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Radiative characteristics in a Japanese forested drainage basin during snowmelt
Author(s) -
Nakabayashi H.,
Ishikawa N.,
Kodama Y.
Publication year - 1999
Publication title -
hydrological processes
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.222
H-Index - 161
eISSN - 1099-1085
pISSN - 0885-6087
DOI - 10.1002/(sici)1099-1085(19990215)13:2<157::aid-hyp704>3.0.co;2-f
Subject(s) - snowmelt , albedo (alchemy) , sky , radiative transfer , atmospheric sciences , environmental science , surface runoff , watershed , structural basin , hydrology (agriculture) , snow , meteorology , geology , physics , geomorphology , ecology , art , geotechnical engineering , quantum mechanics , machine learning , performance art , computer science , biology , art history
Radiative characteristics in a forested drainage basin during the snowmelt season were examined in order to better understand and predict snowmelt runoff 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< P <0·86 regardless of forest type. For P <0·15, Q was set to zero, and for P >0·86, Q was equal to unity. The short‐wave radiation budget at the forest floor ( S nf ) increased with P , whereas the long‐wave radiation budget ( L nf ) decreased with P . R nf increased with P for 0·15< P <0·86, and changed little with P for P <0·15 and P >0·86, as the increase in S nf was offset by the decrease in L nf . The forest effect on R nf was diminished under cloudy or high albedo conditions, because S nf was easily offset 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 effect 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 effect to decrease R nf became evident. Copyright © 1999 John Wiley & Sons, Ltd.