Warming/cooling effects of cropland greenness changes during 1982-2006 in the North China Plain
This study analysed the changes in cropland greenness during 1982-2006 in the North China Plain (NCP) and investigated the warming/cooling effects of the greenness changes. The results show that while spring cropland greenness increased, early summer cropland greenness substantially decreased from 1982 to 2006. In contrast to the cooling and wetting effects of the greenness increase in spring, the greenness reduction in early summer had warming and drying effects. The cooling/warming effects of cropland greenness changes accounted for similar to 47% of the spatial variance of daily maximum temperature (T-max) change in spring and similar to 44% in early summer. The wetting/drying effects of cropland greenness changes accounted for similar to 48% of the spatial variance of daily minimum specific humidity (SPHmin) change in spring and similar to 19% in early summer. The cooling-wetting/warming-drying effects mainly resulted from the distinct partitioning of surface net radiation between surface latent heat flux and sensible heat flux over cropland with different greenness. Canopy transpiration plays a dominant role. The increased (decreased) cropland greenness corresponds to high (low) transpiration rate, less (more) sensible heat flux and high (low) humidity, and consequently cooling-wetting (warming-drying) effects. In comparison, there was little change in surface net radiation, although surface albedo and emissivity had changed with greenness change.