Recent glacial recession and its impact on alpine riverflow in the Rwenzori Mountains of Uganda

The limited number and duration of hydrological measurements in the East African Highlands inhibit current understanding of the impact of glacial recession on alpine riverflow. From historical records and surveys conducted in the dry season of 2005 and wet season of 2007, we report (1) recent changes in the terminal positions of large valley glaciers (Speke, Elena) and (2) spot measurements of alpine riverflow along altitudinal transects of the principal river (River Mubuku) draining alpine icefields in order to assess the relative contribution of icefields and underlying ecotones to river discharge. Observed acceleration in the rates of termini retreat of the Speke and Elena glaciers since the late 1960s is attributed, in part, to the convex–concave slope profile in which these valley glaciers reside. We show that current glacial recession has a negligible impact on alpine riverflow. Spot measurements of meltwater discharges indicate that icefields contribute considerably less than 2% of the river discharge at the base of the Rwenzori Mountains during both dry and wet seasons. An anomalously high specific discharge of the River Mubuku (1730 mm a−1) arises from high rates of precipitation exceeding 2000 mm a−1 below alpine icefields within Heath-moss and Montane forest ecotones that occupy more than half of the river’s gauged catchment area. For other tropical alpine icefields representing a tiny fraction (<1%) of alpine river catchment areas (e.g. Irian Jaya, Kilimanjaro, Mount Kenya), glacial meltwater discharges are similarly expected to contribute a negligible proportion of alpine riverflow.