Assessing the impacts of climate change variability on water resources in Uganda: Developing an integrated approach at the sub-regional scale (START Project No. 202 457)
Collection of springwater in Bwaise, Kampala, Uganda (photo: Liz Ziegler, July 2003).
- Project summary
This one-year project sought to enhance indigenous scientific capacity to undertake integrated assessment of the sub-regional impact of climate change and climate variability on water resources in Uganda. Through a programme of training and collaborative research, a PC-based regional climate model (RCM), PRECIS (UK Meteorological Office) was implemented. Driven with lateral boundary conditions from General Circulation Model (GCM) simulations of future climate (seasonal forecasts or climate change scenarios), the RCM provides an effective tool to downscale for climate impact assessment. RCM outputs were used to drive soil-moisture balance models of the terrestrial water balance for water resource management applications. The project provided an opportunity for focused dialogue in Uganda between those engaged in the management of water resources (e.g., hydrogeologists, hydrologists) and those engaged in the study and assessment of climate variability and change (e.g., climatologists, meteorologists). The project served to strengthen links between science and policy in Uganda. The project was led by Dr. Charles Basalirwa (Makerere University) with technical support from Dr. Richard Taylor and Dr. Martin Todd (University College London). The project is funded under the START programme (project ref. 202 457 5859) which is co-sponsored by the International Geosphere-Biosphere Programme (IGBP), the World Climate Research Programme (WCRP), and the International Human Dimensions Programme on global environmental change (IHDP).
- Study rationale & objectives
The populations of East Africa are particularly vulnerable to climate change and climate variability, including extreme climatic events such as drought and flooding, due, in part, to reliance upon localised (untreated) water supplies and rainfall-fed agriculture. Predominantly rural populations in Uganda primarily depend upon groundwater for a source of potable water on account of its improved distribution and microbiological quality relative to surface waters. Current efforts to supply safe water to rapidly expanding towns and cities also commonly target groundwater as it necessarily avoids high treatment costs associated with surface-water sources (Taylor and Howard, 2000). This demand for groundwater is expected to increase significantly in the next few decades as the UN (2002) estimates that the current population of 25.8 million is expected to more than double by the year 2025. Despite rapid population growth and dependence upon localised water resources and groundwater in particular, the impacts of climate change on water resources in tropical Africa have been subject of relatively few studies (Hulme et al., 2001) and remain poorly resolved. Moreover, the assessment of the impact of climate change and climate variability on water resources is in its infancy in Uganda. There is a need for enhanced capacity to develop integrated assessment of water resources and the response to climate events.
The climate of East Africa is particularly interesting due to the combination of (i) its relationship to the Indian Ocean circulation system (including the Indian Ocean Zonal Mode and ENSO teleconnections, providing the basis for seasonal forecasting, e.g. Mutai and Ward, 1998) (ii) complex topography (associated with the African rift and the Ethiopian highlands to the north), (iii) the existence of large lakes in the region, and (iv) marked climatic gradients. Predictions of climate change (and natural variability) are (largely) dependent on General Circulation Models (GCMs). Predictions from GCMs of climate change in East Africa through the 21st century tend to suggest: 1) an increase (»10-20%) in rainfall; 2) a change in the seasonal distribution of rainfall with an increase from December to February and a decrease from June to August; 3) an increase in air temperature of 0.3°C to 0.5°C per decade (IPCC, 2001). There is, however, a great deal of uncertainty in GCM predictions. Notably, the resolution of climate information provided by GCMs is too coarse (typically about 300kmx300km) to enable assessment of the regional impacts of climate change. This problem is particularly pronounced in regions such as East Africa with a complex regional climate. Regional climate models (RCMs) with a higher grid resolution (typically tens of km) provide more detailed and more realistic simulations of current climate and predictions of climate variability and climate change for particular areas of interest. The finer spatial scale of RCMs also allows greater ability to detect and predict high frequency variations including extreme climatic events. RCMs are the state-of-the-art tool with which to downscale the coarse scale GCM predictions for climate impact assessment.
Indigenous capacity to evaluate climate variability and predict future climate change in Uganda is currently limited. A PC-based RCM, PRECIS (Providing Regional Climates for Impacts Studies) has been developed by the Hadley Centre (UK) specifically to address the need for countries to make regional-scale climate predictions. In Uganda, a dense and extensive network of meteorological stations exists to assess rainfall variability and, along with recently released high resolution satellite rainfall estimates (Todd et al., 2001), can be used to evaluate output from a locally based RCM at appropriate scales. Output from the PRECIS RCM can also be tested against that from other RCMs already implemented over East Africa such as the NCSU-RegCM2-POM coupled model (Song et al., 2004).
