Rising atmospheric CO₂ concentration ([CO₂]) enhances photosynthesis and reduces transpiration at the leaf, ecosystem, and global scale via the CO₂ fertilization effect. The CO₂ fertilization effect is among the most important processes for predicting the terrestrial carbon budget and future climate, yet it has been elusive to quantify. For evaluating the CO₂ fertilization effect on land photosynthesis and transpiration, we developed a technique that isolated this effect from other confounding effects, such as changes in climate, using a noisy time series of observed land-atmosphere CO₂ and water vapor exchange. Here, we evaluate the magnitude of this effect from 2000 to 2014 globally based on constraint optimization of gross primary productivity (GPP) and evapotranspiration in a canopy photosynthesis model over 104 global eddy-covariance stations. We found a consistent increase of GPP (0.138 ± 0.007% ppm⁻¹; percentile per rising ppm of [CO₂]) and a concomitant decrease in transpiration (−0.073% ± 0.006% ppm⁻¹) due to rising [CO₂]. Enhanced GPP from CO₂ fertilization after the baseline year 2000 is, on average, 1.2% of global GPP, 12.4 g C m⁻² yr⁻¹ or 1.8 Pg C yr⁻¹ at the years from 2001 to 2014. Our result demonstrates that the current increase in [CO₂] could potentially explain the recent land CO₂ sink at the global scale.

Although Bornean tropical rainforests are among the moistest biomes in the world, they sporadically experience periods of water stress. The observations indicate that these ecosystems tend to have little regulation of water use, despite episodes of relatively severe drought. This water‐use behaviour is often referred to as anisohydric behaviour, as opposed to isohydric plants that regulate stomatal movement to prevent hydraulic failure. Although it is generally thought that anisohydric behaviour is an adaptation to more drought‐prone habitats, we show that anisohydric plants may also be more favoured than isohydric plants under very moist environments where there is little risk of hydraulic failure. To explore this subject, we examined the advantages of isohydric and anisohydric species as a function of the hydroclimatic environment using a stochastic model of soil moisture and carbon assimilation dynamics parameterized by field observations. The results showed that under very moist conditions, anisohydric species tend to have higher productivity than isohydric plants, despite the fact that the two plant types show almost the same drought‐induced mortality. As precipitation decreases, the mortality of anisohydric plants drastically increases whereas that of isohydric plants remains relatively constant and low; in these conditions, isohydric plants surpass anisohydric plants in their productivity.

Nature‐based solutions for water‐resource challenges require advances in the science of ecohydrology. Current understanding is limited by a shortage of observations and theories that can further our capability to synthesize complex processes across scales ranging from submillimetres to tens of kilometres. Recent developments in environmental sensing, data, and modelling have the potential to drive rapid improvements in ecohydrological understanding. After briefly reviewing advances in sensor technologies, this paper highlights how improved measurements and modelling can be applied to enhance understanding of the following ecohydrological examples: interception and canopy processes, root uptake and critical zone processes, and up‐scaled effects of land use on streamflow. Novel and improved sensors will enable new questions and experiments, while machine learning and empirical methods provide additional opportunities to advance science. The synergy resulting from the convergence of these parallel developments will provide new insight into ecohydrological processes and thereby help identify nature‐based solutions to address water‐resource challenges in the 21st century.