The impacts of climate change on ecosystem productivity and water resources over a long term in China are not well quantified. Precipitation-use efficiency (PUE) is a key parameter that describes carbon and water exchange in terrestrial ecosystems. Research on the response of regional PUE to climate change and its driving forces is of great significance to climate-change mitigation and the sustainable development of regional ecology. Based on an improved actual evapotranspiration (ET_a) model, the responses of ET_a, net primary productivity (NPP), and PUE to climate change in different climatic regions of China were analyzed; the contributions of various environmental factors to PUE changes were quantified; and the conversion characteristics and regulatory mechanisms of the PUE regime in different climatic regions were identified. The results indicate that the improved ET_a model, after considering the limiting effect of energy on ET_a in humid regions, can simulate the ET_a distribution in China well. Over the past 58 years (1960–2017), ET_a and NPP have increased in the western regions and decreased in the eastern regions, with the boundary at 103° E. PUE presents a “low-high-low” spatial distribution from northwest to southeast in China. It is noteworthy that there was a zonal distribution for a high value area of PUE, which coincided with the summer monsoon transition zone. The soil moisture (SM) increase in arid regions is the main driving force of the PUE increase, whereas the annual net radiation (Rn) change in humid regions is the main driving force of the PUE change. The transition zone is the conversion zone, where the prevailing factor limiting vegetation growth transitions from water to energy.

The interaction between soil moisture (SM) and evaporative fraction (EF), which reflects the degree of exchange of water and energy between the land and the atmosphere, is an important component of the theory of land–atmosphere coupling. Exploring the relationship between SM and EF in the transitional climate zone of China can help deepen our understanding of the characteristics of water and energy exchange in this region of strong land–atmosphere coupling. Data on observations in fluxes in the transitional climate zone revealed that fluxes in the energy on the surface of the land in this region exhibited significant inter-annual variations. The sensible heat flux (SH) exhibited the largest fluctuations in July and August, while the latent heat flux (LE) varied the most from June to August. The EF was found to exhibit weak correlations with indicators of vegetation growth such as the leaf area index, Normalized Difference Vegetation Index, and gross primary productivity in the transitional zone of the East Asian summer monsoon. By contrast, the relationship of land–atmosphere coupling between EF and SM in the transitional climate zone was stronger. Based on an analysis of the consistency of the relationship of SM-EF coupling, when the SMP reached 35%, there was a significant transition in the linear relationship between the SMP and EF that was consistent between the shallower and deeper layers of soil (0–40 and 40–80 cm). However, neither level had SM that reached saturation during the six-year observational period (2007–2012), and the mean values of its probability density function showed that the deep soil was drier than the shallow soil. This characteristic shows that SM plays a dominant role in variations in the EF in the transitional climate zone, which in turn indicates that constraints on the moisture govern the SM–EF relationship. The results of this study provide a better understanding of the mechanisms of land–atmosphere coupling in the transitional climate zone of China.

Land use/land cover (LULC) is a vital indicator reflecting the complex interactions between human society and terrestrial ecosystems. Investigating its spatiotemporal dynamics is fundamental for un...