Main environmental driver and seasonality of water use efficiency in tropical forests

Abstract

This study investigates Water Use Efficiency (WUE) in tropical forests, emphasizing the principal environmental drivers and their seasonal variations. Tropical forests play a pivotal role in global carbon and water cycles; however, the dominant environmental drivers influencing tropical forest WUE and its seasonal differences remain inadequately understood. Using simulations from terrestrial biosphere models covering the period from 1901 to 2010, this research reveals that (i) WUE increased in 98.9 % of tropical forests, with an average increase of 0.318 g C kg H₂O^–1 over this period, (ii) the average contributions of elevated CO₂, climate change, nitrogen deposition, and land cover change to WUE variations in tropical forests were 82.02 %, 5.64 %, 11.64 %, and 0.69 %, respectively, (iii) 83.5 % of tropical forests experienced an increase in WUE of more than 0.1 g C kg H₂O^–1 per year under the influence of elevated CO₂, with a smaller positive contribution from nitrogen deposition, while land cover change and climate change had negative impacts on WUE in 63.8 % and 59.2 % of tropical forests, and (iv) average tropical forest WUE during the dry season was 0.719 g C kg H₂O^–1 higher than that in the wet season, with the increasing trend of CO₂ and the interannual variability of climate change being the primary factors influencing WUE changes at the per-grid level. This study enhances our understanding of the dynamics of carbon and water cycles in tropical forests during periods of varying water availability and provides essential insights for predicting future shifts in tropical forest WUE under global change.