The aim of the study was to conduct observations of the surface energy balance in a large (population 3 million) Mediterranean sea port with an old central core and relate the results to features of the climate and surface morphology where the necessary infrastructure was available. One reason for this investigation was that studies of energy partitioning in or near central quarters of old European cities have been scarce. In contrast, most studies have focused on the energy balance of suburban environments particularly in North American cities. Measurements were conducted on the roof of an old massive stone building (the University administration offices) located on the north western edge of the old city and distant 1.7 km approximately from the coastline. Land-uses around the site are mainly museums, church, educational and commercial. The mean height of the 4 to 6 story buildings around the site is about 18 m. Vegetation cover is limited to lines of trees on the wide streets characteristic of the Ensanche development to the W, N and NE. To the E lies the old city with narrow streets and almost no green areas. The site is some 2 km to the west of the observed location of the UCL heat island, almost cloudless skies prevailed during the measurement period.

Results show that as expected the convective sensible heat flux (QH) dominates (34%) over the heat used for evaporation (9%) in view of the scarcity of green areas an the largest proportion going for storage in the building fabric (56%). This energy partitioning is very similar to the one observed in central Mexico City where building fabric is also massive and green areas are scarce. Advection of moist air from the sea seems to play a small role in the value of QE.

Keywords: urban energy balance, heat island, Spain