ABSTRACT
The transboundary basins of Minho and Lima Rivers are shared between Spain and Portugal and are integrated into an International River Basin District (RBD). In the Spanish River Basin Management Plan, a combined drought index (CDI), based on precipitation and runoff indices, is currently applied for drought monitoring. In this study, we assess the performance of this CDI over the two Portuguese sub-basins. We compare a) the CDI with other drought indices, and b) in-situ measurements of hydrometeorological variables with estimates from TerraClimate dataset, as alternative data source. The results suggest that the Standardized Precipitation and Evapotranspiration Index can be an alternative to the CDI, as it is highly correlated and detects very similar drought periods, while requiring less input data and calculation effort. The TerraClimate products prove to be a suitable complementary data source. It is suggested that a vegetation drought index should be incorporated into an improved CDI.
