Climate and land use have been suggested as two major factors that control variations of water yield and soil moisture in the world. Landscapes of the North America (NA) have been intensively disturbed or managed by human activities and have been involved in rapid economic development and urbanization in the last century. A number of previous studies through long-term hydrological observations have investigated the effects of land-use change, forestry management, and natural disturbances on the dynamics of water yield, sediment load, peak stream flow, and water table on watershed levels.  Long-term, widely distributed gauge observation system in NA provided plentiful data on characterizing the monthly or daily hydrographs for large rivers. However, few integrated regional studies had been conducted to characterize how climate variations and climate change, land-use conversions, and land management have affected regional hydrological cycles and soil moistures in temporal and spatially domain and further attribute these changes in hydrological variables to each individual factor and their interactions.

In this study, we used the improved Dynamic Land Ecosystem Model (DLEM) in multiple soil layers, simplified groundwater model, river routine and water transporting system, and cohort structure to estimate how transient land- use conversions, climate change, and land management affect the major hydrological variables including evapotranspiration, surface runoff, subsurface runoff, water table levels, and soil moisture profiles across the NA continent over the last thirty years.

Results/Conclusions Our study shows that the integrated terrestrial model can estimate the combining effect of climate change and humans activities on hydrological processes and identify the relative contribution from each factor. The simulation results indicate that the inter-annual variation of river discharge is primarily controlled by climate change, especially the precipitation. Land-use change, one the contrary, shows relatively less contributions on the variations of river discharge the NA as a whole. However, the effects of land use change and management on river discharge show large spatial variation and long-term effects through changing ET and the patterns of seasonal soil moisture profiles. The simulation results are qualitatively consistent with gauge observations, paired watershed experiments, and long-term mean river discharge map.