Assessing Hydro-ecological Restoration for Climate-resilient Flood Management in Large River Basins under growing Anthropogenic Pressures

Rising anthropogenic disturbances to forests and wetlands are intensifying hydrometeorological extremes under climate change, elevating socio-economic and environmental risks, particularly in developing regions with limited resilience. Floods, accounting for nearly 40% of global disasters, are highly sensitive to land-use change and shifts in climate regimes, with their frequency projected to double by 2030. The Brahmaputra River catchment in the Himalayan region exemplifies this growing crisis, which is highly vulnerable to prolonged and recurrent flooding, causing severe disruptions for millions of people. Over the last two decades, the basin has experienced rapid urbanization (~70%), notable forest loss (~3%), and drastic wetland decline (~80%). Using Cellular Automata-based LULC projections, this study finds an additional 3% decline in forest cover by 2050 may further exacerbate regional flood hazards. Although recent studies highlight the role of Nature-based Solutions (NbS) in urban flood management, there remains limited understanding of integrated multi-NbS strategies in large river basins. This study evaluates the restoration of forest and wetland cover to 2000-year levels using a coupled hydrological-hydrodynamic modeling framework. Future climate impacts were assessed using multi-criteria-evaluated, downscaled, and bias-corrected GCM projections. While GCM-based simulations improve understanding of NbS performance under extreme conditions, the socio-economic implications of restoring ecosystems remain insufficiently explored.

In the present study, the peak streamflow is projected to increase by 5-6% in upstream sub-basins and by 2-3% downstream under the worst-case LULC-2050 scenario. Forest restoration beyond 85% cover in any sub-basin showed diminishing hydrological benefits, whereas moderate restoration in areas with less than 70% forest cover was more effective. Similarly, natural or unmanaged wetlands were observed to be insufficient for flood mitigation due to early monsoon saturation. Implementing a hydro-ecological-based wetland management strategy by draining partial storage before storm events significantly enhanced the wetland retention capacity and provided greater peak-flow reduction than forest restoration alone. Combined restoration measures lowered the peak flows below historical (1991–2020) levels at major cities of the region, i.e., Dhubri (3%), Tezpur (2.7%), Guwahati (2.3%), and Dibrugarh (1.5%). Return-period analysis revealed that a 25-year flood at Dhubri could shift to a 60-year event with integrated restoration but worsen to a 10-year event by 2050 without wetland management. Flood exposure in built-up and agricultural areas is expected to rise by 3.5% and 8%, respectively. However, restoration could lower these exposures by about 2% and 5%, which could protect 1.6 million people. Overall, the findings demonstrate that targeted ecosystem restoration and sustainable hydro-ecological management can substantially enhance flood resilience in large river basins and serve as effective NbS for climate change adaptation.