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Lanzhou University (2022)

Estimation of Evapotranspiration under Soil Water Stress in Arid and Semi-arid Areas

徐绍源

Titre : Estimation of Evapotranspiration under Soil Water Stress in Arid and Semi-arid Areas

Auteur : 徐绍源

Grade : Master 2022

Université : Lanzhou University

Résumé partiel
Evapotranspiration(ET)is an important part of the land surface hydrological cycle and energy exchange process.It is also the key link between Soil Plant Atmosphere Continuum(SPAC).It affects the regional precipitation redistribution process and the regional water cycle and balance.In the arid and semi-arid areas with limited water resources and sparse in situ observations,finding accurate and easy methods of estimating ET is of great significance to the water security and rational planning of water resources in the region.In this study,the typical agro-pastoral ecotone and Qilian Mountain ranges in the arid and semi-arid regions of northern China were selected as the study areas to analyze the impact of soil water on the actual ET,determine the soil water stress threshold under different environmental conditions,and compare and evaluate the simulation performances of FAO56 Penman-Monteith(FAO56),Priestley-Taylor(P-T),Hargreaves and Samani(Har)ET estimation models.Two calculation methods of water stress coefficient,Campbell and Thompson,were analyzed to determine the suitable ET estimation scheme under soil water stress in the study areas.The main findings are as follows :(1)Affected by vegetation coverage and root system,the soil water stress thresholds are different in the two study areas.In the agro-pastoral ecotone,the vegetation coverage is low,with sparse distribution and underdeveloped root system,the soil water content is low,and the water stress occurs quite often.The water stress threshold is the field water capacity and wilting point corresponding to the soil moisture content of the in-situ observation stations,which is between 0.120 mm 3/mm 3 and 0.150mm 3/mm 3,0.020 mm 3/mm 3 and 0.030 mm 3/mm 3,respectively.In the Qilian Mountains,the vegetation coverage is high,the roots are relatively well developed,and the soil water content is high.The soil water stress threshold is basically the water content corresponding to the 90%and 10%percentile of soil water in the root area of the in-situ observation stations,which is between 0.400 mm 3/mm 3 and 0.451 mm 3/mm 3,0.010mm 3/mm 3 and 0.230 mm 3/mm 3,respectively.(2)In the agro-pastoral ecotone,the performance of P-T method is the best,with root mean square error(RMSE)of 1.780 mm·d-1,and mean average error(MAE)of1.208 mm·d-1.FAO56 is the second,with RMSE and MAE of 1.991 mm·d-1 and 1.665mm·d-1,respectively.Har is the worst,with RMSE and MAE of 8.345 mm·d-1 and 7.278mm·d-1,respectively.P-T excludes the influence of wind speed U on its estimation results,and is more suitable for sparse and complex underlying land surface.Its overall performance is the best in the study areas.Due to its unreasonable values of surface resistance and aerodynamic factor,FAO 56 has errors in ET estimation,and its performance is worse than P-T.Har has the worst performance in the study areas due to its excessively high temperature difference and empirical coefficients.(3)Affected by vegetation roots,the variation range of soil water is large,and the"three basepoints"Thompson method has a large estimation error when the water content is low.Campbell method only considers the upper limit of water stress threshold,excluding the impact of low soil water on the estimation results of stress coefficient.In the agro pastoral ecotone and Qilian mountain area,the performance of Campbell method is 1.4%and 8.3%higher than that of Thompson method,respectively.Campbell’s calculation method of soil water stress coefficient has the better performance than Thompson method in the study areas.

Mots clés : Evapotranspiration ;Agro-pastoral ecotone ;Qilian Mountains ;Water stress threshold ;Soil water stress coefficient ;

Présentation (CNKI)

Page publiée le 20 octobre 2022