Accurate water resources assessment using hydrologic models can be a challenge anywhere, but particularly for developing countries with limited financial and technical resources. Developing countries could most benefit from the water resource planning capabilities that hydrologic models can provide, but these countries are least likely to have the data needed to run these models. Model-based hydrologic assessments are a necessity in developing countries due to limited national and international funding for water improvement projects. WaSSI (Water Supply Stress Index) is a relatively simple hydrologic model requiring a limited number of data inputs. Despite the simplicity, WaSSI predictions of streamflow at the watershed scale have been shown to correlate well with measured data at the monthly and annual time step. Therefore, WaSSI is a good candidate for use in hydrologic modeling in developing countries. As a case study, this paper presents an example of hydrologic model development, testing, validation, and projection using WaSSI for the developing country of Rwanda. Rwanda has a mixed landcover with approximately 20% of the nation covered in forest that range from dense mountain forests, to lower elevation open forests types. Leaf Area Index (LAI) is a primary driver of evapotranspiration (ET) within WaSSI. Therefore, as forest LAI increases with density, predicted ET increases and streamflow decreases. We found that the data for validation of model streamflow from long term monitoring stations was limited due to measurement error. However, the WaSSI model showed promise when modeled streamflows were compared to the limited measured data using globally available model input parameters. Although we suggest that global model input data is sufficient for long-term water resource planning, we strongly encourage the development of increased hydrologic monitoring capacities in developing countries as part of international water conservation and development efforts.
McNulty, S.; Cohen, E.; Sun,G.; Caldwell, P. 2016. Hydrologic modeling for water resource assessment in a developing country: the Rwanda case study. In: Lachassagne, P. and M. Lafforgue (eds). Forest and the Water Cycle: Quantity, Quality, Management. Cambridge Scholars Publishing. pp 181-203