A review of the advances in water source composition and observation methods of evapotranspiration

Evapotranspiration is the link of water and energy transfer in the continuum of groundwater, surface water, soil, plants and the atmosphere (GSSPAC). Evapotranspiration is also a key in the study of land surface water balance. Affected by meteorological conditions, geological landforms, hydrogeological conditions and human activities, the mechanism of evapotranspiration process is complex, and its temporal and spatial variability is quite large. Based on many published journal papers, this paper comprehensively analyzes water resources and observation methods for evapotranspiration proposed by scholars at home and abroad. The results show that (1) surface water (rivers, lakes, etc.), soil water, groundwater and vegetation intercepted water are the major water sources of evapotranspiration. (2) The methods for measuring evapotranspiration can be divided into hydrology method, plant physiology method, micro-meteorological method and isotope method. These methods have advantages in studying the process and driving mechanism of evapotranspiration. (3) Different evapotranspiration measurement methods are suitable for different spatiotemporal scales, and more reliable evapotranspiration data can be obtained by integrating various measurement methods. According to the current situation of evapotranspiration researches, the next step is to strengthen the coupling mechanism researches of water transport in the GSSPAC system, and strengthen interdisciplinary researches to further clarify the interaction mechanism of water, energy and material cycle and flow. In addition, through the construction of monitoring network on different climate and geomorphic units, we can gain basic data of evapotranspiration variation under the interaction of multiple influencing factors, which can support large-scale and refined evapotranspiration researches.