Recent glacial recession in the Rwenzori Mountains of East Africa due to rising air temperature

Based on field surveys and analyses of optical spaceborne images (LandSat5, LandSat7), we report recent decline in the areal extent of glaciers in the Rwenzori Mountains of East Africa from 2.01 +/- 0.56 km(2) in 1987 to 0.96 +/- 0.34 km(2) in 2003. The spatially uniform loss of glacial cover at lower elevations together with meteorological trends derived from both station and reanalysis data, indicate that increased air temperature is the main driver. Clear trends toward increased air temperatures over the last four decades of similar to 0.5 degrees C per decade exist without significant changes in annual precipitation. Extrapolation of trends in glacial recession since 1906 suggests that glaciers in the Rwenzori Mountains will disappear within the next two decades

Hydrogeochemical processes in groundwater in Uganda: a national-scale analysis

Groundwater represents a vital source of freshwater to meet distributed, rapidly rising demands for safe drinking water, irrigation and industry in low-income countries across the tropics. The hydrochemistry of groundwater within deeply weathered crystalline rock aquifer systems that predominate at low latitudes, is determined primarily by long-term biogeochemical weathering of the parent bedrock. Here, we evaluate geochemical footprints and baseline chemical quality of groundwater that have developed from water-rock interactions across a range of geological environments in Uganda using a national database of hydrochemical and hydrogeological records from 3271 locations. Sampled groundwaters are mostly shallow (69% of samples from depths of <20 m below ground level), fresh at time of drilling (Electrical Conductivity <1000 μS cm−1 in 96% of samples), and of good quality (<8% of samples exceed WHO (2011) guidelines values for chemical parameters in drinking water). Unpalatably high concentrations of total soluble and suspended Fe are, however, common (21%) in meta-igneous, granitic and metamorphic formations. The dominant (95%) anionic facies of groundwater is bicarbonate (HCO3−), indicative of localized flow systems (i.e. discontinuous aquifers) in which chemical evolution of groundwater (e.g. as per Chebotarev sequence) is minimal. Low well yields (82% < 3.6 m3 h−1) and specific capacities (84% < 5 m2 d−1) support this inference; low aquifer transmissivities and storage serve to regulate naturally groundwater withdrawals (i.e. impacts of over-abstraction are localized). Overall, the results attest to the intrinsic high quality of groundwater that occurs in deeply weathered crystalline rock environments in Uganda, which may be expected across tropical Africa

Hydrological and climatological change associated with glacial recession in the Rwenzori Mountains of Uganda

The areal extent of tropical icefields in the Rwenzori Mountains of East Africa has reduced steadily over the last century from 7.5 km^{2} 2 in 1906 to <1 km^{2} in 2003. Considerable debate persists regarding the impact of deglaciation on alpine riverflow and changes in climate driving glacial recession in the East African Highlands. Recent field surveys combined with historical observations reveal continued, rapid retreat in the terminal positions of valley glaciers (Speke, Elena). Observed acceleration in the rate of termini retreat since the 1960s is shown to arise, in part, from the morphologies of the glaciers and the beds within which those glaciers reside. Historical data combined with the first measurements of alpine riverflow in the Rwenzori Mountains show that the contribution of meltwater flows from dwindling icefields to alpine riverflow is negligible, contributing <0.5% of the mean annual river discharge recorded at the base of the mountains. Preliminary high-frequency monitoring of air temperature and humidity in the vicinity of icefields on the Rwenzori Mountains indicates that elevated daily maximum air temperatures coincide with episodic reductions in relative humidity and increased meltwater fluxes observed during the dry season. A sustained reduction in humidity to account for observed deglaciation is not evident from records of lowland precipitation, humidity or river discharge. Lakelevel records in East Africa are also inconsistent with a sudden decrease in regional humidity around 1880AD that is proposed to have triggered deglaciation in the East African Highlands. Water levels in the lakes proximate to the icefields of Mount Kenya and Kilimanjaro are rising in the late 19th century when glaciers on these mountains are observed to be in retreat. Lake levels do not, furthermore, indicate that enhanced humidity over the 19th century prior to 1880AD relative to the 20th century. Evidence of warming over the latter half of the 20th century and an earlier onset of deglaciation (~1870AD) from meteorological and palaeolimnological data suggest that the timing and drivers of deglaciation in the Rwenzori Mountains are consistent with the recession of alpine icefields elsewhere in the tropics

