Long-Term Water and Energy Fluxes Observation in a Moist Tropical Forest in Vietnam

Abstract:

Evapotranspiration and energy fluxes for eight years (2012–2019) on the first in Vietnam eddy covariance site above a mature mixed moist tropical forest were measured. The fluxes were sampled at 10-Hz frequency using an open-path infrared gas analyser (LI-7500A, Li-Cor Inc., USA) and a 3-dimensional sonic anemometer (CSAT3, Campbell Scientific Inc., USA). Gaps in the fluxes were filled using the updated lookup table method (Falge et al., 2001; Reichstein et al., 2005) in the REddyProcWeb online tool, Max Planck Institute for Biogeochemistry, Germany (Wutzler et al., 2018). The wide range of climate variation connected to El Niño oscillation was recorded. Two dry seasons were dryer than the average (during the El Niño events of 2016 and 2019) and the other two dry seasons were rainy (during the La Niña events of 2012 and 2017). In the second half of the dry season of 2016 the volumetric soil water content dropped to 10 % and noon-time air temperature in the canopy rised to 40 degrees Celsium. Sensible heat flux was twice higher than the latent heat flux. Vice versa, dry season of 2017 has the extrordinary high precipitation and the monthly mean sensible heat flux not exceeded the latent heat flux. The measurements did not show much variations in annual net radiation (CV = 3%), a bit versatile were E (7%), VPD (8%) and precipitation (10%). In summary, El Niño and La Niña years may be considered as two extreme regimes of dry-season humidity and temperature for the studied forest. La Niña years had ultimately full-year per humid conditions. Even in El Niño-related drought, evapotranspiration of the studied ecosystem persisted at a relatively high level, preventing overheating of the atmospheric boundary layer.