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.