The spatial and temporal characteristics of vegetation biophysical processes (VBP)/ atmospheric climate interactions are poorly understood. Most land/atmosphere interaction studies thus far focus on albedo and soil moisture with summer being the primary season. VBP directly affects the effect of land cover and land use (LCLU) change and terrestrial carbon exchange. A realistic and credential assessment of the role of land surface in climate system and the impact of LCLU change on climate for the societal planning require a comprehensive understanding of the VBP.

The present study provides a global and seasonal assessment of vegetation biophysical process (VBP) effects on the climate system. The method is based on general circulation models of the atmosphere (AGCM) coupled to land models that represent different land surface processes, including comprehensive VBP representation to partial or no VBP representation. The focus is on precipitation. The VBP effects are expressed by the change in biases and root-mean-square-errors (RMSE) of simulated fields from AGCM coupled with different land models in reference to observed climatology.

It is shown that accounting of VBP effects reduces the bias in annual precipitation over land by 62% (about 40% of the total precipitation over land) and RMSE by 42%. The strongest impacts are in monsoon regions, where the average reductions of bias and RMSE are more than 10% higher than the global average. The high latitude land region has least influence with about 40% of bias reduction. The impacts occur mainly in spring, summer, and fall with different regions having different primary impact season(s) depending on regional climate characteristics and geographical features. In a study investigating partial VBP effect, which excluding interactive soil moisture and vegetation albedo, the partial VBP effect reduces annual precipitation bias over land that equals to about 13% of total precipitation over land. It is also found that this partial VBP effect plays a great dominant role in the high latitude region, accounting about 80% of VBP effect. This is a first study intending to comprehensively quantitatively assess all relevant biophysical processes (not only soil moisture or surface albedo) and their global spatial (no limited to a few regions) and temporal (not limit to summer) characteristics. The results suggest a notion that VBP feedback is a major component of the global water cycle over land and must be comprehensively considered in climate change studies, especially for the future climate projection.