Urbanisation and climate change effects on urban drainage performance : a case study of SUDS in a risk area in the city of La Paz, Bolivia

Abstract

The city of La Paz in Bolivia has witnessed many disaster events attributed to a surplus of rainfall, causing flooding and landslides on urban settlements. This study presents a quantitative evaluation of the effects of urbanisation and changes in rainfall-induced climate change in the drainage system of a selected area in District Sur of the city. Initially, the urban sprawl was determined by analysing the land-use changes between 2000 and 2020, using GIS tools over Landsat 7 imagery. A collection of historical disaster events and projected rainfall patterns, based on scientific research, allowed constructing rainfall scenarios from existing storm data. A study area was selected based on the land-cover transformation, disaster occurrence and risk zones. These factors served as input data for the Storm and Water Management Model (SWMM) developed by the Environmental Protection Agency (EPA) of the United States. Two scenarios were considered in the digital model and simulation. The first scenario analysed peak flow, flooding, and overloaded elements under land-use changes, based on the urbanisation sprawl of 2003, 2013 and 2020. The second scenario added a design storm with climate factors of reduction/increment of rainfall due to climate change. Also, this scenario considered only the current conditions of land use as of those in 2020. In scenario 1, the results indicated that increments of impervious surfaces positively correlate with peak flows and flooding. The incidence is higher at the initial state of urban development. The imperviousness in the area grew from 25% in 2003 to 57% in 2013.

Moreover, scenario 2 proved that even with lower rainfall intensities in the future due to climate change, the network system still overloads. Therefore, a proposal was designed to determine the efficiency of implementing sustainable urban drainage systems (SUDS). It was confirmed by the model that through green roofs (GR) or permeable pavements (PP) as adopted solutions, peak flow and flooding reduce, as well as the overloaded elements. PPs had a better efficiency, with a 9,70% reduction in peak flow and 36% in flooding. While GRs had 2% and 22%, respectively. The results were discussed with a former and current municipality official, finding them beneficial for urban planning. However, it requires confronting issues related to institutional, monetary, planning and risk management to implement them. Still, this study provides valuable guidance for practitioners and public administrators, as it includes criteria for addressing potential risks due to drainage network performance. Furthermore, such results can help to assess areas located on risk zones to activate prevention measures and predict probable disaster events related to overloaded systems.