Climate over the Haihe River Basin in northern China has changed significantly over the past five decades. To improve understanding of climate change effects on the water cycle in this mountainous region, a team of scientists including a DOE researcher at Pacific Northwest National Laboratory, found that climate-induced runoff in this region has displayed a decreasing trend since 1960. Using version 4 of the Community Land Model (CLM4), they quantified the spatiotemporal changes in runoff across the region and attributed the changes to various climatic factors and the direct effects of increasing CO₂ concentration. The team found that changes in precipitation, solar radiation, air temperature, and wind speed accounted for 56%, 14%, 13%, and 5% of the overall decrease in annual runoff, respectively, although the relative contributions of those factors varied across the study area. They determined a rise in atmospheric CO₂ concentration had a limited effect on runoff through its impacts on plant water use efficiency and biomass growth. They found that a significant decrease in runoff in the southern and northeastern portions of the region could be primarily attributed to decreasing precipitation, whereas decreasing solar radiation and increasing air temperature were the primary causes of a slight runoff increase in the northern portion. The team’s findings suggest that the magnitude of the decreasing trend may be greatly underestimated if the dynamic interactions of vegetation phenology and the environmental factors are not considered in the modelling, thus indicating the importance of including vegetation dynamics in the long term prediction of runoff trends in this region.