3.1.1. Sensitivity of annual forest GPP
On average, decreasing ASWC to 50 mm from 200 mm had only a moderate influence (5–20% change) on annual forest GPP estimates within all level 1 ecoregions across the U.S.A. (Fig. 1a). Ecoregions containing forests that showed > 20% variation in GPP with a large reduction in ASWC were predominately in the south, central and western parts of the country and included: 6 (Northwestern forested mountains); 9 (Great Plains); 10 (North American Deserts); 11 (Mediterranean California); and 13 (Temperate Sierras) (Fig. 1 and Fig. 2). Ecoregions with a large proportion of forested pixels showing < 5% variation in GPP values from the standard ASWC of 200 mm included: 9 (Great Plains), 13 (Temperate Sierras) and 15 (Tropical Wet Forests) (Fig. 1a).