Aims:
Rapid urbanization, the expansion of built-up areas, and the increasing proportion of impervious surfaces have significantly altered natural hydrological processes in cities. These transformations reduce rainfall infiltration, increase the volume and velocity of surface runoff, and place increasing pressure on conventional urban drainage systems. Traditional stormwater-management approaches are primarily based on the rapid collection and conveyance of runoff through drainage networks. Although these systems can reduce temporary water accumulation, they do not necessarily contribute to restoring the natural urban water cycle and may transfer runoff pressure to downstream areas. In response to these limitations, the sponge city approach has emerged as an integrated framework for managing urban rainwater through infiltration, retention, detention, storage, controlled conveyance, and reuse. Blue–green infrastructure constitutes one of the main spatial components of this approach by integrating hydrological functions with green spaces, permeable surfaces, water corridors, and urban open spaces. However, the need for such interventions is not spatially uniform. Differences in topography, runoff concentration, surface imperviousness, soil characteristics, green cover, and land use create different levels of intervention priority. Therefore, this study aimed to identify and zone priority areas for blue–green infrastructure interventions for flood management based on the sponge city approach in the northeastern zone of Tabriz.
Materials and Methods:
This study was applied in purpose and descriptive–analytical in method. The study area covered the northeastern zone of Tabriz and included Khalilabad, TarlanDarasi, Idehloo, Ghooshkhaneh, MollaZeinal, and Ahmadabad neighborhoods. An integrated framework combining the Analytic Hierarchy Process (AHP) and Geographic Information System (GIS) was employed to determine spatial intervention priorities. Six criteria were selected according to their influence on urban runoff processes and their relevance to sponge-city interventions: surface imperviousness, terrain slope, flow accumulation, hydrological soil group, green cover, and land use. The corresponding spatial layers were prepared and processed in GIS and standardized to establish a common analytical scale. Higher flow accumulation and surface imperviousness were associated with greater intervention priority, whereas lower green cover indicated a greater need for intervention. Terrain slope and hydrological soil groups were reclassified according to their effects on runoff movement and infiltration potential, while land-use classes were evaluated according to surface characteristics and runoff-generation potential. The relative importance of the criteria was determined through AHP pairwise comparisons. The Consistency Ratio (CR) was calculated to assess the internal consistency of the comparison matrix, and CR < 0.10 was considered acceptable. Finally, AHP-derived weights were assigned to the standardized layers and integrated through weighted spatial overlay in GIS to calculate the Blue–Green Infrastructure Priority Index (BGIP). The resulting index was classified into five intervention-priority levels: very low, low, moderate, high, and very high.
Findings:
The AHP analysis demonstrated that the six criteria did not contribute equally to the spatial priority of blue–green infrastructure interventions. Flow accumulation obtained the highest weight (0.286) and ranked first, indicating the major role of runoff concentration in determining intervention priority. Surface imperviousness ranked second with a weight of 0.238, reflecting the importance of surface sealing and reduced infiltration in runoff generation. Terrain slope ranked third with a weight of 0.167, emphasizing the role of topographic conditions in controlling runoff movement. The hydrological soil group received a weight of 0.135, while green cover and land use obtained weights of 0.103 and 0.071, respectively. The first three criteria collectively accounted for 69.1% of the total model weight, demonstrating the dominant influence of runoff concentration, surface imperviousness, and topography on the spatial pattern of intervention priority. The Consistency Ratio was 0.068 (CR = 0.068), which was below the acceptable threshold of 0.10, confirming acceptable consistency in the AHP pairwise comparison matrix. The final BGIP zoning revealed considerable spatial differentiation across the study area. Overall, 43.3% of the study area, equivalent to 606.6 ha, was classified within the high and very high intervention-priority classes. These results indicate that the need for blue–green infrastructure is concentrated in specific spatial zones rather than being uniformly distributed throughout the northeastern zone of Tabriz.
Conclusion:
The study demonstrates that implementation of the sponge-city approach in the northeastern zone of Tabriz requires a transition from conventional, drainage-oriented stormwater management toward spatially targeted, decentralized, and integrated blue–green infrastructure planning. The integration of AHP and GIS provided a spatial decision-support framework through which hydrological, topographic, physical, and environmental characteristics could be evaluated simultaneously. The main scientific contribution of the research is the conversion of the sponge-city concept from a general urban water-management approach into a spatial framework for determining intervention priorities. The resulting BGIP zoning can assist planners in identifying areas where blue–green measures should be considered first and can provide a basis for subsequent site-specific selection of interventions such as rain gardens, bioswales, permeable surfaces, green drainage corridors, and temporary retention spaces. Nevertheless, the model determines spatial intervention priority rather than the exact type, size, or technical design of individual measures. Its results are also influenced by the accuracy of spatial data and expert-based AHP weighting. Future studies can therefore combine this framework with detailed hydrological simulations and site-scale analyses. Overall, the findings confirm that targeted blue–green infrastructure based on spatial priorities can provide an effective basis for integrated rainwater management and the implementation of sponge-city principles in the northeastern zone of Tabriz.