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.