The Rwenzori Mountains of equatorial East Africa are widely known to be the legendary “Mountains of the Moon” described by Ptolemy in 150 A.D. as ‘the Mountains of Moon whose snows feed the lakes, sources of the Nile’. Indeed, snow and ice on these glaciated mountains that straddle the border between the Democratic Republic of Congo (DRC) and Uganda supply water to lakes that are a source of the White Nile as it flows north from Uganda into the Sudan. The mountains are also a hotspot of biodiversity featuring rare Afro-alpine fauna and flora.
Glaciers on the Rwenzori Mountains have receded rapidly over the last century. The estimated extent of icefields determined by field surveys and remote sensing, has declined from 6.5 km2 in 1906 to 1.0 km2 in 2003. If present trends continue, glaciers are expected to disappear from the Rwenzori Mountains entirely within the next two decades.
A definitive explanation of the causes of deglaciation in the Rwenzori Mountains is hindered by the absence of sustained meteorological observations around the icefields. There is, however, evidence of both rising air temperatures and reduced cloud cover as potential drivers of glacial recession; these influences are related as warmer air requires more water vapour to form clouds. At present, icefields occupy a narrow elevation range between 4800 m above mean sea level (mamsl) – the elevation of the 0°C isotherm – and the mountains’ highest summit at 5109 mamsl. The icefields are consequently highly sensitive to current and projected warming.
The Rwenzori Mountains are very wet with year-round rainfall in excess of 3 metres recorded in forest ecosystems below the glaciated summit. As meltwaters from dwindling icefields provide only a tiny contribution (<0.5%) to alpine rivers, river flow is much more strongly influenced by variability in precipitation than deglaciation. Observed warming in the Rwenzori Mountains serves, however, to intensify precipitation resulting in fewer but heavier rainfalls. This transition has been observed globally but is especially pronounced in the tropics.
As similarly reported in a GlacierHub post by Tsechu Dolma from the Himalayas, communities around the Rwenzori Mountains in Uganda and the DRC have experienced an increased frequency and intensity of flood events that have destroyed homes, crops, and transport links. In particular, the footbridges which connect communities are sometimes damaged or destroyed, making it difficult for children to attend schools, and farmers to travel to their fields or to markets. Longer droughts associated with the intensification of precipitation have also impaired crop production around the base of the mountains and increased demand for irrigation. Since projected warming as a result of climate change will amplify the risks of floods and droughts, the development of adaptive strategies to mitigate these impacts is critical.
This guest post was written by Richard Taylor a professor at University College London’s Department of Geography. If you’d like to write a guest post for GlacierHub, contact us at email@example.com or @glacierhub on Twitter.