Temporal-spatial analysis on evapotranspiration of winter wheat in whole growth stage
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Abstract:
The spatio-temporal characteristic of evapotranspiration can not only quantify the water loss caused by evaporation,but also reflect the relationship between land use,water resource allocation and utilization.It was also an indispensable basic data for calculating the balance of agricultural water and soil resources,and planning,design and management of irrigation projects.With the increasing contradiction between water resources supply and demand and the refined requirements of modern irrigation and agricultural water management,it was necessary to illustrate evapotranspiration evolution rules on different spatial and temporal scales. To illuminate the changing laws of evapotranspiration in different growth stages of winter wheat,Yongnian District of Handan city was selected as the study area,and the validated regional SEBAL model through Penman-Monteith model was applied for simulating evapotranspiration.The mean square root of variance was 0.65 which shows that SEBAL model accuracy was higher,and the model can provide relatively accurate ET value for the study area.Based on this,SEBAL model was applied to simulate the evapotranspiration of wheat at different growth stages from October 2019 to June 2020,and the spatio-temporal evolution law of evapotranspiration in different growth periods of regional winter wheat was analyzed respectively. The maximum daily evapotranspiration during the whole growth stage of winter [JP2]wheat is from 0.97 mm/d to 13.66 mm/d,[JP]and the average one ranges from 0.52 mm/d to 8.06 mm/d;the evapotranspiration was low in the west and high in the east,which was consistent with the irrigation difference caused by terrain and hydrgeological characteristics in the study area. (1) The regional daily evapotranspiration rose with fluctuations during the whole growth stage of winter wheat;the evapotranspiration was relatively low from seedling stage to regreening stage,with the regional evapotranspiration ranging from 0.52 mm/d to 1.49 mm/d;from double ridge stage to booting stage,the evapotranspiration ranged from 3.18 mm/d to 4.47 mm/d;from jointing stage to mature period (the critical growth stage),regional evapotranspiration increased rapidly,ranging from 4.47 mm/d to 8.06 mm/d.Overall,the evapotranspiration was the largest in summer,followed by spring,and the evapotranspiration was the smallest in autumn and winter.(2) The evapotranspiration in Yongnian District had a certain degree of temporal and spatial differences.The peak of regional evapotranspiration was spatially shifted between the seedling stage and regreening stage.In terms of the different growing stages,regional evapotranspiration from flowering stage to mature period was higher than from double ridge stage to booting stage,and regional evapotranspiration from double ridge stage to booting stage was higher than from seedling stage to regreening stage.The evapotranspiration in the central and northern regions of Yongnian District was the largest,followed by the southeast region,and the evapotranspiration in the western region was lower.(3) In the selected whole growth period,the daily evapotranspiration of winter wheat had a significant power relation with the average value of LAI,and the R2 was as high as 0.88,which revealed the quantitative relationship that the evapotranspiration increases positively with the change of LAI in Yongnian District.When the root quantity was low,the fluctuation of evapotranspiration was also low;with the rapid growth of crops,the root quantity showed an increasing trend and the evapotranspiration also showed a curved increasing trend in fluctuations.
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