VARIATIONS IN HEATING AND COOLING DEGREE-DAYS IN THE SOUTH-EASTERN USA, 1960-1989

Temporal trends and spatial variability of heating and cooling degree- days are examined for a portion of the south-eastern USA for the perio d 1960-1989. Temporal variability is examined through simple time-seri es analyses, regression analyses, and a climate departure index (CDI). Maps of 30-, 15-, 10-, and 5-year climatic normals for degree-days ar e presented. The CDI indicates that heating degree-day (HDD) variabili ty was high during the 1970s with a sudden drop to low variability dur ing the 1980s. Simple regressions show weak downward trends for actual HDD values across the region during the study period. However, the HD D decline was more pronounced through the 1980s, coinciding with the p eriod of low year-to-year variability. Isoline maps show that most sit es recorded distinctly fewer HDD in the most recent 5-year period comp ared with longer term averages. Although the long-term trend for cooli ng degree-days (CDD) is slightly positive, there is considerable inter yearly and interdecadal variability. Unlike HDD, there were no sustain ed periods with consistently high or low variability for CDD. Mapped p atterns of climatic normals show that CDD values peaked across the stu dy area during the most recent 5-year period. Mapped patterns for both HDD acid CDD can be influenced by data for large urban sites. Repeati ng the analyses without the seven largest urban centres resulted in le ss anomalous spatial patterns but almost no shift in study area mean-d egree-day or CDI values and their temporal patterns. Atlanta emerged a s the most distinct anomaly for the mapped patterns. From an applied v iewpoint, the most significant finding occurred for the heating season with the combination of a sustained downward trend in HDD and compara tively low variability around the long mean (Low CDI values) during th e last 13 years of the study period. This period represents a span whe re the climate-driven demand for space heating was decreasing and the heating-season generating capacities for power generation utilities we re not challenged.