Climate-glacier relationship on Mount Kenya

A combined investigation of glacier history and multi-scale climate dynamics on tropical high mountains - from both field measurements and modelling - has the potential for revealing a sophisticated history of climate in the tropical mid-troposphere, where routine meteorological measurements are very rare. Complementary to our glacier-climate studies on Kilimanjaro we propose to perform a glacier-climate study on Lewis Glacier, Mount Kenya. For Lewis Glacier, the most comprehensive tropical glacier data set is available and respective analyses promise to provide detailed information about post Little Ice Age glacier-climate interactions in a multi spatio-temporal scale. Whereas Kilimanjaro provides insight to atmospheric moisture related glacier and climate variations and changes, from Mount Kenya - that is 1000 m lower - we expect also information on air temperature variations and trends. Conceptually, measured detailed short term and long term annual glacier mass balances - the first to be measured in field experiments, the latter available for 1979 to 1996 - provide the basis for optimising and evaluating a glacier mass balance model. By modelling mass balances from gridded atmospheric information an improved state of understanding in terms of enhanced time, space and process resolution can be achieved. In a next step, these improved mass balance series will be statistically related to large scale climate patterns and modes. For selected events and for classes of mass balance conditions meso-scale atmospheric dynamics on the mountain will be studied with a regional climate model. With the proposed project we expect to provide comprehensive insight to processes and multi-scale drivers that cause the growth and decay of glaciers on Mount Kenya. Finally, we plan to merge findings from Kilimanjaro and from Mount Kenya toward a new state of understanding on climate over tropical East Africa, particularly in the mid troposphere.

The aim of this research was to find out what the changes in the volume of Lewis Glacier on Mt Kenya through time can tell us about the climate conditions of the past. Lewis Glacier has been shrinking for more than hundred years, but we need to understand how prevailing climate conditions determine the amount of loss in any given year.We calculated the volume changes of the glacier since the first available map in 1934 until 2010 and found that although the glacier is considerably thicker than previous estimates, only 10% of the glacier volume from 1934 remained in 2010. By 2014 observations showed that the glacier is beginning to split into two parts. Over the whole surface of Lewis Glacier melting occurs almost every day, and these conditions are similar to the lowest parts of glaciers in the tropical Andes, further confirming that the current climatic conditions cannot sustain Lewis Glacier.The annual amount of snowfall is the primary factor controlling the glacier mass balance (which is negative for mass loss) through adding mass and reflecting solar radiation due to its brightness. However, even in periods of considerable snowfall on the glacier, if this coincides with daily average temperatures which are frequently above 0C, then melting is sufficiently vigorous to remove both the snowfall and, subsequently, underlying glacier ice. Therefore, snowfall amount alone is not a complete indicator of whether the glacier will be gaining or losing mass, and the seasonality of rainy and dry periods does not translate into seasons of mass gain and mass loss for the glacier as might be expected. Therefore, it is difficult to attribute former changes in glacier size to changes in a single climatic characteristic or season.Nevertheless, comparison of the available annual glacier mass balances long?term climate reanalysis data (which is produced by interpolating measured climatic variables using a physical atmospheric model) show that on annual timescales the mass balance of Lewis Glacier is less negative when the local atmosphere at the elevation of the mountain summit is moister and cloudier. The annual mass balance also shows some relation to the El Niño Southern Oscillation (a periodic seesaw of sea surface temperature patterns in the tropical Pacific with global impacts mainly on air temperatures), which appears to be primarily expressed through its influence on air temperature and its impact on glacier melt rates during the first 5 months of the year.