A previously calibrated MODFLOW-NWT groundwater-flow model (https://doi.org/10.3133/sir20205118) was used to determine the effects of climate variability under a range of future climatic conditions on groundwater resources in the reach 1 of the Washita River alluvial aquifer in western Oklahoma. The study area focuses on reach 1 of the Washita River alluvial aquifer; the entire Washita River alluvial aquifer consists of four administrative sections, or reaches, that are designated as reaches 1–4 by the Oklahoma Water Resources Board (OWRB, 2012). To approximate a range in future base-flow conditions in reach 1 of the Washita River alluvial aquifer and base-flow into Foss Reservoir, the Coupled Model Intercomparison Project Phase 5 Global Climate Model climate data were downscaled to watershed scale using monthly Bias-Correction Spatial Disaggregation techniques. A time series of scaling factors was developed and spatially interpolated for three climate scenarios (central tendency, warmer/drier, and less warm-wetter) representing a range of future climate conditions for the period 2050–2079. These scaling factors were then applied to an existing soil-water-balance model (https://doi.org/10.3133/sir20205118) with climate data for the baseline period 1985–2014 to produce recharge and evapotranspiration estimations for this future period. The downscaled climate data were applied to the groundwater-flow model of the reach 1 of the Washita River alluvial aquifer using MODFLOW-NWT. This data release contains the input and output files for the scenarios described in the associated model documentation report (https://doi.org/10.3133/sir20245082).