Why do Cal-Adapt tools default to certain time periods?

Cal-Adapt tools typically display statistics for thirty-year periods. Thirty years is the traditional length of record used in climatological studies and is known as a climatological normal. Thirty years is considered the minimum number of years needed to characterize a regional climate and apply statistical tests. This aligns with best practice in climate science since climate is the long-term trend in prevailing weather conditions. Looking at a climate projection for any one year, or even a few years, is likely to be misleading for adaptation planning because variability is inherent to climate systems and longer-term trends cannot be determined based on a single year’s data. The thirty-year periods in Cal-Adapt capture typical adaptation planning horizons and align with those used in California’s Fourth Climate Change Assessment.

Historical Baseline (1961–1990): The historical baseline is chosen to represent the period in which the majority of California’s critical infrastructure was developed. This thirty-year period represents the period in which anthropogenic climate change signals were beginning to be felt.

Mid-Century (2035–2064): The mid-century period is a thirty-year period centered on 2050, the middle of the century.

End of Century (2070–2099): The late-century period is the last thirty years of the 21st century for which all model runs are available.