| The linear system model is established from regional scale with the incentive of downstream of Heihe annual average flow and the response of Normalized Difference Vegetation Index (NDVI) processed from NOAA/AVHRR satellite data. With the aquifer dynamics formula, the theoretical basis of the lag model is derived .And the lag processing of Ejina oasis to the downstream is simulated according to NDVI of the oasis from the year 2000 to 2008.The model showed that the downstream significant influences the oasis vegetation most in the next year and gradually decrease year by year in the after five years. It is analyzed that hysteresis effect controlled by the parameter factor of depth,permeability coefficient,specific yield and river distance is an embody of oasis ecosystematic self-maintenance function. Meanwhile, the vegetation environment ecosystem in the model has complexity reversibility and some persistence, while parameters of permeability and storage-release in groundwater aquifer effect significantly from which we can compensate water resource and utilize it rationally. |
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