Multiscale analysis of statistical trends in water quality across land use gradients in the Najafgarh Drain, Delhi

Aquatic systems are known to be affected by LULC prevailing in their proximity at various spatial scales and configurations. This study investigates such associations for the Najafgarh drain in the Delhi megacity (Northern India) at two spatial scales (reach and riparian) and two seasons (pre- and post-monsoon) for the year 2019. LULC mapping within a 5 km buffer of the drain, conducted using on-screen visual interpretation, revealed a dominance of built-up areas (46.8%) followed by fallowland (27.3%), together comprising 74% of the total area. A comparison with 1999 data indicated a 20.5% increase in built-up areas over two decades, primarily replacing agriculture, fallowland, and vegetation. To examine LULC–water quality relationships, reach and riparian scale buffer analyses of varying widths were delineated, and landscape metrics were derived using FRAGSTATS. Statistical analyses, including Pearson correlation, principal component analysis, and multiple regression, showed that most of the water quality variables were positively correlated with built-up areas and negatively correlated with agriculture and fallowland. These associations became more pronounced with increasing buffer width, especially in the post-monsoon season. Reach-scale buffers effectively captured localized pollutant sources, while riparian-scale buffers were more useful for broader area management. The expansion of built-up areas and corresponding decline in natural and semi-natural land covers over 1999–2019 highlights the intensity of urban development in Delhi. This study provides a valuable database for policymakers and stakeholders involved in managing and improving water quality in urban aquatic systems such as the Najafgarh drain.