QGIS
The free, open-source GIS that has become the default spatial platform for water engineers worldwide.
250m, 16-day global vegetation index composites — the standard input to crop-coefficient ET and drought indices.
by NASA / LP DAAC
MOD13Q1 delivers atmospherically-corrected NDVI and EVI vegetation index composites at 250m resolution every 16 days, globally, from 2000 to present, distributed through LP DAAC. EVI improves on classic NDVI in high-biomass and atmospherically-hazy conditions, which matters for tropical and heavily-vegetated catchments.
Vegetation index time series feed crop-coefficient-based ET estimation, vegetation-drought indices (VCI, VHI) and land-cover classification training data — a quiet workhorse behind a lot of remote-sensing-based water balance work.
Other geospatial & hydro-gis tools covering similar workflow stages.
The free, open-source GIS that has become the default spatial platform for water engineers worldwide.

500+ fast geospatial analysis tools with the best DEM hydrology toolkit in open source.
JAXA's 30m global DSM from PRISM stereo imagery — a strong third opinion alongside SRTM and Copernicus DEM.
A 30m global DEM reaching to 83° latitude — the go-to where SRTM/NASADEM have no coverage at all.
Esri's free hydrology framework for ArcGIS Pro — terrain preprocessing and the data model behind many agency workflows.
ESA's TanDEM-X-derived global DEM — the most accurate free global surface model available today.