Water Flow Regulation

The Eastern Arc Mountains are the source of a significant proportion of Tanzania’s water, providing drinking water for all the major coastal cities, irrigation water for most of eastern Tanzania, and the water used to generate 50-70% of the country’s electricity. Despite its importance, however, the regulation of water flow has been the hardest of our focal services to model and map, because robust modeling approaches are extremely data-demanding yet the availability of information on rainfall, water flows and soils – even though better than for most of sub-Saharan Africa - has proved to be limited.

We have compiled all available data on rainfall, river runoff and soil characteristics across the Eastern Arc. These permitted the successful parameterisation of a spatially explicit, daily model of water runoff (called SWAT) for two Arc catchments – the Ruvu and the Sigi basins.

Re-running this model to assess the impacts of land-use change envisaged in our scenarios shows that widespread conversion of natural vegetation to agriculture would increase total runoff especially in the rainy season (as trees evapotranspire more than crops), increase soil losses (and hence sediment loads) through erosion, and decrease dry season flows.

In parallel with this work we have developed a new monthly water balance model, WatR, which is less spatially and temporally detailed but also much less data-hungry and so can be applied across our entire study area. It shows that important areas for water provision include large wetlands (e.g. the Kilombero Valley and the Mkata wetlands) and those Eastern Arc Mountain peaks closest to the Indian Ocean. WAtR also confirms our basin-scale finding that habitat conversion would increase wet season and reduce dry season river flow.

Ongoing hydrological work includes the cross validation of WatR and SWAT and the valuation of water services.

Main Papers:

Fisher, B., Burgess, N.D., Kulindwa, K., Mwanyoka I., and R.K. Turner (2010) Common pool resource management and PES: Lessons and constraints for water PES in Tanzania. Ecological Economics 69, 1253-1261.

Lopa, D., Mwanyoka, I., Jambiya , G., Masoud, T., Harrison, P., Ellis-Jones, M., Blomley, T., Beria, L. van Nordwijk, M. and Burgess, N.D. (2012) Towards operational Payments for Water Ecosystem Services in Tanzania: A case study from the Uluguru Mountains. Oryx 46: 34–44.

Zemadin, Birhanu (2008) Hydrological analysis in the Eastern Arc Mountains. Partly supported PhD thesis. Department of Engineering, University of Dar es Salaam, Tanzania.

Platts, Phillip (2012) Spatial modelling, phytogeography and conservation in the Eastern Arc Mountains of Tanzania and Kenya. Partly supported PhD thesis. University of York, UK.