Land use and climate change effects on water yield from East African forested water towers

Abstract. East African forested mountain regions are vital in generating and

supplying water resources to adjacent arid and semi-arid lowlands. However,

these ecosystems are under pressure from both climate and land use changes.

This study aimed to analyze the effects of climate and land use changes on

water yield using the Budyko framework as a first-order conceptual framework assuming steady-state for pristine/protected forested areas. For nine

selected forested water towers in East Africa, the amount and distribution

of water resources and their decadal changes were analyzed. Results show

that most areas inside and outside the water towers are under pressure from

human influences. Water yield was more sensitive to climate changes compared

to land use changes within the selected East African water towers

themselves. However, for the surrounding lowlands, the effects of land use

changes had greater impacts on water yield. We conclude that the

East African water towers have seen a strong shift towards wetter

conditions, especially in the period of 2011–2019, while, at the same time,

the potential evapotranspiration is gradually increasing. Given that most of

the water towers were identified as non-resilient to these changes, future

water yield is likely to also experience more extreme variations.