Mapping of flooding hazards and risks: a semiquantitative approach

Abstract

This paper describes a semi-quantitative approach involving the determination of numerical scores for the mapping of flooding hazards and risks (and related phenomena such as flash flooding and ponding), which was developed and applied in different municipalities of the State of São Paulo (Southeastern Brazil). Hazard assessment and zoning require ways of estimating the probability of flooding phenomena as well as their potential spatial distribution and magnitude. Risk assessment procedures incorporate land use analysis to estimate the vulnerability of different elements (or features), including housing, urban equipment (such as industry, hospitals, etc.), and transportation infrastructure. This leads to the delineation of risk zones and a range of numerical values that indicate the severity of risks of each zone. Estimation of potential damage is meant to qualify the risk in the respective zone, thus expressing possible losses (regarding human lives, materials and economy), in terms of number of dwellings and dwellers, urban equipment and facilities (industry settlements, mining sites, hospitals, etc.), and the extent of roads to be affected by flooding and related phenomena. The application of the method in seven municipalities situated in the Paraíba do Sul River Valley (eastern São Paulo) has allowed the identification and characterization of 85 areas of risk, involving 5,257 dwellings, 34 major urban equipment and facilities (schools, public parks, sport facilities, industrial and mining sites, industry-commercial storage facilities), and approximately 20 km of roads and streets. In São José do Rio Preto (northwestern São Paulo) 11 areas of risk were identified, totaling 104 dwellings, 95 services and commercial facilities, and 5 urban equipments including the main public library, bus and train Stations, plus about 10 km of roads and streets. Tables of data and hazard and risk zoning maps from Guaratinguetá (Paraíba do Sul River Valley) and São José do Rio Preto are presented as examples of the results achieved and the applicability of the proposed approach in distinct geomorphological, hydrodynamic, and socio-economic contexts. Assessment based on numerical scores allows comparative analyses and ranking between hazard and risk zones situated in the same and in different municipalities, which will be useful for the management of existing situations of risk, emergency response and urban planning.