Climate change and the aquatic ecosystems of the Rwenzori Mountains, Uganda

The Rwenzori Mountains are home to one of the last remaining tropical icefields outside of the Andes. Over the last century, equatorial icefields of the East African highlands have been steadily shrinking but the precise climate tropical alpine glaciers remain unclear. More than a decade had passed since the last detailed measurements of glacial cover were made in the Rwenzori Mountains. Recent evidence from Kilimanjaro suggests that its icecap will disappear entirely by the year 2020(1). The Rwenzori glaciers contribute meltwater flows to aquatic ecosystems of the Rwenzori Mountains National Park, a Word Heritage Site featuring spectacular, rare Afroalpine flora and fauna, and are headwaters of the River Nile. With the overall aim of assessing the impact of recent climate change on alpine aquatic ecosystems of the Rwenzori Mountains, a collaborative, international research team led by the University College London (United Kingdom) and Makerere University (Uganda), and involving the Institut für Geographie from the University of Innsbruck (Austria) and Water Resources Management Department (Uganda) was assembled in order to pursue three primary scientific objectives: • to assess the magnitude of current glacial recession; • to assess the impact of glacial recession on alpine riverflow; and • to assess recent environmental change from observational datasets and available, environmental archives stored in lake sediment and glacial ice

Improving the use of climate change information for adaption in Uganda

There is little doubt that climate change is already affecting the lives of people in Uganda. Climate change is a particular challenge for the effective management of the country’s water resources. Reliable information on climate change scenarios and impacts is essential to inform policy and practice. While several climate experiments (e.g. CMIP6) are already available, new experiments such as the 4.5 kilometre-scale convection-permitting regional climate simulations for Africa (CP4A) can now be used alongside the CMIP experiments and allow us to assess the impacts of intense storms in more detail than before. However, if these innovative methods are to influence policy, they first need to be well-understood and accessible. This requires capacity strengthening of the professionals and researchers so that they can analyse such experiments. This workshop provided an opportunity for practitioners in Uganda to learn about a range of climate experiments and see results from case studies focussed on water resources, tea production and urban flooding using the CP4A and CMIP experiments. This was a great opportunity particularly for early career staff at the Ministry of Water and Environment, Ministry of Agriculture Animal and Fisheries and Uganda Electricity Generation Company Limited (UEGCL) as well as researchers at Makerere University

On the application of rainfall projections from a convection-permitting climate model to lumped catchment models

Climate change is predicted to increase rainfall intensity in tropical regions. Convection permitting (CP) climate models have been developed to address deficiencies in conventional climate models that use parameterised convection. However, to date, precipitation projections from CP climate models have not been used in conjunction with hydrological models to explore potential impacts of explicit modelling of convective rainfall on river flows in the tropics. Here we apply the outputs of a continental scale CP climate model as inputs to lumped rainfall-runoff models in Africa for the first time. Applied to five catchments in the Lake Victoria Basin, we show that the CP climate model produces greater river flows than an equivalent model using parameterised convection in both the current and future (c. 2100) climate. However, the location of the catchments near to Lake Victoria results in limited changes in extreme rainfall and river flows relative to changes in mean rainfall and river flows. Application of CP model rainfall data from an area where rainfall extremes change more than the change in mean rainfall to the rainfall-runoff model does not result in significant changes in river flows. Instead, this is shown to be a result of the rainfall-runoff model structure and parameterisation, which we posit is due to large-scale storage in the catchments associated with wetland cover, that buffers the impact of rainfall extremes. Based on an assessment of hydrological attributes (wetland coverage, water table depth, topography, precipitation, evapotranspiration and river flow) using global-scale datasets for the catchments in this research, this buffering may be extensive across humid regions. Application of CP climate model data to lumped catchment models in these areas are unlikely to result in significant increases in extreme river flows relative to increases in mean flows

Characteristics of high-intensity groundwater abstractions from weathered crystalline bedrock aquifers in East Africa

Weathered crystalline bedrock aquifers sustain water supplies across the tropics, including East Africa. Although well yields are commonly <1 L s−1, more intensive abstraction occurs and provides vital urban and agricultural water supplies. The hydrogeological conditions that sustain such high abstraction from crystalline bedrock aquifers remain, however, poorly characterised. Five sites of intensive groundwater abstraction (multiple boreholes yielding several L s−1 or more) were investigated in Uganda and Tanzania. Analysis of aquifer properties data indicates that the sites have transmissivities of 10–1,000 m2 day−1, which is higher than generally observed in deeply weathered crystalline bedrock aquifers. At four of the five sites, weathered bedrock (saprolite) is overlain by younger superficial sediments, which provide additional storage and raise the water table within the underlying aquifer. Residence-time indicators suggest that: (1) abstracted water derives, in part, from modern recharge (within the last 10–60 years); and (2) intensive abstraction is sustained by recharge occurring over several decades. This range of encountered residence times indicates a degree of resilience to contemporary climate variability (e.g. short-term droughts), although the long-term sustainability of intensive abstractions remains uncertain. Evidence from one site in Tanzania (Makutapora) highlights the value of multi-decadal groundwater-level records in establishing the long-term viability of intensive groundwater abstraction, and demonstrates the influence of intra-decadal climate variability in determining the magnitude and frequency of recharge