Work

Free satellite data and open-source tools for urban green spaces and temperature pattern analysis in Algiers

Year: 2025

Type: article

Abstract: • Algiers experienced increasing urbanisation and decreasing urban green spaces (UGSs) between 2004 and 2022. • Integration of static landscape metrics and dynamic Land Surface Temperature (LST) trends showed persistent warming trends. • Analysis of landscape metrics identified 600 m as the optimal scale for assessing UGSs-LST relationships in Algiers. • The vegetation cover metric, PLAND, explained 61% of LST variability; larger, contiguous UGS enhanced cooling. • A novel open-source framework — PyQGIS LMs calculator, GEE and RStudio — facilitates analysis in resource-limited settings. Rapid urbanization and global climate change are intensifying the Urban Heat Island (UHI) effect in cities worldwide, with consequences for human health and well-being. Urban green spaces (UGSs) mitigate extreme temperatures, but their cooling potential depends on spatial configuration, size, shape, and distribution. This study fills a geographic gap by providing one of the first detailed analyses of UGSs-Land Surface Temperature (LST) dynamics in a North African context. It combines spatial pattern analysis with temporal trend detection to comprehensively evaluate UGSs-LST relationships in Algiers from 2004 to 2022, addressing a common limitation in the literature where these approaches are often treated separately. Using freely available satellite data and open-source tools—including Landsat data from Google Earth Engine (GEE), QGIS, and RStudio—we integrate supervised classification, landscape metrics (LMs) computation via our custom PyQGIS LMs calculator, and Mann-Kendall trend analysis to quantify the static spatial configuration of green spaces and their dynamic thermal impacts over time. Findings reveal a 38% decrease in green spaces and a 10% reduction in agricultural land, accompanied by increased urbanization. Strong negative correlations between some LMs and LST were observed, with PLAND (Percentage of Landscape) explaining 61% of LST variability at an optimal 600-meter scale. This medium-sized scale differs from previous findings in other regions, highlighting the importance of context-specific analysis. LST trend analysis identified specific heat-resistant zones characterized by large, contiguous green patches. Despite greening initiatives, UGSs in Algiers continue to decline, underlining the need to preserve and strategically expand UGSs to combat rising temperatures.

Source: International Journal of Applied Earth Observation and Geoinformation

DOI: 10.1016/j.jag.2025.104482

Authors: Nadia Mekhloufi, Mariella Aquilino, Amel Baziz, Chiara Richiardi, Maria Adamo