Impacts of Changes in Climatic Conditions and Urbanization on Runoff at City Scale

Urbanization and climate change are increasingly recognized as key drivers of hydrological alterations in rapidly growing cities. This study assesses their combined and individual impacts on runoff generation in Algiers, Algeria, over the period 1992–2016 using the Soil Conservation Service Curve Number (SCS-CN) model. Land cover maps from the European Space Agency’s Climate Change Initiative and long-term rainfall records were integrated with hydrological soil data to quantify runoff under three scenarios: (i) real conditions combining changes in climatic conditions and urbanization, (ii) fixed urban settings isolating climate effects, and (iii) fixed climatic conditions isolating urbanization impacts. Findings reveal that during the period 1992-2016, the city experienced an expansion of the impervious surfaces (from 19.86% to 41.48%) at the expense of other land covers. Moreover, the results show that although annual precipitation remained close to its baseline (608.25 mm/y), runoff displayed a continuing upward shift above its baseline (70.04 mm/y) after the early 2000s. Correlation analysis indicates that precipitation highly affects runoff variability (R² = 0.695) compared to urbanization impacts. Nevertheless, under the fixed climate conditions scenario, the 2-fold urban area expansion (with an increase of +108.4%) between 1992 and 2016 led to a +11.9% increase in runoff, underscoring its structural role in altering hydrological responses. These findings highlight the dual influence of the climatic conditions and land-use change on urban runoff dynamics and emphasize the need for integrated planning to enhance flood resilience and sustainable water management.