Decarbonizing Pakistan’s transport sector: insights from water-energy nexus simulation by LEAP-WEAP integrated model

• Pakistan struggles with urbanization-driven energy and water shortages. • New LEAP-WEAP Nexus model is developed to analyze urban transport systems’ interplay. • Electric vehicle transition may strain water resources. • Policies: mass transport, hydrogen, HCNG tech for balanced footprint. • Managing energy-water-carbon nexus is key for sustainable strategy. Pakistan, the fifth most populous country globally, has been grappling with severe water and energy shortages for decades. Rapid urbanization and population growth, coupled with inefficiencies in the energy and water sectors, have intensified the nation’s resource security. Among all sectors, transportation and domestic use have emerged as major contributors to excessive consumption. In response, this study adopts a systems-thinking approach focused on the transportation sector, employing an integrated water–energy–carbon nexus framework to inform sustainable policy pathways. The analysis is conducted by coupling the LEAP and WEAP models under four scenarios: Business as Usual (BAU), Electric Vehicles Scenario (EVS), Hybrid Vehicles Scenario (HVS), and Mass Transportation Scenario (MTS). Results indicate that a transition towards electric and hydrogen-powered transport can reduce carbon emissions but places additional pressure on national water resources due to the water-intensive nature of power generation and hydrogen production. By 2050, water demand under the EVS, HVS, and MTS scenarios is projected to reach 152 MCM, 123 MCM, and 102 MCM, respectively. In terms of emissions, MTS achieves the lowest carbon output at 92 MtCO 2 eq, followed by 178 MtCO 2 eq (HVS), 316 MtCO 2 eq (EVS), and 481 MtCO 2 eq (BAU). These findings reveal critical trade-offs: while electric and hybrid vehicle adoption can substantially mitigate greenhouse gas emissions, they may exacerbate water scarcity, particularly under thermoelectric and hydrogen-reliant energy mixes. Conversely, the MTS scenario demonstrates clear synergy by minimizing both water consumption and emissions, highlighting its dual mitigation potential. The study concludes that addressing Pakistan’s climate and resource security challenges demands an integrated nexus-based approach, one that combines mass transit expansion, alternative fuel adoption, electrification, and water conservation measures to ensure a sustainable and resilient transportation future.