Effect of Climate Change on the Ecohydrology of the Mt. Marsabit Cloud Forest (Northern Kenya)

Mt Marsabit, an extinct volcano located in northern Kenya, has at its summit a sub-humid evergreen cloud forest surrounded by dry forests, shrub lands and desert. This forest is sustained by rainfall (800--1400 mm per year), and a large, but difficult to quantify, amount of moisture captured from low level clouds by the forest canopy (Muchura et al 2014). Mt Marsabit is ecologically and economically important and is the main source of water for its surroundings. Cloud base height is likely to increase in response to global warming but the effects on precipitation and forest area have until now not been quantified. Using satellite vegetation data, we estimate that for 1982--2015 annual precipitation from low level clouds is around 200-1500 mm, similar in magnitude to rainfall. On the south-eastern side and summit of Mt Marsabit variations in vegetation are most closely linked to variations in cloud base height. From 1976-2015 rainfall did not change but cloud base height increased in response to increased air temperature. This increase is in part consistent with a small decrease in vegetation on the south-east side of Mt Marsabit (2000-2015); the north-west side, which has higher correlations with rainfall, showed a small increase in vegetation for 2000--2015. We estimate that the area of dense vegetation cover was over ten times larger during cooler conditions of the Last Glacial Maximum (4 °C lower temperatures) and will decrease by 20 % to 75% in response to a 2 °C warming associated with climate change.