| The evaporation rate is a key factor in calculating the water requirements of crops and forms the foundation for developing an irrigation system.Changes in regional evaporation rates can indicate variations in the local climate,making it crucial for crop growth and water resource management.In this paper,based on the daily evapotranspiration observation data from 63 meteorological stations in the Songhua River basin between 1961 and 2020,as well as meteorological factor data such as temperature,air pressure,sunshine hours,wind speed,and precipitation.The study used the Mann-Kendall abrupt change test,multiple regression analysis,cumulative anomaly,conducted an analysis of the spatiotemporal variations and influencing factors of annual and seasonal evapotranspiration in the Songhua River basin,utilizing methods such as climate tendency rate,Morlet wavelet analysis,and correlation analysis.Additionally,the Penman-Monteith formula was used to calculate the potential evaporation of the basin.And the relationship between evaporation from evaporation dishes and potential evaporation of the Songhua River basin was further analyzed by using sensitivity analysis,contribution rate calculation and correlation analysis.Drawing from the studies above,this thesis arrives at the following conclusions.(1)The evaporation from the evaporation dish in the Songhua River basin is unevenly distributed within the year,with the evaporation showing a monthly rising trend from January to May and a monthly decreasing trend from June to December.the mean evaporation reaches the maximum value of 8.58mm/d in May,which belongs to the period of strong evaporation.the minimum evaporation is less than 0.4mm/d in January,which belongs to the period of weak evaporation.The annual average evaporation is increasing significantly with the rate of 8.44mm/10 a,and the overall fluctuation is "decrease-increase-decrease-increase-decrease-increase".The trend of change,the abrupt change year occurred in 2018,the maximum value of historical evaporation was1878.29 mm,and the minimum historical value of 1267.41 mm occurred in 2013,the difference amounted to 610.88 mm.annual seasonally,the evaporation in spring showed a decreasing trend,in which the evaporation of spring evaporation dish accounted for 36%of the annual evaporation,and the evaporation of summer,autumn and winter evaporation dishes all showed an increasing trend,accounting for: 41%,19%,and 4%.Both annual and seasonal evaporation dish evaporation have a main cycle variation of about 30 years.(2)Spatially,the overall performance is the highest in the southwest,up to1800mm/a,especially in the area of Huolinguole,Zalut,Ulanhot,Baisheng,Tongyu,Changling,Solun and Tailai.The southeastern part is followed by the central part,and the northern part is the lowest.The overall fluctuation range of the annual average evaporation dish evaporation is 1300-1600mm/a.The overall fluctuation range of the evaporation dish evaporation in spring is 400-650mm/a,74% of the stations are decreasing trend,and mainly concentrated in the southwest of the Songhua River basin.In summer and autumn,most of the stations showed an increasing trend,and the overall fluctuation range of evaporation from the evaporation dish was 500-750mm/a and 200-380mm/a respectively.in winter,the overall fluctuation range was 30-90mm/a,and the evaporation amount was the largest in Zalut,Baisheng,Tongyu in the southeast region and in Erdao,Heilong and Yanji in the southwest region,and there was still an increasing trend.(3)Comparative analysis of the relationship between meteorological factors and evapotranspiration according to the partial correlation analysis shows that,for each meteorological factor,the meteorological factors affecting the annual evapotranspiration changes in the Songhua River basin on the annual scale are: relative humidity >temperature > sunshine hours > wind speed > precipitation.On the seasonal scale,spring is influenced by the significant decrease of wind speed more than the effect of warming and drying,which makes the evaporation in the Songhua River basin in spring show a decreasing trend.Summer: atmospheric temperature > humidity level > rainfall > sunlight hours;Autumn: humidity level > atmospheric temperature > sunlight hours;Winter:atmospheric temperature > humidity level > water vapor pressure > sunshine hours.During summer,autumn,and winter,the promoting effect of warming and increased sunshine duration on evaporation outweighs the significant decrease in wind speed,leading to an upward trend in evaporation during these seasons.(4)There are differences in the distribution of sensitivity of meteorological factors in the Songhua River basin.ET0 is the most sensitive to the change of Ea,followed by Rn and u.ET0 is the least sensitive to the change of T.T,Rn and u play a positive role in promoting the change of ET0,while Ea plays a negative role in suppressing it.On the seasonal scale,spring is the most sensitive to Ea;summer and autumn are more sensitive to T and Rn,and least sensitive to u;winter is more sensitive to u and Ea,but not to T and Rn.increase in T causes an increase in ET0,while u,Rn,and Ea cause a decrease in ET0,and the increase in ET0 is not enough to offset the decrease in ET0,resulting in a decrease in ET0 in the Songhua River basin,and the "evaporation paradox" also appears.The phenomenon of "evaporation paradox",i.e.,the temperature increases while the evaporation decreases.(5)The monthly scale variation and spatial variation characteristics of evaporation and potential evaporation in the basin evaporation dish are basically consistent.The correlation analysis method shows that the correlation between evaporation from evaporation dish and potential evaporation is high,and the potential evaporation increases with the increase of evaporation from evaporation dish,and the evaporation from evaporation dish is obviously higher than the potential evaporation,and the value of evaporation dish coefficient K of Songhua River basin is derived as 0.6. |
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