Modulation of Land Photosynthesis by the Indian Ocean Dipole: Satellite-Based Observations and CMIP6 Future Projections

Indian Ocean Dipole (IOD), a major climate variability in the tropics which drives the abiotic stress associated with heavy rainfalls and severe droughts, is not much understood in terms of its role in the carbon cycle, while El Niño-Southern Oscillation (ENSO)-related terrestrial carbon cycle variation has been intensively studied. Here, we investigate IOD's impact on land photosynthesis over the Indian ocean rim countries during austral spring using satellite-based gross primary productivity (GPP) and Earth System Model simulations produced in the Coupled Model Intercomparison Project Phase 6 (CMIP6). IOD independently affects GPP with significant positive partial correlation coefficients (pcor) over most of Africa and India, and negative pcor over southern China, Indo-China peninsula, maritime continent, and Australia, mostly driven by precipitation variations; this obviously differs from the widespread significant negative pcor pattern induced by ENSO. The recent extremely positive IOD in 2019 caused the canonical IOD-affected GPP patterns, however, with its extreme impacts. Furthermore, though large inter-model spreads exist, the CMIP6 multimodel median can basically capture the main characteristics of IOD-affected precipitation and GPP patterns. Importantly, IOD is predicted to occur more frequently in future warming scenarios. Model future projections suggest that it will exert larger impacts on GPP variations over central and eastern Africa, Sumatra, western and southeastern Australia with stronger pcor and enhanced explained variance, but less impacts over southern Africa, east India, Indo-China peninsula, and northeastern Australia. Therefore, besides ENSO, understanding the IOD impacts can provide us new insights into regional and global carbon cycle interannual variability.