Trend and impact factors of evaporation from shallow phreatic groundwater of bare soil on Huaibei Plain in China

To reveal the law and mechanism of the bare soil evaporation on Huaibei Plain, using observation data from hydrological station of Wudaogou in the area of Huaibei from 1991 to 2008. The paper analyzed the monthly distribution of evaporation from the shallow phreatic groundwater in bare soil and the trend changing with soil texture and depth, determined the seasonal time series trend of evaporation from the shallow phreatic groundwater in bare soil of this region using the cumulative departure curve method combined with the Mann-Kendall method.The forces of phreatic evaporation was also explored by investigating several hydro-meteorological elements on the two kinds of soil texture and the depth of the impact using statistical software SPSS. The results showed that the ratio of evaporation between fluvo-aquic soil and lime concretion black soil expanded with the increase of phreatic depth. The evaporation quantity of bare soil on Huaibei Plain over the years increased in Spring giving the greatest contribution; however, it did not meet the “evaporation paradox”. For the lime concretion black soil depth at 0.4 m to shallow and fluvo-aquic soil at 1.0 m to shallow, it showed a significant correlation between phreatic groundwater evaporation and main meteorological factors. This indicated that the transfer process of geothermal heat in the vertical direction coincided with the evaporation distribution of the year. The results of the current study will be greatly beneficial to grasp the evaporation rules accurately and understand the hydrologic cycle better.