Ifanadiana Topographic Wetness Index (TWI)

The Topographic Wetness Index (TWI) estimates the tendency of water to pool based on a pixel’s slope and location within a hydrological catchment. These values were estimated for the four major villages and aggregated to the fokontany level.

Columns :
- comm_fkt : name of fokontany using standardized ‘new_commune’_’fokontany’ nomenclature
- mean_twi : Average TWI value in a 1km buffer surrounding the four major villages in a fokontany. Calculated using a building-weighted mean.

Data and Resources

Additional Info

Field Value
Author Michelle Evans
Maintainer RANDRIANJATOVO Tokiniaina
Last Updated August 20, 2025, 14:22 (UTC)
Created July 16, 2025, 15:40 (UTC)
Data link Created as part of Evans et al. 2025 (doi: 10.1186/s12936-025-05266-0). Can be accessed via the associated figshare repository.
Processing steps The TWI is calculated based on the SRTM Digital Elevation model using the GRASS GIS function ‘topidx. It estimates TWI as ln(a/tan(β)), where a is the surface catchment area of that pixel and β is the local surface topographic slope. These values were then extracted using a spatial mean (weighted by included pixel area) around two zones of interest: within a 1-km radius of major villages and in rice paddy areas. These values were aggregated to the level of the fokontany via a building-weighted mean