WaterWorld version 2.87 was applied at 1km spatial resolution for northern Madagascar to determine baseline and the impacts of a land use change projection. Version 2.87 does not include processes of infiltration and subsurface flow.
The baseline simulation provides the following results:
Annual mean water stress (percent of demand not available) indicating significant demand not met in western Madagascar for some months (especially near the coast)
Population with poor quality water (>50.0 HF) annual average (persons) indicating pockets of reduced water quality throughout the areas with small areas of many people potentially affected where populations occur downstream of mining areas
Human footprint on water quality (% contamination) (%) shows agriculture and urban areas to be important sources and mining as point sources with a number of major rivers significantly affected
Annual total water balance (mm/yr) by pixel and by HydroSHEDS basin indicates very high water balances in the East of the country, much lower water balances in the West and negative water balances in the south west (indicating an excess of evapotranspiration over local rainfall and thus a groundwater and river-fed regime)
Percent of water balance contributed by fog inputs (%) indicating around 5-7% deposition over a large part of the country but much higher impaction fluxes to forests in the East
Seasonality index (Walsh and Lawler, 1981) for Water balance (mm/hr) [the higher the index, the higher the seasonality with values >1.0 indicating most water available in 3 months]. The index shows a very high seasonality in water balance the centre and west of the country.
A scenario for land use change was developed using the following rules:
...leading to a change in tree cover between the baseline and scenario as shown here indicating significant deforestation along existing and new transport routes in the north east of the country around the Ankeniheny-Zahamena Corridor (CAZ)
The scenario leads to the following changes in hydrological ecosystem services:
The deforestation leads to increases in water stress in a few places where the reduction in cloud water inputs is greater than the reduction in evapotranspiration and thus water balances decrease but most places show a decrease in water stress as a result of decreased forest evapotranspiration. Changes are more prominent in the drier west of the country.
The human footprint on water quality map indicates that the deforestation and conversion to pasture leads to significant decreases in water quality, especially for the small catchments draining to the east.
The change in annual total water balance shows an increase (because of reduced evapotranspiration) in the lowland forests on the eastern coast and in the west of the island but a decrease (because of a greater reduction in fog inputs than increase in evapotranspiration) in the higher elevation forests in the cloudier zones of the CAZ. This leads to decreases in per capita water availability in the east but increases in the west. In percentage terms these represent between -6% and +10%. Some areas thus show increases in runoff and these cumulate downstream, others (especially in the east) show a decrease in runoff which also cumulates downstream. In the CAZ, decreases dominate.
Small increases in flow seasonality result from the changes in fog inputs and evapotranspiration in some areas and small decreases in flow seasonality occur in other areas