Using GM (1,1) models to predict groundwater level in the lower reaches of Tarim River: A demonstration at Yingsu section

Grey System theory is a multidisciplinary theory dealing with those systems for which we lack information, which uses a black-grey-white color spectrum to describe a complex system whose characteristics are only partially known or known with uncertainty. From the point of view of grey system theory, the dynamic of groundwater level in the lower reaches of Tarim River is typical grey system, which maybe provides us one of methods to approach the problem. As an attempt, through demonstration at Yingsu section, the paper has comparatively studied the grey forecasting models to predict the groundwater level in the lower reaches of Tarim River. The conclusions are: (1) The grey forecasting models, which include equal and unequal time lag GM (1,1) model, are applicable models to predict the groundwater level in lower reaches of Tarim River. The accuracy test parameters, P and C for equal and unequal time lag GM (1,1) model both achieved the desired impact for prediction. (2) The forecasted depth of groundwater for each well by unequal time lag GM (1,1) model is somewhat less than that by equal time lag GM (1,1) model. If the average of forecasted depth of groundwater by the two kind models is regarded as the predicted result, the depth of groundwater of monitoring well C4, C5 and C6 in 2007 will be 4.1696 m, 4.317 m and 4.4839 m respectively, and that in 2008 will be 4.0612 m, 4.2308 m and 4.3604 m respectively.