Sudden changes in heatwave patterns have become a significant health concern for the inhabitants of South Asian Countries (SACs) since 2020. While this abnormal phenomenon indicates a rapidly increasing trend of greenhouse gases (GHGs), awareness and understanding of the issue remain limited in most SACs. This systematic review aims to identify potential methane hotspots in landfill sites across SACs and assess the impact of methane emissions on regional heatwaves. Based on existing research, 44 potential methane hotspots were identified in landfill sites across SACs, with most sites located in India, Pakistan, and Bangladesh. The observed methane emissions ranged from 41.41 to 1.48 Gg/year in India, 55.93–0.27 Gg/year in Pakistan, and 25.95–24.97 Gg/year in Bangladesh. This study also revealed that a significant volume of methane is dispersed transboundary, affecting Afghanistan, Nepal, and Bhutan due to emissions originating from neighboring countries, including Pakistan, Iran, Turkmenistan, India, and China. Notably, a positive correlation (p < 0.05, R² = 0.77) was found between methane concentrations in SACs (India, Pakistan, and Bangladesh) and rising heatwave temperatures. Lastly, given the significant energy potential of landfill sites in SACs, this study recommends implementing waste-to-energy plant technology as a strategic approach to achieve Sustainable Development Goal 7 (SDG-7).