Modelling on multiyear lag of Ejina Oasis vegetation behind Heihe river´s runoff

A linear system model was set up on a regional scale by regarding annual average runoffs of downstream Heihe River as incentives to the eco-system, and MODIS/Terra monthly NDVI (Normalized Difference Vegetation Index) data as responses from the system. With aquifer hydraulics mechanism analysis, the theoretical basis of the lag model was derived on a solution of one-dimensional river-land groundwater flow definite solution problem, and the lag processing of Ejina Oasis vegetations to the downstream runoffs was simulated according to NDVTs of the oasis from the year 2000 to 2009. It is recognized that the lag process is controlled by the aquifer factors such as hydraulic conductivity, specific yield and distance to the river, and is an embodiment of oasis eco-systematic self-maintenance function.