Quantifying the contribution of diminishing green spaces and urban sprawl to urban heat island effect in a rapidly urbanizing metropolitan city of Pakistan

Abstract

Sustainable urban land-use development and management practices are imperative to ensure the quality of the living environment. Unplanned expansion and densification of the urban area tend to imbalance the ratio of impervious surface to green spaces, resulting in the Surface Urban Heat Island (SUHI) effect. Land Use Land Cover changes, anthropogenic activity, and a sustainable future environment are all intertwined. This study aims to analyze urban policies impacts by quantifying built-up land, green spaces and their associated SUHI effects in the Lahore district of Pakistan. We used a tri-temporal medium resolution remote sensing imagery (2003, 2010 and 2019) and a long-term low resolution (1 km) Land Surface Temperature (LST) time series (2001–2020) to evaluate the impacts of the LULC changes on SUHI. We found rapid urban development in the study area over the last two decades (2003 - 2019) that resulted in the losses (36%) and gains (16%) in urban vegetation at the Union Council (UC) level. Spatial patterns showed the inconsistent distribution of green spaces across the study area. Large green spaces exhibit 1 to 4 °C lower LST compared to their surrounding built-up land. The overall green spaces were reduced from 15215 ha in 2003 to 10528 ha in 2010 and a total loss of ~19% was recorded in agricultural land and open spaces during 2003–2019. Nonetheless, it showed a recovery during the last decade with a current extent of 12316 ha in 2019. This increase in green space areas is due to the rising awareness about the significance of urban green spaces and nationwide plantation drives programs which help to mitigate SUHI effect. On the other hand, transition zones under development phase consisting of sand/vacant and barren land exhibit a mean 3-4 °C higher LST while the old city areas, including the walled city, continuously exhibit 1-2 °C higher LST from the average LST of the district which triggered the SUHI pockets formation. These results of the study highlight the importance of devising effective policies to monitor unprecedented urban sprawl and the reduction in the cooling effect because of disappearing vegetation particularly in old city areas and transition zones. However, the effective implementation of the urban land use policies should be ensured through institutional strengthening, adequate resource allocation, efficient procedures, and continuous geospatial monitoring for a better living environment and to combat climate change.