How the assessment works

GCAT compares two things: the climate at a place, now and under future scenarios, and the range of climates a plant has actually been recorded growing in. If the place falls inside that range, the plant is in familiar territory. The further outside it falls, the more the plant is being asked to do something it has not been observed doing.

Each score runs from -9 to 9. Zero means the place sits in the middle of the plant's known natural range. Negative scores mean the place is at the colder or wetter end of that range, or beyond it; positive scores mean the warmer or drier end.

Score values and what each means
Score	What it means
-9	Below known and typical range
-8	Below known range but within typical range
-7	Below known range but parent taxa within known range
-6	Below known range but well within typical range
-5	Below known range but parent taxa well within known range
-4	Below known or typical natural range but within cultivated range
-3	Near the lower limit of known cultivated range
-2	Near the lower limit of known natural range
-1	Near the middle of known cultivated range
0	Near the middle of known natural range
1	Near the middle of known cultivated range
2	Near the upper limit of known cultivated range
3	Near the upper limit of known cultivated range
4	Above known or typical natural range but within cultivated range
5	Above known range but parent taxa well within known range
6	Above known range but well within typical taxa
7	Above known range but parent taxa within known range
8	Above known range but within typical range
9	Above known and typical range

Mean annual temperature (°C): Average temperature across the whole year — the broadest measure of warmth.
Minimum temperature of the coldest month (°C): How cold winters get, which sets the hardiness limit for many plants.
Mean annual precipitation (mm/yr): Total rainfall over a year.
Climate water deficit (mm/yr): How much more water plants could use than the climate supplies — drought stress.
Climate moisture index: Ratio of water supply to demand, so wetness and dryness on one scale.
Vapour pressure deficit (kPa): How strongly the air pulls moisture from leaves — drying wind and evaporative stress.

Historic (1850 estimate): Conditions before industrialisation and urban heat.
Baseline (1970–2000 average): The reference period most climate products are built on.
Current (2025 estimate): Today’s climate, including urban heat.
Low emissions (SSP1-2.6) by 2050: Emissions cut quickly.
Moderate emissions (SSP2-4.5) by 2070: Emissions stay near today’s levels, then fall.
High emissions (SSP3-7.0) by 2090: Emissions keep rising.

Scores describe climate only. Soil, drainage, aspect, shade, pests and how a plant is looked after all matter and are not part of the assessment.
A plant with few records will be scored from little evidence. The record count is shown alongside each result for that reason.
Where a plant has no records of its own, the service may assess a parent or accepted name instead. When that happens it is stated in the results.
Future scenarios are projections, not predictions. Comparing several is more informative than trusting one.

Back to the assessment

How the assessment works

Reading a score

Climate measures

Climate scenarios

What this cannot tell you