| Mahai basin, an inland basin in Northwest China, is located at the northern marginof Qaidam Basinin, Qinghai Province. Due to the lack of rainfall and the strongevaporation, water resource shortage, ecological environment is extremely fragile.The low vegetation cover in desert oasis, its growth is closely related to groundwaterdepth and ecological conditions. Along with the increasing human activities in recentyears, a lot of exploitation of groundwater has caused degradation of oasis vegetation.Therefore, the study on the effect of the level of oasis ecological groundwater onhuman’s activities is essential for providing a theoretical support on the sustainableutilization of water resources in Mahai basin, establishing effective protection policyof ecological environment and sustainable development in Northwest ChinaThis article, by means of MODIS and GIMMS NDVI remote sensor data, analyzesthe annual and seasonal trend of changes on oasis vegetation of dessert, and does theanalysis on the spatial distribution characteristics. We analyze the rainfalls andtemperature records of this area in41years that from the year1970~2010bywavelet-analysis technique and distance-average analysis technique, to discloserecords’ characteristics, comparing with the analysis on the changing trends.According to hydrology information and models established by GMS software, weforecasted how the flowing field of Mahai basin would be changed by different meansof exploitation. Using the Spatial Analyst Module under ArcGIS software system, weanalyze the relationship between the average data with different depths ofgroundwater, to make sure the location of groundwater under oasis and to predicatethe changes of oasis on basis of equation module in kinds of excavating situation.The major conclusions from this article could be stated as below:(1) The vegetation growth trend of the oasis in Mahai basin shows a declining trendin recent30years from1982to2009. In the spatial distribution aspect, almost1/3area of the oasis vegetation appeares signs of slowly growth recession.(2) The rainfalls data showed a wavelike appearance in the past41years, therainfall increased significantly from2000to2009. In terms of temperature changes,Mahai basin showed a raising trend in the past41years and the raising rate was0.32℃/10a. In dimensions by years, the changes of oasis of Mahai showed anirrelevancy to rainfalls and temperature. (3) The ecological groundwater depth which is suitable for vegetation growth isabout3-4.5m through quantitative study in deser oasis of Mahai Basin. The resultdiffered from the previous studies in Ejina and the Yinchuan plain results, whichmaybe most probably caused by different climate, hydrology and the soil.(4) By constructing the numerical model for Mahai basin groundwater, andanalyzing groundwater level changes in different mining scenarios in the study areas,the results showed that: the usages of Yuka coal mine and power plant had a limiteffect to the groundwater resource and groundwater’s flowing field, for their usedquantity was small. The expoitation of postassium salts had a large effect onto thegroundwater system, no matter whether we took ashallow-solving excavating methodor a deep-confined brine exploitation method.(5) Forecasting the growing changes of oasis in different mining sceneria, the resultshowed that: in case of the salt lake had not been exploited, the oasis would have ahealthy growth and its NDVI was among0.3-0.5. The Yuka coal mine, together withpower plant and the waterflood utilization in northwest zone, the oasis index numberchanged slightly, while, the deep-confined water exploitation method in salt lake, hada large affect on oasis’growth. |
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