The Green Area Ratio as a planning tool for sustainable green infrastructure in a highly dense and arid urban environment. : case study Lima, Peru

Abstract

Green infrastructure (GI) can simultaneously deliver a wide range of highly beneficial ecosystem services (ESs) for cities. However, in densely built arid environments, implementing GI can worsen water scarcity, limiting its effectiveness as a climate change mitigation measure, especially against urban heat islands (UHIs). The Green Area Ratio (GAR) could be a helpful tool to determine the proportion of functional GI to overcome these issues. However, the tool has been not explored in arid contexts.

Based on the revision of nine existing GAR tools, this thesis determines whether any is suitable for implementation in arid environments, using Lima, Peru as a study case. Lima is a dense megacity with extremely low rainfall, increasing temperatures and scarce green areas. On the basis that none had prioritised water conservation to achieve thermal regulation, a new tool was developed based on scientific evidence and a microclimate analysis with ENVI-met.

The creation of the tool, the GAR Lima, showed that despite aridity, the presence of GI is relevant for Lima´s sustainable development and resilience. However, there is a need to combine it with other surfaces and supporting infrastructure to become sustainable. Such complexity suggests GI should not be considered the main resource to overcome environmental challenges in an arid city and therefore other sustainability approaches should be considered. The application of the tool indicates that arbitrarily increasing the ratio of GI in Lima may not necessarily lead to an improvement of the urban quality, even if it is designed under Xeriscape design principles. Xeriscape may not always result in a higher functionality as some surface combinations may not always result beneficial for thermal regulation, UHI mitigation and further ESs.

While this demands thorough testing, the GAR Lima nevertheless represents a preliminary evidence-based framework for better understanding of how to maximise the ESs delivered by GI in densely built arid urban areas. It is, therefore, a basis for potential implementation.