Personne : Nadeau, Daniel
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Nadeau
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Daniel
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Université Laval. Département de génie civil et de génie des eaux
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ncf11887096
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- PublicationAccès libreApplicability of the bulk-transfer approach to estimate evapotranspiration from boreal peatlands(American Meteorological Society, 2015-07-29) Isabelle, Pierre-Erik; Nadeau, Daniel; Coursolle, Carole.; Rousseau, Alain N.; Margolis, Hank A.In northern landscapes, peatlands are widespread and their hydrological processes are complex. Furthermore, they are typically remote, limiting the amount and accuracy of in situ measurements. This is especially the case for evapotranspiration ET, which strongly influences watershed hydrology. The objective of this paper is to demonstrate the validity of the bulk-transfer approach to estimate ET over boreal peatlands. The simplicity of the model relies on four assumptions: (i) near-neutral atmospheric conditions; (ii) wet surface; (iii) constant momentum roughness length depending on vegetation height; and (iv) constant water vapor roughness length, with the last two assumptions implying a constant water vapor transfer coefficient CE. Using eddy covariance data from three Canadian peatlands—Necopastic (James Bay, Québec), Mer Bleue (Ottawa, Ontario), and Western Peatland (Athabasca, Alberta)—this paper shows that these sites are characterized by frequent occurrences of near-neutral atmospheric conditions, especially the Necopastic site, with nearly 76% of the 30-min data segments occurring under near-neutral stratification. The analysis suggests these near-neutral conditions occur as a result of strong mechanical turbulence and weak buoyancy effects. The bulk-transfer approach gives promising results for 30-min and daily ET in terms of mean error and correlation, with performances similar to the Penman equation, without requiring net radiation data. The accuracy of the approach is likely related to the number of near-neutral periods and the elevated position of the water table, which backs up the wet surface assumption.
- PublicationAccès libreImpacts of high precipitation on the energy and water budgets of a humid boreal forest(Elsevier, 2019-10-24) Isabelle, Pierre-Erik; Anctil, François; Nadeau, Daniel; Rousseau, Alain N.; Music, Biljana; Jutras, SylvainThe boreal forest will be strongly affected by climate change and in turn, these vast ecosystems may significantly impact global climatology and hydrology due to their exchanges of carbon and water with the atmosphere. It is now crucial to understand the intricate relationships between precipitation and evapotranspiration in these environments, particularly in less-studied locations characterized by a cold and humid climate. This study presents state-of-the-art measurements of energy and water budgets components over three years (2016–2018) at the Montmorency Forest, Québec, Canada: a balsam fir boreal forest that receives ∼1600 mm of precipitation annually (continental subarctic climate; Köppen classification subtype Dfc). Precipitation, evapotranspiration and potential evapotranspiration at the site are compared with observations from thirteen experimental sites around the world. These intercomparison sites (89 study-years) encompass various types of climate and vegetation (black spruces, jack pines, etc.) encountered in boreal forests worldwide. The Montmorency Forest stands out by receiving the largest amount of precipitation. Across all sites, water availability seems to be the principal evapotranspiration constraint, as precipitation tends to be more influential than potential evapotranspiration and other factors. This leads to the Montmorency Forest generating the largest amount of evapotranspiration, on average ∼550 mm y−1. This value appears to be an ecosystem maximum for evapotranspiration, which may be explained either by a physiological limit or a limited energy availability due to the presence of cloud cover. The Montmorency Forest water budget evacuates the precipitation excess mostly by watershed discharges, at an average rate of ∼1050 mm y−1, with peaks during the spring freshet. This behaviour, typical of mountainous headwater basins, necessarily influence downstream hydrological regimes to a large extent. This study provides a much needed insight in the hydrological regimes of a humid boreal-forested mountainous watershed, a type of basin rarely studied with precise energy and water budgets before.
- PublicationRestreintEstimating sensible and latent heat fluxes over an inland water body using optical and microwave scintillometers(Springer, 2022-09-15) Pierre, Adrien; Isabelle, Pierre-Erik; Nadeau, Daniel; Thiboult, Antoine; Perelet, Alexei; Rousseau, Alain N.; Anctil, François; Deschamps, JarilLes flux de chaleurs turbulents sont encore trop rarement observés au-dessus des plans d’eau continentaux comme les lacs ou les réservoirs, alors que cela demeure essentiel pour le paramétrage des modèles de prévisions météorologiques et de projections climatiques. La scintillométrie permet d’estimer à l’échelle régionale (~km2) les flux turbulents, mais peu d’études ont évalué sa performance au-dessus de plans d’eau. Cette étude compare les flux de chaleurs turbulents issus de la méthode de scintillométrie avec ceux issus d’un système de covariance des tourbillons installé sur un quai flottant, au-dessus d’un réservoir hydroélectrique boréal, dimictique, de 85 km2, situé dans l’est du Canada (50.59°N, 63.24°O). À notre connaissance, il s'agit de l'une des premières études à quantifier l'évaporation sur un plan d'eau intérieur à l'aide d'un ensemble de scintillomètres optiques et micro-ondes. Du 14 août au 9 octobre 2019, les faisceaux des scintillomètres ont sondé l’atmosphère sur une distance de 1.7 km au-dessus du réservoir (10 m) dans une zone ayant jusqu’à 100 m de profondeur. Quarante-neuf jours de données ont été récoltés. Cette étude quantifie l'impact de la stabilité atmosphérique sur les flux calculés et explore l'utilisation des différences de température à l'interface eau-air à proximité du centre du faisceau du scintillomètre pour estimer correctement la direction du flux de chaleur sensible. Les méthodes de scintillométrie corrèlent bien avec les estimations de la covariance des tourbillons pour les flux de chaleur sensible (R2 jusqu'à 0.86, 43% de biais), tandis que la concordance diminue pour les flux de chaleur latente (R2 jusqu'à 0,58, 70% de biais). Le scintillomètre a mesuré des flux de chaleur latente beaucoup plus importants que le système de covariance des tourbillons. Ces résultats peuvent être dus à l'empreinte plus grande des scintillomètres qui captent une plus grande hétérogénéité des flux.