In the GDD model for Celsius, what base temperature is subtracted from monthly average temperature?

• A. 0°C
• B. 10°C
• C. 5°C
• D. 15°C

Answer: (B)

In this GDD approach, growth is tied to heat above a threshold called the base temperature—the temperature below which development is negligible. For the Celsius version commonly used in practice questions, that base is 10°C. Subtracting this base from the monthly average temperature gives the heat accumulation for that month (or zero if the average is at or below the base). This reflects that many temperate crops start developing only once temperatures exceed about 10°C. For example, a monthly average of 12°C yields 2 degree-days, while an average of 7°C yields zero. The other options would set thresholds that don’t align with this standard convention.