Suppression of spring rain by surface greening over North China Plain

Surface greenness and rainfall in spring have changed from the 1980s to 1990s over the North China Plain (NCP). The greenness changes are characterized by large increase in north and little in south with an obvious greening zone from the centre of the NCP to the northeast. The rainfall change has a similar spatial pattern with reversed sign. The correlation between changes in greenness and rainfall is significant and the correlation (r=-0.71, p<0.001) is highest for light rainfall. The number of light rainfall days decreased by only approximate to 10% at the stations where the Normalized Differences Vegetation Index (NDVI) did not change, whereas it decreased by up to approximate to 30% at the stations where NDVI increased by 20%. Further analyses found that surface greening increased evaporation wetting the atmosphere and, meanwhile, reduced sensible heat flux to cooling surface air. The cooling surface promotes the air stability and thus suppresses the occurrence of rainfall. This finding supports that surface cooling effects from greening play a more dominant role on occurrence of spring rainfall than the wetting effect in the NCP.