Diverging estimates of future global wetland areas under warming scenarios

Despite its critical importance in the global cycles of energy, water, and carbon, the extent of global wetlands remains highly uncertain. A straightforward approach to estimating global wetland areas is to relate the topographic wetness index (TWI) with groundwater or climate variables. In this study, we examined multiple TWI-based methods for estimating wetland areas across historical and future timeframes. First, we identified inland wetlands using global TWI data combined with soil moisture data from an advanced reanalysis system. For comparison, we also generated three other sets of wetland area estimates using monthly precipitation and potential evaporation (E_p) data from the same system, applying three different E_p formulas to assess the sensitivity of wetland areas to changes in surface resistance. We extended this methodology to multiple Earth system models (ESMs) from the Coupled Model Intercomparison Project phase 6 (CMIP6) to explore the impact of atmospheric CO₂ concentrations on wetland dynamics. Our findings indicated that increases in historical atmospheric CO₂ had a minimal impact on TWI-based wetland areas. However, their influence is expected to become more significant even under a sustainable emission scenario by the mid-2050s. We also found that CMIP6 ESM soil moisture projections show smaller changes in wetland areas compared to those estimated using a traditional E_p formula. This highlights potential inconsistencies between future wetland projections based on climatic variables and those derived from soil moisture projections.

Acknowledgements: This work was supported by Korea Environmental Industry & Technology Institute (KEITI) through Wetland Ecosystem Value Evaluation and Carbon Absorption Value Promotion Technology Development Project (2022003640001), funded by Korea Ministry of Environment (MOE).