PNNL

Abstract

Sediment yield (SY) plays an important role in the global carbon cycle for carrying particulate carbon into rivers and oceans, but it is rarely represented in Earth System Models (ESMs). Existing SY models have mostly been tested over a few small catchments in specific regions or in large river basins globally. By comparing the performance of eight well-known SY models in over 450 small catchments across the United States, Canada, Puerto Rico, U.S. Virgin Islands and Guam, we identified the simple Morgan model for its better performance in representing the spatial variability of regional scale SY at spatial scales relevant to ESMs than other models because of a more realistic representation of runoff-driven erosion and sediment transport capacity. The results also indicated that runoff-driven erosion should be formulated using an exponential function of runoff, shear stress or stream power to better represent the total effect of concentrated flow if gully erosion and channel erosion are not explicitly modeled. We also demonstrated that the Morgan model can be further improved by removing snowmelt-driven runoff in the calculation of runoff-driven erosion and integrating with a landslide model. The improved Morgan model explains 52% of the spatial variability of the measured mean annual SY. The new model also demonstrated the capability to simulate fine temporal-scale SY in cross-validation catchments, which is important for studying river biogeochemistry and the global carbon cycle using ESMs.