The dataset contains observed and simulated meteorological and hydrological data in western Mongolia. Meteorological data (met_X_obs.csv) contain monthly mean air temperature (T) and precipitation (P) observed at the 28 stations since 1990. Station details and metadata are summarized in "west_mongolia_met_station_metadata.csv". Air temperature and precipitation extracted from the ERA5 reanalysis data are also available (met_X_era5.csv). Hydrological data (hyd_X_xxx.csv) contain monthly mean runoff observed at the 30 stations since 2000. Station details and metadata are summarized in "west_mongolia_hydro_station_metadata.csv". Simulated runoff (dis), glacier meltwater (glc), and runoff with non-glacier configuration (noglc) are also available. Catchment means of annual precipitation (APR) and summer mean temperature (SAT) are available (hyd_XXX_w.csv). MB.csv: Simulated glacier mass balances of 652 glaciers averaged for 2000-2020 are compared with remotely sensed geodetic mass balances by Hugonnet et al. (2021). Detailed descriptions for the simulation are available in Khalzan et al. (2025).