Model calculations of incident shortwave radiation were performed for the Mount Kenya massif with the objectives of: (i) exploring the major factors controlling the ice distribution in the peak region: and (ii) determining the primary forcings that led to the differential retreat of the various glaciers.The ice distribution on Mount Kenya, characterized by largest glaciers to the south and east, is primarily controlled by the precipitation pattern. By contrast, the radiation pattern is unconducive to maintaining this ice distribution, as insolation tends to be higher on these largest glaciers. Spatial variability in the incident radiation is mostly due to shading effects, with cloudiness however being more important in reducing absolute values. Steep slopes, essentially above 5,100 m, and higher temperatures below 4,600 m are further limiting factors.A drastic glacier recession is borne out by mappings ofthe ice extent in 1899 and 1963. Over this time span, the number of glaciers diminished from 18 to 11, and another disappeared since 1978. Of the eight defunct ice entities, six were small. By far the largest glacier to disappear since the turn of the century was the Kolbe, in a precipitation-abundant but radiationally very exposed location on the eastern flank of the mountain. The largest and now easternmost ice body, the Lewis, which occupies the radiationally most exposed location of all the glaciers, has experienced the greatest ice wastage.The model calculations indicate that the drastic ice recession since the late 1800s is largely due to an increase in absorbed shortwave radiation accompanying, and in part brought about by, changes in cloudiness, precipitation, and temperature. In addition to the consequences for the overall ice amount, the spatial distribution of radiation totals, as influenced by topographical shading, appears to account for the remarkably diverse shrinkage of the glaciers on Mount Kenya.

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ABSTRACT. The retreat of the glaciers on Mount Kenya is quantitatively well documented for the intervals 1899-1963 and 1963-1987. The ice recession between 1899 and 1963 was strongly dependent on solar radiation geometry. By contrast, the ice thinning between 1963 and 1987 amounted to about 15 m for all glaciers regardless of topographic location. This suggests that climatic forcings other than solar radiation have become more prominent.Sensitivity analyses indicate that the energy supply of about 5 W m-2 , required to produce the observed ice thinning through melting, can be accounted for by a combination of climatic forcings. The direct effect of changing atmospheric composition ("greenhouse effect") on the net longwave radiation could have contributed less than I W m- Long-term station records show little warming trend for East Africa itself. However, mid-tropospheric specific humidity trends of about 0.6gkg-1 over the past two decades in the equatorial belt have been reported in the literature, and considered to be consequences of "global warming" and the "greenhouse effect".Viewed in perspective, the ice wastage on Mount Kenya between 1963 and 1987 appears to have been driven primarily by three climatic forcings, conceivably all steered by the "greenhouse effect": a direct forcing through the net longwave radiation; an indirect forcing through warming and therefore enhanced sensible heat transfer; and another indirect forcing through warming (not necessarily in the region itself), leading to increased (advected) atmospheric moisture, and hence to reduced latent heat transfer, this last line of control being the most important.

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Measurements at various epochs in the course of the twentieth century indicate a slowing down of surface ice flow velocity. This is consistent with the numerical modeling of the secular glacier recession, which furthermore shows a gradual upward shift of the regions of highest velocity and mass flux. Crevasse orientation is transverse above, and longitudinal below, the velocity maximum. The secular change in the longitudinal velocity profile seems to affect the crevasse pattern. Net balance in the next five years is a major factor in future changes of the glacier. With this reservation, model calculations for a possible extreme scenario indicate a drastic overall velocity decrease, and a moderate further displacement of the velocity and mass-flux maxima up-glacier, by the mid 1980’s.