To better understand the relationship between energy consumption, and prevailing climatic condition, the present study uses Hong Kong's observed air temperature records, end-use electricity consumption, and population datasets to: (a) investigate the spatial pattern of cooling energy requirement i.e. cooling degree days on a typical normal and extremely hot summer day using co-kriging geospatial mapping technique; (b) analyze the annual trend of cooling degree days in the city; and (c) quantify the impact of extreme heat events on the summer cooling energy requirements. Results revealed reasonable predictability of city-wide cooling degree days with the co-kriging method which uses two covariates i.e. "elevation of the weather station" and "building volume density within the 1000 m radius neighboring area". Homogeneity and heterogeneity in cooling degree days' distribution were found during the summer daytime and nighttime, respectively indicating the method's ability to delineate the urban heat island effect with increased magnitude during extreme heat events. Quantitatively, the extreme heat events increased cooling degree days by 80-140% depending on the event type, a range consistent in recent years (2011-2015). Lastly, we provided the implications of our findings to building and urban design; and future energy planning. (C) 2019 Elsevier Ltd. All rights reserved.