1 CNR-ICTIMA, Padova, Italy 2 Consorzio Padova Ricerche, Padova, Italy Urban Climatology Applied to the Deterioration of the Pisa Leaning Tower, Italy D. Camuffo 1 , G. Sturaro 2 , and A. Valentino 2 With 10 Figures Received December 28, 1998 Revised February 18, 1999 Summary Among the peculiarities of the urban climatology, a relevant one concerns the interactions with monuments, which include stone weathering, deposition and removal of airborne pollutants. In order to know more about the case of the Pisa Leaning Tower, Italy, a field survey has been made for one year, measuring the microclimate interacting with the structure, the vertical temperature and humidity profiles, the Tower surface temperature at different locations and the concentration of particles in air. Also more general information was collected studying the meteorological parameters in the area of Pisa. The correlation between rainfalls and wind evidenced that the windborne droplets arrive from preferential directions, determined on the regional scale by the sea shore on the west (sea breeze) and the channelling operated by the valley of the Arno river on the west. The tilting of the Tower gives a natural shield to the southern part, which is hardly washed by rainfall. The complex balance between airborne particulate matter deposition, tower tilting, rainfall washout and surface runoff determines the pattern of the black crusts which disfigure the elegance of this historical building. The land and sea breezes transport air with different moisture content, and the urban heat island accentuates the mid day drop on relative humidity, determining condensation- evaporation cycles in the stone micropores. The urban climatology of Pisa and the interactions with the Leaning Tower are discussed in view of the conservation of this monument. 1. Introduction The Pisa Tower (Fig. 1), included on UNESCO's World Heritage list, was built between 1173 and 1370 with the foundations partially posed over an underground channel on slightly clayey and sandy ground. The characteristic leaning began around 1278 and lately reached the alarming level of 5  28 0 , corresponding to some 10% (Jamiolkowski, 1995; Veniale, 1995). The risk of structural collapse does not represent the only problem for its conservation. The integrity of the architectonic elements and the safeguard of the stone surfaces, damaged by physical, chemical and biological weathering, are relevant aspect, too. For this reason, research was commissioned to a multidisciplinary group of scientists for a careful planning of a restoration to be carried on together with the structural interventions and the present paper is a part of this research pro- gramme. The aim of this paper is to analyse the interactions between the local climate, the urban environment and this monument. The climate of Pisa (Rapetti and Vittorini, 1978; Pinna, 1958) is in¯uenced by the Medi- terranean, with mild temperature (Fig. 2) ranging in average between 7 and 23  C, but with some departures that in the period 1956±1995 reached 12 and 36  C as extremes. Rainfall (930 mm/ year) is more abundant in autumn (October, 121 mm; November, 116 mm) with a minimum in summer (July, 20 mm). Being a coastal site, the wind rose shows two prevailing directions: the eastern one (which is the direction of the land Theor. Appl. Climatol. 63, 223±231 (1999)