Multi-satellite derived data reveals spatiotemporal dynamics of carbon-water coupling and its drivers in tropical ecosystems

Abstract

Climate change has significantly impacted tropical water use efficiency (WUE), defined as the ratio of gross primary productivity (GPP) to evapotranspiration (ET). However, the spatiotemporal dynamics and controlling factors of WUE in these regions—particularly the effects of extreme El Niño events—remain unclear. Using multiple satellite-derived GPP and ET datasets with large-scale observations, here we quantified WUE trends from 2001 to 2020 and assessed the impact of the 2015/16 El Niño drought on WUE in the tropics. Our analysis revealed a significant upward trend in tropical WUE, increasing at a rate of 0.007 ± 0.001 g C kg⁻¹ H₂O yr⁻¹ (mean ± standard deviation), with the largest increase observed in tropical Asia (0.01 ± 0.001 g C kg⁻¹ H₂O yr⁻¹). Spatially, three independent remote sensing-driven datasets consistently showed a significant WUE increase in 32%–54% of tropical regions, while only 1%–3% experienced a significant decline. Furthermore, tropical ecosystems exhibited a substantial increase in GPP (5.47 ± 0.60 g C m⁻² yr⁻¹), with the highest growth rate in tropical Asia (11.45 ± 0.37 g C m⁻² yr⁻¹), whereas ET showed minor changes. This suggests that WUE changes in tropical ecosystems are primarily driven by increases of GPP rather than ET. Further analysis identified leaf area as the dominant factor influencing WUE, GPP, and ET trends across the tropics. We also found that the extreme drought during the 2015/16 El Niño event resulted in a net decrease in WUE (−0.03 ± 0.01 g C kg⁻¹ H₂O), which transitioned to a net increase (0.04 ± 0.01 g C kg⁻¹ H₂O) by 2016/17. Compared to satellite-driven results, most land surface models captured the direction of tropical WUE trends but simulated a slower rate of change, with substantial variation in predicted trend intensities among models. This study advances our understanding of tropical ecosystem WUE dynamics and provides critical insights for predicting future WUE changes under ongoing climate change, informing strategies for carbon sequestration and water resource management in vulnerable tropical regions.