| 05 Oct 2025
A synthesis of water, energy, and carbon fluxes sensitivity to climate variables in Southeast Asia
Abstract. Southeast Asia (SEA) plays an important role in the Earth’s carbon and water cycle, yet ecohydrology dynamics occurring in this region remain poorly understood due to the paucity of field observations and modelling studies. Here, we investigate water, energy, and carbon fluxes by combining existing flux tower data with mechanistic ecohydrological modelling for 20 sites. A sensitivity analysis to meteorological forcings is used to understand water and energy limitations. Results show large latitudinal differences but overall suggest a strongly energy-limited region, where evapotranspiration (ET) is tightly correlated with net radiation and is highly responsive to relative humidity. Gross primary productivity (GPP) is also correlated to net radiation and is most responsive to shortwave radiation changes. Only a few ecosystems in SEA show signs of water limitations, such as certain grasslands in the Tibetan plateau, savannas, and dry deciduous forests. We further disentangled the relative effect of warming and humidity changes in vapor pressure deficit (VPD). Sensitivity analysis indicates that climate warming-induced VPD changes – rather than pure warming – can have important effects on ET but the opposite is true for GPP with complex GPP responses to temperature based on the thermal photosynthetic optimum and phenological responses. Water use efficiency (WUE) is highly correlated with annual mean precipitation across space, but its responses to precipitation changes are less consistent and WUE changes are most sensitive to relative humidity. Carbon use efficiency (CUE) is more responsive to air temperature than other climate drivers. These insights quantify water, energy, and carbon fluxes in an underrepresented part of the Earth and enhance our understanding of how climate can modify carbon and water cycles in this region.
The manuscript by Ren et al presents an analysis of carbon and water fluxes at eddy covariance sites across South East Asia and their meteorological drivers from data and model simulations. While the study has potential, as it stand it falls extremely flat. I understand the author’s argument that such studies have not been done in SE Asia, as it stands it does not bring anything new to the field.
Even disregarding novelty, which could be argued is not an argument for publishing a paper, the manuscript is lacking in clarity and the analysis is simplistic. Specifically:
Specific comments
Table 2 – what si the source of these data?
L 218 “identify suitable parameters” more details are needed as to which parameters and how values were found
L 219 was the site level met data the only source used as input? Was the model run with repeated meteorology? Does it require spinup?
L 226 what does correlation analysis mean in this context? Assuming this si for the moel output since there are variables that cannot be measured at flux towers. More details needed
L 235 clarify, presumably each variable has the same units across sites
L 239 is this then the standard deviation of a standard deviation?
L 253 which variables were added/multiplied and which subtracted?
L 260 6 years is not enough time to initialise C pools, worth checking if all pools are actually in equilibrium
L 285 why did the authors not just partition the NEE, there out of the box packages to do this
Fig 2 worth also reporting other measures of fit, such as RMSE. It would also be useful to have the land cover for each site indicated on the plot
Fig 7-9 what are the different lines here? This is not described in the methods. Givent eh nature of the perturbation, if this is a regression line for each site it essentially amounts to drawing a line through 3 points
L 680 there should be a link to the flux data too