Coastal river deltas are among the world’s most vulnerable regions to climate change, hosting dense populations on low-lying, subsiding land. This chapter examines climate risk modeling and scenario analysis applied to a data-rich Indian delta, focusing on the Ganga–Brahmaputra delta (GBD). We present a theoretical framework for climate risk, integrating hazard (sea-level rise, cyclones, floods), exposure, and vulnerability, and outline modeling tools such as hydrologic SWAT models, 3D hydraulic surge models (e.g. Delft3D/SWAN), and GIS-based flood mapping. Using recent hydrologic projections (RCP4.5/8.5 scenarios) and idealized sea-level rise (SLR) increments (0–1.5 m), we simulate flood extents under multiple scenarios. Results indicate dramatically increased flood risk: for example, a 1.5 m SLR raises cyclone-flood inundation from ~ 12 to 33% of coastal Bangladesh. Hydrologic SWAT modeling shows Brahmaputra flows and water yields rising ~ 8% under mid-century RCP scenarios. Scenario comparisons reveal that extreme events will become more frequent (e.g. a 61-year flood becomes an 11-year event) and high-flood zones expand significantly. We also evaluate nature-based solutions (NbS)—such as sediment management, restored floodplains, mangrove buffers, and tidal river management—as complementary adaptations. A sediment-focused analysis shows that enhanced natural sediment delivery (e.g. under stronger monsoons) could offset relative sea-level rise, whereas large dams or diversions would reverse these gains. These findings are discussed in light of policy and Sustainable Development Goals (SDGs), emphasizing that sustaining sediment supplies and ecosystem functions is critical for delta resilience. The chapter concludes with recommendations for integrated climate-risk models and multi-scenario planning that prioritize NbS and SDG-aligned adaptation in Indian deltas.