What is a GCM (General Circulation Model)?
In short: A General Circulation Model (GCM) is a numerical model that simulates the large-scale climate system on a three-dimensional grid. It represents interactions among the atmosphere, ocean, land surface, and cryosphere using physical equations and parameterizations. GCM output is essential for climate projections, but its grid scale is usually too coarse to represent a weather station directly.
What a GCM produces
GCM archives contain variables such as temperature, precipitation, pressure, humidity, wind, and radiation for historical experiments and future forcing scenarios. Different models respond differently, so impact studies often examine an ensemble rather than treating one model as exact.
Why downscaling is used
A GCM grid-cell value is an area-scale simulation, not a point measurement. Downscaling and bias correction translate that large-scale information into data whose spatial scale and historical statistics are more useful for local applications.
SD-GCM converts coarse CMIP5 and CMIP6 GCM output into bias-corrected local climate series.