Spatio-Temporal Variations And Influential Factors Of Evapotranspiration In Kekesu Wetland

Evapotranspiration(ET)widely exists in the surface ecological process.Surface evapotranspiration is an important link between surface ecosystem and hydrological process,which affects the regional climate change and water resource distribution.So,surface evapotranspiration plays an important role in study of water cycle system and water resource management.In this paper,we analyzed the evapotranspiration changes of the Kekesu wetland ecosystem at different time scales,which measured by the eddy covariance open system in 2018-2019.And we also analyzed the spatial distribution characteristics of evapotranspiration,which estimated based on the relationship between MODIS-NDVI data and evapotranspiration.While,the influencing factors of the spatio-temporal variation of evapotranspiration were discussed.The results show that:(1)Daily evapotranspiration increases gradually after sunrise and decreases gradually at sunset basically.In different months,daily evapotranspiration starts to increase at different times.Diurnal variation of evapotranspiration showed a regular trend of 2018-2019 in Kekesu wetlands,with the maximum evapotranspiration from 11:00 AM to 16:00 PM.And the minimum evapotranspiration were in the morning and evening.The annual peak of hourly variation in daily evapotranspiration occurred at 15:00 PM in July,and was 0.55mm/h in 2018 and 0.58mm/h in 2019.From June to September,the average daily evapotranspiration was less than 0.1mm/h from 23:00 to 8:00.In the monthly and annual variation of evapotranspiration,plant growth reached its peak in July of each year,and with the highest values occurring on July 9,2018(15.64mm/d)and July 1,2019(13.57mm/d).The highest values of the total evapotranspiration in July were 313.31mm in 2018 and 302.54mm in 2019,accounting for 27.72%and 26.20%of the annual evapotranspiration.In the non-growing season,vegetation coverage was low and evapotranspiration was remained low too from October to December.The total evapotranspiration was 1130.07mm in 2018 and 1154.53mm in 2019.The total ET was 24.46mm(2019)higher than that in 2018,accounting for 2.12%of the total evapotranspiration in 2018.(2)The vegetation coverage in Kekesu wetland is relatively good.The average NDVI from April to October is 0.50 in the whole region in 2018-2019,of which,the vegetation NDVI from June to July is the highest in northwest Kekesu wetland The NDVI in June and July in 2019 is higher than 0.8,and 3.80%and 2.90%higher than that in 2018 respectively.The correlation coefficient between NDVI and evapotranspiration has a positive correlation between NDVI and ET.The formula of fitting curve is Y=253.45x+0.6231(R2=0.89)(where X is NDVI and Y is ET).According to the correlation between NDVI and evapotranspiration,the spatial variation value of evapotranspiration was inverted.The distribution of evapotranspiration in the spatial variation of the average evapotranspiration of the wetland is mainly concentrated in the northwest direction,while the distribution in the southeast is relatively small.The monthly average evapotranspiration in the whole region were 126.35mm(2018)and 126.86mm(2019)respectively.The change rate of evaportranspiraion was about-36?0mm.a-1.The highest proportion of the whole region was 27.90%.In the growing season,evapotranspirationwas significantly different in different regions of the Kekesu wetland.Precipitation was rare,and vegetation was sparse in the southeast region,ET became small While vegetation was lush and ET became larger in the central plain region.(3)Precipitation and relative humidity were the most sensitive to evapotranspiration in 2018 to 2019.The sensitivity of precipitation and relative humidity were 44.10 and 18.09 respectively.And the sensitivity of air temperature,wind speed and saturated water pressure were low.Although the sensitivity coefficient of the difference between air temperature and saturated water pressure is small,the contribution rate of air temperature to evapotranspiration is up to 51.65%.And the contribution rate of saturated water pressure to evapotranspiration is 15.33%.The air temperature and saturated water pressure was positively correlated with evapotranspiration(R2=0.78,P<0.01;R2=0.86,P<0.01).Therefore,the main factors affecting evapotranspiration in Kekesu wetland were the air temperature and saturated water pressure.