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The role of land-use change on influencing mountain climate on Kilimanjaro, East Africa

Status: completed
Publication State: published


This project investigated the influence of land-use on surface climate (temperature and moisture availability) on Mount Kilimanjaro in Africa. It was funded by the Natural Environment Research Council (NERC) with the grant reference - NE/J013366/1 - lead by Dr Nicholas Pepin (University of Portsmouth).

There has been extensive deforestation on Kilimanjaro and the summit ice-fields are retreating. The water supply on the lower slopes of the mountain are becoming more unreliable with more flash flooding and more periods of drought. The main cause of the summit ice retreat is that the climate is becoming drier, with less precipitation (hence accumulation of snow), and fewer clouds meaning more sunlight which causes intense sublimation and hence ablation. The reasons for drying, however, are not yet well understood. They are believed to be a combination of free air changes due to changes in the Indian ocean upstream to the east, and local-scale land use change (such as deforestation) which may dry out the air locally.

Because the mountain is in the tropics, the sun is strong and it heats the mountain each day. This causes upslope winds that help transport moisture from the rainforests on the lower slopes to the summit region where it is deposited as snow (or at the very least forms cloud that protects the ice fields from sunlight). The upper air itself is normally extremely dry, so it is possible that deforestation could in theory cause ice field decline.

Unfortunately, although we have much high publicity research focusing on the ice-field decline, there is no field data on the slopes of the mountain that measures climate, although high profile and well-funded international campaigns have looked at the mountain summit in isolation. There are also lots of computer models of Kilimanjaro's climate and the effects of deforestation but they have no data against which to validate their simulations.

This project aimed to fill this gap by collecting field observations of temperature and moisture on both the windward dry north-east slope and the lee forested south-west slope, expanding on data already collected by the research team since 2004. The funding allowed collection of three years of data on the south-west slope (11 years in total), and three years on the drier north-eastern slope. As well as the comparison between slopes, data was collected from subsidiary studies at a more local scale (at given elevations on both the south-west and north-east slopes) examining the contrast between vegetated and unvegetated locations.

The results were compared with free-air temperatures and moisture at the same elevations (from reanalysis products and weather balloon records) which showed how the mountain surface itself is influencing the climate. The project also compared the two slopes to quantify the large scale effect of vegetation (the south-west slope has healthy forest cover but the north-east slope does not) and local scale effects by comparing vegetated/non-vegetated readings on both slopes.

The obtained differences could be used to reconstruct mountain climate back in the past, and also to compare/validate the computer models that are attempting to simulate the effects of land-use change on the mountain.

The key objective of this research was to investigate the influence of land-use on surface climate (temperature and moisture availability) on Mount Kilimanjaro in Africa.

The overall aim was to quantify the current climate on Kilimanjaro and thus investigate the potential role land surface changes (including deforestation) may play in influencing glacial change.

The main objectives were:
1. To obtain reliable field observations of air temperature, vapour pressure, and relative humidity (hence cloud cover) on both the densely forested south-west lee slope and drier windward north-east slope of the mountain, covering all elevations of the mountain from 800 m to 5800 m.

2. To supplement the larger scale slope contrast with detailed study of the influence of vegetation at given elevations on both slopes through contrasting vegetated/non-vegetated observations.

3. To compare the surface observations on both slopes with free atmospheric measurements at equivalent elevations, to determine the influence of the mountain surface on generating its own climate. The role of vegetation in controlling these differences will be examined. This will subsequently allow downscaling of surface mountain climate from free-air parameters, and enable reconstruction of surface mountain climate back to 1950 through hindcasting.

4. To use the surface observations to improve model simulations of mountain climate through helping validate modelling efforts which are attempting to assess the influence of land-use change on Kilimanjaro's mountain climate and summit ice-fields.

Abbreviation: Not defined
Keywords: temperature, relative humidity, Kilimanjaro, mountain


Keywords: temperature, relative humidity, Kilimanjaro, mountain
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