Projected Changes in SWA over the Main BRI Regions for Net-Zero and Net-Negative Future

Surface water availability (SWA, calculated by precipitation [P] minus actual evaporation [E]) has great impacts on society. However, it remains unclear how SWA will change in a net-zero and net-negative future. In this study, we examine future changes in P, E, and SWA from the Coupled Model Intercomparison Project Phase 6 (CMIP6) for net-zero (2050-2060) and net-negative (2090-2100) CO2 emissions periods under pathway SSP1-1.9 relative to historical baseline (1995-2014) in the main Belt and Road Initiative (BRI) regions. We also consider SSP2-4.5 and SSP5-8.5 for comparison. We find that P, E, and SWA changes exhibit obvious spatial heterogeneity, with increase or decrease over different areas for 2050-2060 and 2090-2100 relative to 1995-2014 under 3 scenarios. SWA changes are generally insignificant excluding some isolated areas under SSP1-1.9, yet have statistical significances over Central Africa and many areas in Eurasia for SSP2-4.5 and SSP5-8.5. Average monthly P and E are expected to markedly increase by 2.63 and 2.01 mm, 1.85 and 1.65 mm, for net-zero and net-negative periods under SSP1-1.9. Consequently, the projected monthly SWA will change by 0.78 and 0.36 mm. However, the projected P, E, and SWA have much larger changes in the same periods under the other 2 scenarios, especially 2090-2100. Our research provides previously unknown knowledge that SWA shows quite different changes in the net-zero and netnegative periods under SSP1-1.9 relative to the same periods under SSP2-4.5 and SSP5-8.5, which may facilitate management of water resource risks to ecosystems and human society.