Divergent negative spring vegetation and summer runoff patterns and their driving mechanisms in natural ecosystems of northern latitudes

摘要

The reported wide change in natural vegetation growth in the Northern Hemisphere could have altered hydrological cycles in the past 30 years. However, it is hard to understand the underlying mechanisms for substantial variations in the magnitude and direction of runoff response to vegetation change. Models fail to clearly identify the underlying mechanisms due to limitations in accommodating all the driving factors of the extremely complex reality. This study used a data-driven approach to determine the linkages between Normalized Difference Vegetation Index (NDVI) and runoff in the spring and summer seasons of 1982-2015 in 3600 + northern mid/high-latitude (>= 30 degrees N) catchments. The results suggested that a significant (p < 0.05) negative correlation existed between spring NDVI and summer runoff in the Rocky Mountains, the Great Lakes region, the northern Scandinavia and the Alps. 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. Both anthropogenic warming and Arctic amplification might influence the patterns of vegetation-runoff in the region. Our findings can help improving the understanding on how vegetation change affects runoff and enhancing the forecasting abilities of hydrological models.