ACCUMULATED TEMPERATURE

A summation of mean daily temperature values above a chosen threshold value, expressed as degree days or heat units. The threshold value is often taken as 6°C, representing the minimum temperature necessary for the commencement of growth in temperate cereal crops and grasses. This is an index of the efficiency, as opposed to the length, of the thermal growing season. Variants of the index are used outside of agricultural applications to quantify heat stress and energy demand. Significant changes in accumulated temperature may accompany more modest changes in mean temperature. As many crops have known bioclimatic requirements, in terms of degree-days for germination or ripening, their responses to future climatic scenarios may be modelled. Similarly, the potential impacts of globalwarming on heating or cooling energy demand may be examined using variants of the degree-day concept.