Study On Water Surface Evaporation And Its Influencing Factors In Guanzhong Basin

Guanzhong Basin is located in the central part of Shaanxi Province with less rainfall,strong evaporation and relatively scarce water resources.However,with population growth and rapid economic development,large-scale use of water resources and large-scale water pollution have resulted in contradictions between water supply and demand.Increasingly sharp,it has become a bottleneck restricting the sustainable development of Guanzhong Basin.In addition,water evaporation is an important part of the accurate calculation of water resources.Therefore,the study of the mechanism of water surface evaporation,accurate evaluation of evaporation and it's influencing factors in this area is an urgent task to be solved.This paper takes Guanzhong Basin as the research area and obtains the vertical temperature distribution in water bodies and evaporation data of different areas and depths through in-situ observation experiments.Combined these data with meteorological data,we discuss the characteristics of heat transfer and evaporative flux in different water bodies(different areas and different depths)and analyzes the influence of meteorological factors on water surface evaporation.On the basis,we study the quantitative relationship between the water area(water depth)and evaporation.And,we compare the applicability of the widely used water surface evaporation models in the study area.The main conclusions are as follows:(1)On the hourly scale,the lowest temperature above the surface of the water appears at 2 a.m.,the highest temperature occurs at 13 o'clock or 14 o'clock;the lowest water temperature in the water body occurs between 5 am and 7 a.m,the highest water temperature occurs from 15 o'clock to 16 o'clock,all the above are consistent with the intraday variation of solar radiation.The water surface temperature lags behind the temperature by about 2 hours.As the depth of water increases,the lag time becomes longer and longer.On the monthly scale,the maximum temperature appears in July or August,the minimum temperature occurred in January,which is in line with the annual change in solar radiation.(2)The difference between the maximum and minimum temperature shows a pattern: in the water body <in the water surface < above the water surface.The evaporation at the surfaceof the water changes the temperature of its surrounding environment.For different areas of water,the larger the area of water,the greater its ability to improve the temperature above the water surface,but the effect of water area on the temperature change in the water body is not obvious.For different depths of water,the water depth is inversely proportional to the temperature change in the water within a day,but the depth change has no obvious effect on the air temperature above the water surface.To change the air temperature above the water surface,the area of the water must be changed;in order to change the temperature in the water body,the depth of water must be changed.(3)In the Guanzhong basin,the ‘area effect' between evaporation and water surface area was studied.It was found that evaporation was inversely proportional to the area of water body,and the relationship between evaporation and evaporation area was obtained as follows:(?)Further analysis shows that when the surface area is larger than 32m2,the evaporation rate does not increase with the area.The 'depth effect' between evaporation and depth of water bodies was studied.It was found that evaporation was inversely proportional to the depth of the water bodies,and the relationship between the evaporation and depth was as follows:(?)From this equation,we can found that after the water depth exceeds 4 meters,the evaporation rate does not increase with the increase of water depth.(4)Through path analysis,the effects of surface temperature,air temperature,solar radiation,relative humidity and wind speed on evaporation have been studied.The degree of impact was ranked from highest to lowest: water surface temperature> solar radiation> wind speed > relative humidity> air temperature.The correlation coefficient between water surface temperature and evaporation is the highest(0.733),followed by solar radiation(0.725).The direct path coefficients of water surface temperature and solar radiation to evaporation are 0.416 and 0.390,which are the highest among all impacts.The water surface temperature contribution to R2 is 0.305,the path coefficient is 0.1733;the contribution of solar radiation toR2 is 0.283,the path coefficient is 0.1517;the contribution of two-factor surface temperature and solar radiation to R2 is 0.1128.The above shows that in the evaporation process on the water surface,the water surface temperature and solar radiation have the strongest effect.(5)On the tenth scale,through comparison and analysis of different evaporation models,it is considered that the mass transfer model has a simple structure,fewer parameters and an optimal prediction performance;the modified de-Bruin model has excellent accuracy and fidelity;the neural network models(BP and GRNN)also perform well.They are recommended to use in the Guanzhong basin area for the evaluation of water surface evaporation.