Global vegetation coverage has significantly increased over globe since 1980s, which is called "Earth's greening". A major concern about the vegetation change is how it impacts runoff. To date, there still lacks consensus. A study conducted by scientists from Chinese Academy of Sciences reveals four patterns of vegetation-runoff relationships and their mechanisms, which has been published in Journal of Hydrology.  

There are three limitations in most previous studies: (i) the failure to distinguish Earth's greening induced by human activities from climate change; (ii) the over generalization of using one mechanism to explain substantial variation, e.g., LAI, CO₂ concentration, and photosynthesis; (iii) the over emphasis on evapotranspiration rather than other factors, e.g., precipitation, and soil moisture. Therefore, using data-driven method, the study analyzed the relationships between spring NDVI and spring/summer runoff in the period of 1982-2015 over 3670 natural catchments in Northern Hemisphere. Results showed significantly negative relationships between spring NDVI and summer runoff in the Rocky Mountains, the Great Lakes Region, the Alps and the northern Scandinavia. Four patterns were further summed up from the relationships and their mechanisms were given. In the southern Rocky Mountains, there was a significant increase in spring NDVI and a decrease in summer runoff due to loss of snowpack. In the Great Lakes region, significant decrease in spring NDVI was accompanied by increase in summer runoff. Earlier spring onset and consequent withering vegetation in late spring significantly reduced spring NDVI while slightly increased summer runoff in Northern Rocky Mountain. The warmer and wetter winter could have increased spring NDVI owning to better water/energy environment, and insignificantly reduced summer runoff in northern Scandinavia and the Alps. 

For the first time, the study proposes that Arctic Amplification is one of key driving factors for vegetation-runoff relationships in some regions.

The study is supported by the National Natural Science Foundation of China (Grant No. 41971032) and the open fund provided by the Key Laboratory of Water Cycle and Related Land Surface Processes, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences (Grant No. WL2019004).