Growing Season Length Map

MetriClima assigns hourly ERA5-Land 2 m air temperature to longitude-derived local solar calendar days and calculates their arithmetic means. A local day is valid when at least 22 finite hourly values are available; an invalid or entirely missing local day breaks a qualifying run.

Following the core ETCCDI/climdex definition, the growing season starts on the first day of the first run of at least six consecutive valid days with mean temperature strictly above 5 °C, searched only in the first half of the agricultural year. It ends on the first day of the first run of at least six consecutive valid days strictly below 5 °C, searched from July 1 in the Northern Hemisphere and January 1 in the Southern Hemisphere. If a valid onset occurs but no qualifying termination is found, the growing season extends to the end of the agricultural year.

Northern and equatorial agricultural years run January–December; southern agricultural years run July–June and are labeled by their starting year. An agricultural year is valid with at least 350 valid local days and at least 170 valid days in each half. Start and end dates are normalized to a 365-day agricultural calendar before duration is calculated. A valid year with no qualifying onset contributes zero days, while an invalid year is excluded; the map is the arithmetic mean of valid annual durations across 2011–2025.

Longer values indicate a longer thermally defined growing season under the 5 °C rule. They do not guarantee adequate heat for ripening, sufficient moisture, or freedom from frost. Freezing temperatures can still occur within this thermally defined season.

In very warm climates the season may approach the full year. In cold climates, a valid agricultural year with no qualifying onset contributes a zero-day season.