Effect of climate change on the trends of evaporation of phreatic water from bare soil in Huaibei Plain, China

When the soil condition and depth to water table stay constant, climate condition will then be the only determinant of evaporation intensity of phreatic water from bare soil. Based on a series of long-term quality-controlled data collected at the Wudaogou Hydrological Experiment Station in the Huaibei Plain, Anhui, China, the variation trends of the evaporation rate of phreatic water from bare soil were studied through the Mann-Kendall trend test and the linear regression trend test, followed by the study on the responses of evaporation to climate change. Results indicated that in the Huaibei Plain during 1991-2008, evaporation of phreatic water from bare soil tended to increase at a rate of 5% on monthly scale in March, June and July while in other months the increase was minor. On the seasonal basis, the evaporation saw significant increase in spring and summer. In addition, annual evaporation tended to grow evidently over time. When air temperature rises by 1 °C, the annual evaporation rate increases by 7.24–14.21%, while when the vapor pressure deficit rises by 10%, it changes from-0.09 to 5.40%. The study also provides references for further understanding of the trends and responses of regional evapotranspiration to climate change.

Soil-atmosphere interaction in earth structures

The soil-atmosphere interaction was investigated through laboratory testing,field monitoring and numerical monitoring.In the laboratory,the soil water evaporation mechanisms were studied using an environmental chamber equipped with a large number of sensors for controlling both the air parameters and soil parameters.Both sand and clay were considered.In case of sand,a dry layer could be formed during evaporation in the near surface zone where the suction corresponded to the residual volumetric water content.The evaporative surface was situated at a depth where the soil temperature was the lowest.In case of clay,soil cracking occurred,changing the evaporative surface from one-dimensional to three-dimensional nature.The suctionbased evaporation model was adapted to take these phenomena into account by adopting a function of dry layer evolution in the case of sand and by adopting a surface crack ratio and a retative humidity ratio in the case of clay.In the field,the volumetric water content,and the suction as well as the runoff were monitored for an embankment constructed with lime/cement treated soils.It appeared that using precipitation data only did not allow a correct description of the variations of volumetric water content and suction inside the soils,the consideration of water evaporation being essential.It was possible to use a correlation between precipiration and runoff.The hydraulic conductivity was found to be a key parameter controlling the variations of volumetric water content and suction.For the numerical modelling,a fully coupled thermohydraulic model was developed,allowing analyzing the changes in temperature,volumetric water content and suction of soil,with the upper boundary conditions at the interface between soil and atmosphere determined using meteorological data.Comparison between simulations and measurements showed the performance of such numerical approach.