Transboundary deforestation and flood risk: Assessing the need for collaborative policy between India and Nepal’s Siwalik regions

• Assesses transboundary deforestation and flood risk in India–Nepal’s Siwalik regions. • Links forest loss to increased soil erosion, runoff, and flood vulnerability. • Reviews policy gaps and challenges in cross-border forest management. • Proposes a collaborative framework for joint conservation and risk reduction. • Emphasizes community and international cooperation for sustainable solutions. The Siwalik foothills of India and Nepal have experienced environmental deterioration due to deforestation, which has now increased flood risks throughout both nations. The flood hazard in this region has become more severe over the past twenty years. This research examines the impact of forest area modifications affect flood occurrences in the Siwalik ecological zone spanning across two countries from 2001 through 2023 by combining spatial data with statistical models of heavy rainfall and historical flood records. The research shows that every 1% decrease in forested land results in an 18.5-30.7% increase in flood occurrences, which exceeds global averages by two to three times, thus demonstrating the Himalayan region's heightened sensitivity. The findings highlight that deforestation, coupled with the region’s fragile geomorphology and monsoon variability, is a critical driver of flood hazards. Despite policy efforts in both India and Nepal, fragmented governance and weak cross-border coordination hinder effective responses. The study emphasizes the urgent need for a harmonized transboundary policy framework that integrates community participation, equitable benefit-sharing, and adaptive governance to mitigate risks and foster long-term ecological sustainability.