ESTIMATION OF SURFACE NET-RADIATION IN THE BOREAL FOREST AND NORTHERNPRAIRIE FROM SHORTWAVE FLUX MEASUREMENTS

The relationships between net radiation and surface shortwave fluxes w ere explored by using one year of 15 min surface flux data for nine si tes in central Canada. The sites were located throughout a 50,000 km(2 ) area, in conjunction with the BOREAS project, across a gradient in s urface cover from prairie grassland to boreal forest. When insolation alone was used to estimate instantaneous net radiation, the r(2) value s at the nine sites ranged from 0.93 to 0.98. The use of the net short wave flux as a predictor improved the range in r(2) values to between 0.96 and 0.99. The root-mean-square error across sites varied from 26 to 41 W m(-2) without albedo to a range of 18-36 W m(-2) when albedo w as included. The data for all sites were combined to produce a single linear relationship with an r(2) value of 0.97 and a root-mean-square error (RMSE) of 29 W m(-2) when the surface albedo is included. Cross validations were performed where the data for eight sites were used to predict net radiation at a ninth (excluded) site, revealing little si te-specific bias. Classifications of the data by season and by transmi ttance provided little improvement in estimated net radiation at any s ite. Our study suggests that a single equation using net shortwave flu x alone can be used to estimate net radiation for large portions of th e boreal forest and northern prairie, regardless of spatial and tempor al variation in surface cover and atmospheric conditions.