RUNOFF INDEX VALUES FOR FROZEN SOIL AREAS OF THE PACIFIC-NORTHWEST

Several operational hydrology and erosion models use the NRCS Runoff C urve Number procedure to estimate runoff. However, runoff Curve Number s are poorly defined and perhaps inappropriate for areas such as the P acific Northwest where the annual hydrology is dominated by winter pro cesses of snowfall and soil freezing and thawing. Hence, these models do not perform well under these conditions. This has hampered successf ul we of models such as EPIC, CREAMS, and AGNPS in the region. Runoff index values have been calculated wing runoff curve number relationshi ps from runoff plot data from the Palouse Conservation Field Station n ear Pullman, Washington. These runoff index values range considerably higher than Curve Numbers commonly wed in hydrologic planning and can be wed to improve performance of Curve Number based models under winte r conditions of the Pacific Northwest.