Add ReWaterGAP (#1110)

Author: ekatef

README.md

@@ -1653,6 +1653,7 @@ parameter values.
 - [Niche Vlaanderen](https://github.com/inbo/niche_vlaanderen) - A hydro-ecological model that predicts the potential occurrence of (ground)water-dependent vegetation types in an area based on information about the (abiotic) site conditions.
 - [Amanzi](https://github.com/amanzi/amanzi) - Provides a flexible and extensible parallel flow and reactive transport simulation capability for environmental applications.
 - [fluvgeo](https://github.com/FluvialGeomorph/fluvgeo) - An R Package for Performing Fluvial Geomrphology Analysis.
+- [ReWaterGAP](https://github.com/HydrologyFrankfurt/ReWaterGAP) - A global-scale hydrological simulation software for quantifying water flows and storages on all continents of the Earth.
 
 ### Ocean Models
 - [MOM6](https://github.com/NOAA-GFDL/MOM6) - A numerical representation of the ocean fluid with applications from the process scale to the planetary circulation scale.