The city of Quito is located in the foothills of the Pichincha volcano, at an average altitude of 2 800 m. The whole metropolitan area is subject to recurrent serious flooding, landslides and mudslides, causing both obstruction and destruction of the city's drainage and sewerage system and damage to public and private infrastructures. To try to solve this problem, the Empresa Municipal de Alcantarillado y Agua Potable of Quito (EMAAP-Q), together with the Instituto Nacionál de Meteorologia e Hidrologia (INAMHI) and the French Scientific Research Institute for Development through Cooperation (ORSTOM) set up a research project with the following aims : identify the risks caused by extreme hydrometeorological events affecting the slopes of the Pichincha volcano and the metropolitan area of Quito, characterise associated physical and stochastic processes, and provide operational tools for prevention. The present study was carried out within the framework of this programme. Data from over fifty observation sites are used to describe the main spatial and ternporal characteristics of rainfall. The first results presented in this paper will provide the basis for studies that will take into account the rainfall typology and anisotropic nature of the environment in calculating the characteristics of floods of rare frequency.