Evaporation from a Canadian west coast douglas-fir forest : seasonal patterns and controls
Notice bibliographique
Résumé
In order to understand how forest functioning will respond to global climate change, longterm and direct measurements of water vapour and energy exchange over forested ecosystems are needed. Between October 15, 1997 and May 31, 1999, eddy covariance measurements of latent and sensible heat flux were made above a 50-year-old, 33-m tall Douglas-fir forest, part of the seasonal temperate rainforest located on Vancouver Island, B.C, on the west coast of Canada. Winters at this site are wet and mild while summers are warm and dry. Evaporation rates and energy exchange varied widely on annual, seasonal and diurnal time scales and were used to discern the processes involved in the evaporation of water from this forest canopy. Ultimately, these variations were integrally linked to the canopy wetness and the surface conductance. Spectral analysis and turbulence characteristics were used to ensure measurement quality during inclement weather. The Gill Model 1012R2A sonic anemometer-thermometer used in this study performed well up to rainfall intensities of 4.6 mm h⁻¹. However, signal attenuation of the water vapour mixing ratio was observed during high humidity conditions due to water vapour adsorption/desorption effects on the sampling tube walls leading to the infrared gas analyzer. Total latent heat flux losses of up to 38% could be corrected using the sensible heat cospectra. Significant evaporation rates occurred during the winter months at this site. The wet canopy acted as a sink for energy characterized by downward fluxes of sensible heat supporting evaporation of intercepted rainfall. Latent heat fluxes often exceeded available energy and equilibrium evaporation rates on a half hour basis throughout the day and night. Wet canopy evaporation required turbulent conditions and only a small non-zero saturation deficit. Evaporation occurring between April and September, inclusively, accounted for 74% of the total annual evaporation of 402 mm for 1998. Summer evaporation rates were on average 1.57 mm day⁻¹ with a maximum of 3.56 mm day⁻¹. Sensible heat flux dominated energy exchange throughout the summer with β values ranging from 1.3 to 3.5. Uncorrected midday Priestly-Taylor α values ranged from 0.20 to 0.55. Physiological control was important in limiting dry canopy evaporation or transpiration rates. Mean daytime canopy conductance was generally less than 6 mm s⁻¹ and was closely related to saturation deficit, soil water potential, and photosynthetic photon flux density. However, canopy conductance was found to have a weak negative linear relationship with transpiration rates only during late morning hours.
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Comment cette classification a été obtenuedéplier
Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,000 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule tête enseignante, pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».