Eco-hydrological characterisation of nature-based solutions (NbS) for urban heat island (UHI) effect regulation: assessing the long-term thermal performance of live pole drains (LPDs)

Nature-based Solutions (NbS) for stormwater management (SM) are receiving considerable attention due to their relevant eco-hydrological functions and their potential to mitigate urban heat island (UHI) effects by promoting evapotranspiration. An innovative approach within the NbS-SM umbrella is the Live Pole Drain (LPD). This plant-based drainage system consists of live fascine bundles placed in shallow trenches. LPDs can be constructed using locally available materials and hand tools, making them ideal for draining surface water in areas with limited space and resources. Despite its practical applications, the eco-hydrological performance of LPDs functioning as micro-urban cooling solutions remains poorly researched and understood. This study aims to evaluate the long-term thermal performance of LPDs by investigating the impacts of seasonal fluctuations on LPDs' energy and water mass balance, which ultimately affects evapotranspiration and latent heat fluxes. To achieve this, we established LPD and fallow soil (i.e. control) treatments on an artificial mesoscale slope in an open-air laboratory (OAL). We monitored soil temperature and moisture over 1+ years using environmental sensors to estimate latent heat fluxes derived from evapotranspiration. Preliminary results showed that LPDs maintained lower moisture content than fallow soil due to lateral drainage of excess water, plant water uptake and evapotranspiration. While LPDs exhibited similar soil temperatures to fallow soil over the year, the vegetated system maintained a lower temperature during drought periods, reaching a peak difference of 12°C compared to fallow soil. Further analysis of this empirical research will determine LPDs' evapotranspiration and latent heat flux contributions, ultimately demonstrating their cooling potential. This research aims to provide a solid foundation for future studies, enhancing our understanding of the eco-hydrological performance of LPDs at the plot scale. It will further support their design and scalability for effective surface water drainage and improved outdoor thermal comfort.