The author simulated water/heat dynamics in the North China plain (NCP) by coupling the NIES Integrated Catchment-based Eco-hydrology (NICE) model series with dam/canal systems in the agricultural and urban areas (NICE-CNL). This combined model was applied to the Hai River catchment and the lower reach of the Yellow River (530 km wide x 840 km long) at a resolution of 5 km. It satisfactorily reproduced river discharge, soil moisture, evapotranspiration, groundwater level, and crop production of summer maize and winter wheat, correctly estimating-without any detailed statistical data-the amount of crop water use. The simulation showed that irrigation and industrial use of groundwater has a marked effect on the water dynamics in the NCP because the river water volume is smaller than that necessary for irrigation, industrial and, domestic water use. The model reproduced, reasonably well, the trend of groundwater degradation over the previous half century, including cone depressions occurring around bigger cities, which the author was unable to reproduce in previous research. The simulation also clarified that this water shortage is related to the low flow discharge of the Hai River into the ocean. Furthermore, the simulated result for the density current and solute transport processes clarified that these water cycle changes have caused serious seawater intrusion and a decrease of crop productivity in the coastal area, as shown by the gradient of NDVI (Normalized Difference Vegetation Index) estimated from satellite images. This study has important implications for the evaluation of ecosystems and environments located on the moving edge of freshwater and marine areas. Copyright (C) 2011 John Wiley & Sons, Ltd.