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Xi’an University of Technology (2021)

Study on Vegetation Water Requirement of Typical Plantation and Grassland in Loess Gully Area

符冲

Titre : Study on Vegetation Water Requirement of Typical Plantation and Grassland in Loess Gully Area

Auteur : 符冲

Grade : Master 2021

Université : Xi’an University of Technology

Résumé partiel
Arid and semi-arid areas are sensitive areas under global climate change.As a typical semi-arid area,the gully area of the Loess Plateau is the most vulnerable area of the global ecosystem.The reality of serious water shortages makes it necessary to consider the water requirements level of the selected vegetation and whether the water requirements can be met when carrying out ecological management measures such as afforestation and grass planting in the area.At the same time,as mixed plantation begin to occupy a certain position in vegetation restoration,it is also an urgent problem to be solved to evaluate their water requirements.This study takes the Nanxiaohegou watershed,a typical small watershed in the loess gully area,as the research object.On the basis of field observations,according to the results of field observation and investigation,firstly divide the hydrological year of different rainfall years during the test period(2018,2019,2020).Then the applicability of the single and dual source ETO calculation model in the loess gully area was evaluated.Then use the dual crop coefficient principle to carry out the growth season daily-scale vegetation water demand estimation of Robinia pseudoacacia,Platycladus orientalis,Pinus tabulaeformis pure plantation and its mixed plantation of Robinia pseudoacacia-Platycladus orientalis、Robinia pseudoacacia-Pine tabulaeformis、Pinus tabulaeformis-Platycladus orientalis,Lonicera japonica Thunb plantation,natural Weeds and artificial Alfalfa grassland.Finally,while using the model to calculate the effective rainfall,the Crop Water Surplus Deficit Index is introduced to analyze the water demand satisfaction degree of different vegetation types,and an evaluation system of drought and flood indicators suitable for the loess gully area is established according to the actual situation.Finally came to the following conclusions :(1)In the single-source model analysis,the simulated value of the P-M model is used as the standard value.The unoptimized H-S model simulates too large a total amount of different hydrological years.The calculation results of Nash efficiency coefficient NSE,consistency coefficient d,and root mean square error RMSE all show that the simulation value does not meet the accuracy requirements.Optimize the H-S model through monthly linear regression,the coefficient a is distributed between-0.061 and 0.908,and the constant b is distributed between 0.318 and 3.726.The NSE of the optimized H-S model from dry years to wet years increased to 0.77,0.73,0.71 ;d increased to 0.93,0.92,0.91 ;RMSE decreased to 0.50,1.05,0.90.The deviation of the total amount from the standard value is greatly reduced to about 2%(1.70%~2.18%).The NSE,d,RMSE calculation results of the P-T model in different hydrological years show that the P-T model has reached the accuracy requirements,but the total amount of simulation values is too large.Adjust the coefficient α of the P-T model,and the final adjustment result is a=1.122.The NSE of the optimized P-T model from dry years to wet years increased to 0.86,0.95,0.95 ;d changed to 0.86,0.99,0.99 ;RMSE was reduced to 0.31,0.18,0.38.The total deviation from the standard value does not exceed 8%(4.69%~7.85%).Overall,the simulation accuracy of the optimized P-T model is higher than that of the H-S model.(2)S-W dual-source model and P-M model basically have the same trend of change(first increase and then decrease)

Mots clés : potential evapotranspiration ;vegetation types ;dynamic simulation ;vegetation water requirement and satisfaction ;Crop Water Surplus Deficit Index ;drought and flood grade ;

Présentation (CNKI)

Page publiée le 6 novembre 2021