has already warmed 1.2C since preindustrial times, so we are running out of time to meet this target. Strong commitments from global leaders ahead of this year's climate change summit in Glasgow are urgently needed. Responses must consider the climate and biodiversity crises simultaneously. Failing to do this could lead to the extinction of wildlife not just in the Tana River Basin, but across the globe.
Maintaining spaces for biodiversity alongside development will be really beneficial, as these ecosystems can provide a range of benefits to humans. For instance, maintaining natural areas close to agricultural areas can help support crop pollination by providing suitable nesting and foraging habitats for pollinators.
Author: Rhosanna Jenkins - University of East Anglia