| The purpose of this paper is to detect the dynamics of underground water system in a typical Loess Tableland named Dongzhi (DLT) and analyze local water demand and supply by using a systematically trained WEAP model. Meteorological Time series in the DLT was tested by M-K approach and wavelet analysis method for a general illustration of the hydrometeorology in the study area. According to the hydrogeological characteristics of the DLT, the underground water system was conceptually divided into two parts as the upper soil water reservoir (SWR) and the deeper groundwater reservoir (GWR). The monthly dynamic of the SWR was defined by a hydrologic model named SWAT combined with remote sensed methods while the GWR was quantified by groundwater dynamics method for the spring overflow combined with the survey data of well abstraction. Studies above helped to clarify the transfer mechanism among water from atmosphere, in the SWR and the GWR. Based on which, the WEAP model was parameterized and trained for the regional water utilization analysis, according to that, a best water allocation scenario was defined from eight scenarios from combinations of three dramatic influential factors on water utilization in the DLT. Main conclusion are followed as:(1) It is found that the air temperature increased with a decadal ratio of0.36℃/10a while the regional precipitation decreased with a decadal ration of9.58mm/10a. M-K test suggested the air temperature catastrophe appeared in1993while it was unclear for the trend analysis of the precipitation. Wavelet analysis resulted main periods orderly of33,9and4years for the air temperature and3,13,8and20years for the precipitation.(2) According to the results from SWAT modeling and remote sensed methods, supply from precipitation to the SWR mainly occurred during the time period of June to September (rainy season in the DLT, precipitation supply in the period occupied92.25%to the annual total) while the land surface evapotranspiration (ETc) occurred mainly from April to October (growing season in the DLT, ETc in this period occupied93.20%to the annual total). It was found that ratio of increase of the precipitation supply (1.55%) was much less than that (19.89%) of the land surface ETc. The SWR experienced mainly a negative balance especially in May and June over the past30years.(3) Vertical recharge including SWR transfer and rainfall percolation to the deeper GWR maintained decrease, with a reduction of34%in2000s when compared with that in1980s, while well abstractions increased by49.38%, both negatively drove the groundwater level an accumulative drawdown of15.7m and also, the spring overflow declined by an overall36.50%in the past30years.(4) Along with the social economy survey and forecasting, the WEAP model was parameterized and trained for the scenarios analysis of water utilization in the DLT. The best water demand and supply strategy was defined based on eight scenarios comparison which identify the three main factors influencing future water allocation. The best water use framework makes water supply and demand balance in most of the planning years, meant a satisfactory practice to the social water utilization.The study is probably a case example for underground water system quantification and rational utilization of water resources in the area of semi-arid loess tableland. |
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