Radiative characteristics in a Japanese forested drainage basin during snowmelt

Abstract

Abstract:Radiative characteristics in a forested drainage basin during the snowmelt season were examined in order to better understand and predict snowmelt runo in the basin. A method for estimating net radiation in a forest (R nf ) was presented using the total sky view factor (P) and the sun path sky view factor (Q). Solar radiation, albedo, atmospheric radiation and air temperature observed at an open site were also required. The total and the sun path sky view factors were determined from all-sky photographs. Q was expressed as a linear function of P for 0 . 15 5 P 5 0 . 86 regardless of forest type. For P 5 0 . 15, Q was set to zero, and for P 4 0 . 86, Q was equal to unity. The short-wave radiation budget at the forest¯oor (S nf ) increased with P, whereas the long-wave radiation budget (L nf ) decreased with P. R nf increased with P for 0 . 15 5 P 5 0 . 86, and changed little with P for P 5 0 . 15 and P 4 0 . 86, as the increase in S nf was oset by the decrease in L nf . The forest eect on R nf was diminished under cloudy or high albedo conditions, because S nf was easily oset by L nf . This estimation method was extended to the whole basin, and R nf was obtained over a watershed covered by trees. At the beginning of the snowmelt season when the albedo remained high, the forest eect became null because the decrease in S nf was balanced by the increase in L nf . As the albedo gradually lowered with the advance of the snowmelt season, the decrease in S nf owing to forest covers exceeded the increase in L nf , and the forest eect to decrease R nf became evident.

The impact of forest clear-cutting on soil temperature: a comparison between before and after cutting, and between clear-cut and control sites

“…This is probably because downward long-wave radiation (L Ø ) had a greater effect in the cool season. Generally, downward long-wave radiation (L Ø ) in forests is larger than that at open sites (Male and Granger 1981;Nakabayashi et al 1999). The difference in downward long-wave radiation is larger on clear days and smaller on cloudy days.…”

“…L Ø , L π , H, and ιE are written as follows (see, e.g., Male and Granger 1981;Kondo and Watanabe 1992;Tamai et al 1998;Nakabayashi et al 1999):…”