Water resource assessment and management requires climate-driven hydrological models. In Uganda it is vital that such models incorporate of groundwater recharge. Indeed, the role of groundwater in the terrestrial water balance, often ignored, may be significant particularly during drought or low-flow periods (Taylor and Tindimugaya, 1996). Soil-moisture balance models (SMBMs) that simulate changes in soil moisture and groundwater flux and are thus highly relevant to rainfall-fed agriculture (e.g., crop models), have been successfully employed in Uganda to estimate the terrestrial water balance (Howard and Karundu, 1992; Taylor and Howard, 1996; 1999; Tindimugaya, 2000). This work indicates that such models perform well only at high temporal resolution (daily). SMBMs possess a major advantage over other, commonly employed hydrological models that assume static basin storage (e.g., Pitman) in that they provide estimates of groundwater recharge. Input variables to SMBMs (precipitation, soil and vegetation types, pan evaporation data, and air temperature) are widely available in East Africa and can be obtained also from RCMs. Model outputs of recharge and runoff can be constrained respectively by water-level fluctuations and baseflow separation of streamflow discharges (Taylor and Howard, 1999). The Water Resources Management Department of Uganda possesses extensive networks of river gauging stations and groundwater monitoring sites. The latter, instituted throughout Uganda in 1998 with records for some stations since 1994 (Taylor and Howard, 1999), is the most extensive in East Africa.
- to develop the capacity for integrated assessment of climate change and variability on water resources
- to implement a PC-based regional climate model (PRECIS) and initiate evaluation of model output using land-based observations and satellite data
- to develop soil-moisture balance models of the terrestrial water balance
- to develop the capacity to assess the impacts of climate change and climate variability on the terrestrial water balance by integrating soil-moisture balance models and output from the regional climate model
- to provide training in each of these modelling tools and consolidate dialogue between relevant agencies
- Project team
The project links active researchers (Makerere University, University College London) and practitioners (Meteorology and Water Resources Management Departments) with compatible interests in order to promote long-term, inter-disciplinary and international collaboration. Collaboration between Ugandan project team and the wider climate modelling community in Africa (Kamga-ACMAD) will serve to promote further international collaboration and, hence, Ugandan participation in the study of climate change and its impacts in Africa.
- Dr Richard Taylor (Hydrological/Hydrogeological Advisor)
- Dr Martin Todd (Climatological Advisor - now at University of Sussex)
- Dr Charles Basalirwa (PI, Climatologist/Meteorologist)
- Dr Andrew Muwanga (geochemist)
- Abushen Majugu (Meteorologist/Climatologist)
- Callist Tindimugaya (Hydrogeologist)
- Joel Okonga (Hydrologist)
- Dr. Andre Kamga (Climatologist)
- Cited references
- Camberlin, P., S. Janicot, and I. Poccard, 2001. Int. J. Climatol., 21, 973-1005.
- Falkenmark M., Lundqvist, J. and Widstrand, C., 1989. Nat. Res. Forum, 258-267.
- Howard and Karundu, 1992. J. Hydrol., 139, 183-196.
- Hulme, M., R.M. Doherty, T. Ngara, M.G. New, and D. Lister, 2001. Clim. Res., 17, 145-168.
- IPCC, 2001. Climate Change 2001: Impacts, Adaptation, and Vulnerability. CUP.
- Mutai, C.C., and M.N., Ward, 1998. Proc. 23rd Annual Climate Diagnostics Workshop, Miami, Florida, Oct 26-30.
- Song,Y., Semazzi, F.H.,M., Xie, L. and Ogallo, L., 2004. Int. J. Climatol., 24, 57-75.
- Taylor and Tindimugaya, 1996. In: Proceedings of the IVth Nile 2002 Conference, Kampala (Uganda), Vol. A, pp. 87 to 94.
- Taylor and Howard, 1996. J. Hydrol., 180, 31-53.
- Taylor and Howard, 1999. J. Hydrol., 218, 44-71.
- Taylor and Howard, 2000. Hydrogeol. J., 8, 279-294.
- Tindumgaya, 2000. M.Sc. Dissertation (IHE Delft, The Netherlands)
- Todd, M.C, Kidd, C.K., Kniveton, D.R. and Bellerby, T.J., 2001. J. Atmos. Oceanic Tech., 18, 742-755
- UN, 2002. World Population 2002. Rep. ST/ESA/SER.A/224.