Large-ensemble 21st century monthly hydro-climatological forcing dataset for the reference (REF) scenario. The REF scenario implements no explicit climate mitigation policy (no specific greenhouse gas emissions target) anywhere in the world for the sake of abating climate change, except for some energy policies such as fuel economy standards, renewable electricity requirements, the gradual phase-out of old coal power plants, reduced use of exhaustible resources, and conventional pollutants reduction. The REF scenario represents the upper bound of climate change risks. The dataset consists of a 900-member ensemble, which is constructed by spatially disaggregating a 50-member ensemble of the MIT IGSM zonal climate projections based on hydroclimate change patterns from the 18 CMIP6 climate models. The dataset contains nine key meteorological variables on a monthly scale from 2021 to 2100 at a spatial resolution of 0.5°x 0.5°, including precipitation, air temperature (mean, minimum and maximum), near-surface wind speed, shortwave and longwave radiation, specific humidity, and relative humidity. The abbreviations of the variables are listed as below: precipitation (Prep), air temperature (mean (Tair), minimum (Tmin) and maximum (Tmax)), near-surface wind speed (WIND), shortwave (FSDS) and longwave (FLDS) radiation, specific humidity (Huss), and relative humidity (Hurs).