Applicability of cadastral data to support the estimation of water use in private swimming pools

Studies addressing outdoor water use in residential areas rely on surveying methods, the manual digitization of aerial imagery and remote sensing-based approaches to estimate water consumption by different land uses. Publicly available cadastral data potentially offer a more efficient avenue for researchers to obtain information on land use parameters, but few assessments of their quality and applicability have been conducted. A sample of three local areas, encompassing more than 12,000 plots in low-density residential areas and representative of different socioeconomic profiles, were selected in the metropolitan area of Barcelona and along the Mediterranean coast of Catalonia. The reliability and sufficiency of the Spanish cadastre were assessed for the identification of swimming pools against the ground truth evidence provided by high-resolution aerial imagery and the support of object-based image analysis. Omission and commission errors of the cadastre were measured, the delimitation of digitized pool areas was statistically tested for accuracy, and the condition of the facilities was compared in the three study sites. The results do not support the use of the Spanish cadastre as a source of data for uses requiring a high level of detail and completeness. Plot size, socioeconomic and cultural factors affect pool size, the frequency of empty pools and the installation of pool covers in different communities. The study demonstrates that researchers need to complement cadastral data with qualitative information about the condition of the swimming pools to successfully estimate their cumulative water consumption at larger scales. Implications for water use research and spatial planning are discussed.