The significant impact of earlier leaf-out on hydrological circulation over the North Hemisphere

My first year Postdoc project was developing a novel approach coupling remote sensing big data techniques to uncover the impact of advanced leaf-out on hydrology. Although widely advanced leaf-out has been unambigously reported over north hemisphere, much of focus remains largely on the impact on the carbon balance with few on the hydrological cycle. Evapotranspiration (ET) is one of the most important component in hydrological circle, directly effects on precipitation and soil moisture, rivers and lakes. Therefore, We explored the impact of earlier leaf-out on hydrological circulation over the North Hemisphere: a case study on ET. Our results show advanced leaf-out mainly effect on spring Etvariation, accounting for 29%, yet only 2% in summer. Besides, the advanced leaf-out contribution of -0.282 mm day-1 to the ET changes along 3-days sos gradient in spring future indicates its key role on hydrology, which also varing with vegetation species (Fig 1 and Fig 2).  

Fig 1. Maps of 3-days sos gradient based on the sos change between years 1982-1991 and years 2002-2011 (a) and of land cover (b). Land cover map was extracted from Classification system of International Geosphere-Biosphere Programme (IGBP) of MCD12Q1 in 2010 year with 500 m resolution and then resampled to 0.5° using nearest neighbour method.

Fig 2. sos-related individual contribution patterns of sos to ET along 3-day sos gradients in spring. Only the sos intervals contained more than 20 pixels were used to build the linear regression along sos gradient. The unite of the linear slope is mm day-1. The corresponding function is printed at the right corner with goodness of fit (r). The following triple asterisk in right chart represented that the trend was significant with p value of F-test less than 0.001, double asterisk and one asterisk meant p value is less than 0.01 and 0.05, the other was p value more than 0.1. Box heights correspond to the interquartile range, whiskers span up to 1.5 times the interquartile range, and the horizontal line corresponds to the median. The number at the top represents number of pixel at each sos group.


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