Trait-based representation of hydrological functional properties of plants in weather and ecosystem models

Land surface models and dynamic global vegetation models typically represent vegetation through coarse plant functional type groupings based on leaf form, phenology, and bioclimatic limits. Although these groupings were both feasible and functional for early model generations, in light of the pace at which our knowledge of functional ecology, ecosystem demographics, and vegetation-climate feedbacks has advanced and the ever growing demand for enhanced model performance, these groupings have become antiquated and are identified as a key source of model uncertainty. The newest wave of model development is centered on shifting the vegetation paradigm away from plant functional types(PFTs)and towards flexible trait-based representations. These models seek to improve errors in ecosystem fluxes that result from information loss due to over-aggregation of dissimilar species into the same functional class. We advocate the importance of the inclusion of plant hydraulic trait representation within the new paradigm through a framework of the whole-plant hydraulic strategy. Plant hydraulic strategy is known to play a critical role in the regulation of stomatal conductance and thus transpiration and latent heat flux. It is typical that coexisting plants employ opposing hydraulic strategies, and therefore have disparate patterns of water acquisition and use. Hydraulic traits are deterministic of drought resilience, response to disturbance, and other demographic processes. The addition of plant hydraulic properties in models may not only improve the simulation of carbon and water fluxes but also vegetation population distributions.

Evaporation and CO_(2)fluxes in a coastal reef:an eddy covariance approach

Introduction:We conducted season-long observations of evaporation and carbon flux at the Gulf of Aqaba coast,northern Red Sea.We used the eddy-covariance method with a two-tower setup to measure evaporation rates over land and sea and the advection between them.Using a three-dimensional mass balance approach,we calculated total evaporation as the sum of two main components in our site:horizontal advection and turbulent vertical flux,with half-hourly change of water vapor storage and horizontal flux divergence found to be negligible.Outcomes:Average evaporation rates were 11.4[mm/day]from April through May(early summer)and 10.5[mm/day]from June through August(summer).The coastal reef was a CO_(2)sink over the period of measurements,significantly higher in June through August than in April through May.The main environmental drivers of CO_(2)flux were humidity,water temperature,sensible heat flux,and wind speed.Discussion:The rates of evaporation near the shore were considerably higher than values reported in other studies typically used to represent the mean for the whole Gulf area.We found that evaporation rates computed by common bulk models approximate the mean values of evaporation but have poor representativeness of the intra-daily temporal variation of evaporation.There was a significant correlation between CO_(2)flux and evaporation attributed to common environmental drivers of gas diffusion,turbulent fluxes,and horizontal transport.Conclusion:We conclude that observations of fluxes in coastal waters need to use at least a two-tower system to account for the effect of horizontal advection on the total flux.