Global 0.25° daily observed and counterfactual fire weather index (1979–2024)

This is the associated dataset and code for the paper "Increasing Synchronicity of Global Extreme Fire Weather." To identify synchronous fire weather, we calculate daily Fire Weather Index (FWI) at 0.25° resolution for the period 1979–2024 using fifth-generation European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis (ERA5) data, based on daily maximum air temperature, daily minimum relative humidity, daily mean wind speed, and daily total precipitation. We also apply an overwintering procedure in our calculations that accounts for inter-seasonal drought in cold climates. To assess the contribution of anthropogenic climate change, we apply the same methodology to derive counterfactual FWI that removes the first-order influence of modeled climate change in the variables used to calculate FWI. The counterfactual is constructed by subtracting the low-pass filtered signal of monthly changes in temperature, humidity, wind speed, and precipitation relative to a quasi-preindustrial climate (1850–1900) as simulated by the multi-model mean of 20 models participating in the Coupled Model Intercomparison Project Phase 6 (CMIP6) from the observational record.