Background/Question/Methods Background: The consistent increase in forest Water use efficiency is considered as the most reliable and prompt strategy to deal with with higher atmospheric CO2 concentration in the atmosphere, which would tend to counter the tendency to apply extra water as temperature increases. Forests absorb CO2 from the atmosphere for photosynthesis and grow at the cost of water losses due to transpiration from stomata on the leaves ultimately enhance their growth and productivity. The magnitude of the trends in WUEgpp and underlying processes varies greatly in different forest types on global and regional scales. However, the exact estimation of these annual trends in WUEgpp of different forest types on a global scale study is largely lacking. Moreover, the influence of annual temperature and precipitation on annual WUEgpp of forest ecosystem are the important features to better apprehend the complexity of future climatic change issues. Question: To determine the global patterns of variability in the forest ecosystem WUEgpp, and their underlying controls. Methods: Data for annual WUEgpp was synthesize from 156 forest sites using using eddy covariance and Modeling techniques from all over the world Results/Conclusions Our analyses revealed a greater increase in WUEgpp of mixed(MX) forest stands followed by broadleaved(BL) than needle-leaved (NL) forests (p<0.0001). Similarly, WUEgpp of deciduous (DEC) forest is significantly higher than Evergreen (EV) forests across the globe (p<0.0001). Annual temperature is showing increasing trend in WUEgpp of MX and NL and declining the BL forest stand. Similarly, DEC forests showing decline in WUEgpp whereas EVE showed no significant trend. Annual precipitation influencing negatively on WUEgpp of BL, while in case of NL and MX this trend is positive. The decreased stomatal conductance might be contributing in the upsurge in WUEgpp of BL, whereas the increased gross primary productivity acted as the main cause for the rise in WUEgpp of NL and MX forests. The decline in WUEgpp of deciduous forests indicating that future climate extremes might impacted these stands drastically. Therefore, during future planning of afforestation projects the selection of most suitable species will be taken into account, which will better to compete the challenges of climate change along with efficient water utilization for attaining growth and productivity.