Impact of climate, rising atmospheric carbon dioxide, and other environmental factors on water-use efficiency at multiple land cover types.

Rising atmospheric CO, changing climate, and other environmental factors such as nitrogen deposition and aerosol concentration influence carbon and water fluxes significantly. Water-use efficiency (WUE) was used to analyze these factors over 3 decades (1981-2010) using the Community Land Model 5.0 (CLM5.0). The study analyzes the effects of climate and other environmental factors on multiple land cover types (forest, grassland, and cropland) with divided study periods (1981-2000 and 2001-2010). Ecosystem WUE (EWUE) and transpiration WUE (TWUE) increased at the forest site due to the CO fertilization effect but decreased at the grassland and cropland sites due to lower gross primary production and higher/lower (cropland/grassland) evapotranspiration as consequences of rising temperature and water availability. Inherent WUE confirmed that EWUE and TWUE trends were controlled by the rising temperature and CO-induced warming through an increase in vapor pressure deficit. In this way, forest and cropland sites showed warming patterns, while the grassland site showed a drier climate. The later period (2001-2010) showed steeper trends in WUE compared with the earlier period at all sites, implying a change in climate. The results showed implications for rising temperature due to increased CO concentration at multiple land cover types.