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Naivasha Virtual Fieldcourse

Climate change

Symptoms of climate change are evident in large portions of the Lake basin. As reported by local farmers, highland temperatures are increasingly mild; this allows growing beans at higher altitudes than 2 decades ago, but at the same time it increases the spreading of agricultural pests. The occasional appearance of ice has disappeared from the mountain tops (Mau and Aberdare forests) and even the permanent glacier present on Mount Kenya itself (5,199 m a.s.l.) has virtually entirely vanished. While the majority of scientists as well as official Kenyan and International authorities belive that impacts such aws these should be ascribed to changes in the composition of the atmosphere, in particular the rise in the concentration of CO2, monitoring conducted in the Lake Naviasha Basin underlines the connection between changes in temperature and deforestation. A recent concept, known as the Biotic Pump mechanism, provides a background theory by means of which deforestation, temperature changes and drought can be connected.

As illustrated in the diagram here above, the original situation (left panel) was characterised by a cool dense primary forest which used to favour the internal recycling of nutrients (N=nitrogen, P=phosphorus) and the slow release of water towards the lower basin. The effect of this slow release of water, retained within the forest biomass and its deep soils, used to generate moderate water level changes. Under this scenario agricultural pests are relatively few and slowly growing. A possible worsening future is portrayed in the right panel. Under this scenario the forest is cut to expose the bare soil, generating massive erosion. The sun shines more frequently and intensely, and the temperature rises promoting faster development of agricultural pests and greater proportion of infested crops. Instead of being recycled, nutrients become released towards the lake generating eutrophication, algal blooms, and poor quality conditions for coarse fish predators (birds as well as predatory fish). The fast release of water that is not anymore retained by tree roots and by organic forest soils, produces wide water level fluctuations in the lake.

In the video clip here below, Jan Pokorny' explains how deforestation and rise in temperature can diminish the capacity of the landscape to promote cloud condensation and precipitation. The Biotic Pump theory is the only one that supports the common knowledge, shared by farmers within the Lake Naivasha Basin, that forests are able to attract rain.