Tropical freshwater reservoirs are vital for water management but also contribute to greenhouse gas (GHG) emissions, making mitigation strategies crucial, especially in the Brazilian Northeast, where water scarcity and climate variability impact livelihoods and ecosystems. This semi-arid region depends on reservoirs due to irregular rainfall and high evaporation, with reforestation offering a promising means to offset emissions while supporting sustainable water management. We assessed the carbon footprint and offsetting potential of 24 small reservoirs in the region using the G-res tool under SSP2-4.5 and SSP5-8.5 climate scenarios. Results show that GHG emissions vary with water depth, climate, and land use, with smaller reservoirs often showing higher emissions. Expanding vegetation in catchments and around reservoirs can help offset emissions and enable blue-green transitions for climate change mitigation. Future reforestation efforts must increase significantly, requiring a 286% rise in forested areas compared with the reference period under the SSP5-8.5 scenario to fully offset emissions. By analyzing emissions from reservoirs and applying reforestation to reduce their carbon footprint, this study shows that (1) climate change and unsustainable transitions raise GHG emissions in tropical reservoirs, (2) reforestation can offset emissions and support sustainable management, and (3) future reforestation areas must expand under climate scenarios. HIGHLIGHTS center dot Climate change and unsustainable transitions boost greenhouse gas (GHG) emissions in tropical reservoirs. center dot Reforestation offsets reservoir GHG emissions and supports sustainable resource transitions. center dot Future reforestation areas in tropical reservoirs should expand under climate scenarios.