This paper is based on the fact that some climatic variables show a preferential directionality and grant a markedly anisotropic character to the weathering system acting on rocks. The aim of this work is to quantify the anisotropic degree of the weathering system and its effects on rock erosion. For this purpose, a new methodology based on the vector analysis of directional and time-dependent parameters is proposed to quantify the annual or seasonal anisotropy of the weathering system. Results show that, on the one hand, wind-driven rain and solar radiation are the most anisotropic variables, being north and east the most intense directions for wind-driven rain and southeast for solar radiation, in the case of the San José Tower, the reference monument of this study. On the other hand, the ranking from the most to the least eroded façades of the tower are: east (maximum recession depth of 26.77 mm) > south (15.53 mm) ≈ west (13.56 mm) > north (6.37 mm). Solar radiation and indirect processes arising therefrom are the most important weathering agents in the semiarid Mediterranean climate, whilst wind-driven rain is the main erosion factor especially due to its torrential character. According to our results, weathering and erosion agents are strongly anisotropic, which emphasizes the importance of integrating the anisotropic character of the weathering system in preventive strategies against surface deterioration of monuments. In this sense, this paper advances the United Nations' 2030 Agenda for Sustainable Development.