Uncertainty of drought information in a data-scarce tropical river basin

•Evapotranspiration deficit index-based drought is susceptible to data uncertainty.•Evapotranspiration data used were from a hydrological model and remote sensing.•Results show scenario uncertainty in drought duration, severity, and intensity.•Localized severe drought intensity was due to low rainfall and model uncertainty.•Model-based and remote sensing-based overall drought intensity were moderate. The Wami River basin in east-central Tanzania features the Eastern Arc Mountains and dichotomous climate regimes. Drought characteristics are vital in planning and managing water resources in river basins. However, the estimation of drought characteristics from the evapotranspiration deficit index (ETDI) is susceptible to the uncertainty associated with alternative datasets from hydrological models and remote sensing images. Thus, this study investigated scenario uncertainty in ETDI-based drought characteristics in the river basin using evapotranspiration and potential evapotranspiration data from a classical Soil and Water Assessment Tool (SWAT) and the Moderate Resolution Imaging Spectroradiometer (MODIS) images between the years 2000 and 2010. The findings showed a substantial scenario uncertainty in drought duration, severity, and intensity at various locations in the river basin. Localized severe MODIS-based overall drought intensity (MODIS-ODI) in the middle of the basin was attributed to prolonged low rainfall amounts. In the downstream, localized severe SWAT-based overall drought intensity (SWAT-ODI) was attributed to an imperfection of the SWAT model in simulating the true hydrologic cycle of the river basin. However, at the basin level, both SWAT-ODI and MODIS-ODI between the years 2000 and 2010 were moderate. These findings can be used as the baseline information in improving drought estimation in the river basin. Moreover, this study also demonstrates the importance of assessing scenario uncertainty in drought characterization.