Here, the year 2011 characteristics of evapotranspiration and the energy budget of a black spruce forest underlain by permafrost in interior Alaska were explored. Energy balance was nearly closed during summer, and the mean value of the daily energy balance ratio (the ratio of turbulent energy fluxes to available energy) from June to August was 1.00, though a large energy balance deficit was observed in the spring. Such a deficit was explained partly by the energy consumed by snowmelt. Ground heat flux played an important role in the energy balance, explaining 26.5% of net radiation during summer. The mean daily evapotranspiration of this forest during summer was 1.37 mm day^<−1> - considered typical for boreal forests. The annual evapotranspiration and sublimation yielded 207.3 mm year^<−1>, a value much smaller than the annual precipitation. Sublimation accounted for 8.8% (18.2 mm year^<−1>) of the annual evapotranspiration and sublimation; thus, the sublimation is not negligible in the annual water balance in boreal forests. The daytime average decoupling coefficient was very small, and the mean value was 0.05 during summer. Thus, evapotranspiration from this forest was mostly explained by the component from the dryness of the air, resulting from the aerodynamically rough surface of this forest.
内容記述
アラスカ内陸の永久凍土上に成立するクロトウヒ林を対象に、2011年に通年で熱収支観測を実施した。6月から8月までの夏期には熱収支がほぼ閉じ、地中熱流量が正味放射量の26.5％を占めた。一方、熱収支の残差は春に大きかったが、積雪調査日から消雪日までの熱収支の残差は、実測した積雪水量の融解に消費される潜熱でほぼ説明された。夏期の平均日蒸発散量は1.37 mm day^<-1> で、年間の水蒸気輸送量は207.3 mm year^<-1> であった。そのうち昇華量は全体の8.8％ (18.2 mm year^<-1> ) と見積もられ、年間水収支で無視できないことが分かった。夏期のdecoupling係数は0.05と非常に小さく、蒸発散のほとんどが大気側の寄与で説明された。
Characteristics of evapotranspiration from a permafrost black spruce forest in interior Alaska
概要
