This repository contains observational (actual and counterfactual), experimental (actual and counterfactual), and model-based precipitation (pr), minimum and maximum temperature (Tmin, Tmax), reference evapotranspiration (ETo), and self-calibrating Palmer Drought Severity Index (scPDSI)  for each macro-scale watershed in the western US. 

Model-based monthly pr, Tmin, Tmax, windspeed, SH, and downward shortwave radiation were retrieved from 130 ensemble members across 23 GCMs participating in CMIP6. Monthly ETo calculated following the ASCE Penman-Monteith approach, from which scPDSI was derived. 

Observational pr, Tmin, Tmax, windspeed, actual vapor pressure, and downward shortwave radiation were retrieved from Williams et al. (2020), extended through 2023. SH was derived, then monthly ETo and scPDSI calculated (as in above). Counterfactual observational data were created by subtracting the GCM multi-model mean trends in pr, average temperature, windspeed, SH, and radiation from the observational fields. 

These data (model-based and observational) were extracted to five 2-digit hydrologic unit code (HUC2) watersheds–the Upper Colorado Basin (HUC 14), the Lower Colorado Basin (HUC 15), the Great Basin (HUC 16), the Pacific Northwest Basin (HUC 17), and the California Basin (HUC 18)–and spatial means taken. 

The experimental dataset was created using the observational data. Each month was initialized with scPDSI = -4, from which independent scPDSI calculations were run for the subsequent 24 months using the spatial mean of the observed and counterfactual ETo and precipitation data for each basin. 

Description of the data and file structure

This dataset contains a csv file for each of the five watersheds (HUCs 14-18), for each variable (pr, tmin and tmax or tas, ETo, and scPDSI), for observational (actual and counterfactual) and model-based data. Additionally, it contains a csv file of scPDSI values for each of the five watersheds for the experimental data (actual and counterfactual). File nomenclature is as follows: 

Model output:

• HUCXX_var_cmip6.csv (e.g. HUC14_eto_cmip6.csv contains the spatially averaged ETo values for each ensemble member for HUC 14).

Observational: 

• HUCXX_var.csv (e.g. HUC14_ETo.csv contains the spatially averaged ETo values from the observational data for HUC14.) 
• HUCXX_var_EnsembleMean.csv (e.g. HUC14_ETo_EnsembleMean.csv contains the spatially averaged counterfactual ETo values for HUC14.) 

Experimental:

• huc_XX_experiment.csv (e.g. huc_14_experimental.csv contains the experimental scPDSI values for HUC14.) 
• Note, actual data (rows 1-1476) are followed by counterfactual data (rows 1477-1968).