石羊河流域中下游绿洲土地利用变化与水资源动态研究

根据1986年和2000年的TM影像数据,利用地理信息系统(GIS)技术通过景观斑块的转移矩阵计算,分析了石羊河流域凉州区和民勤两个典型绿洲近15年来的土地利用变化;并利用不同时期中下游绿洲水资源量和开发利用程度,结合种植业结构,分析了该区域水资源利用动态变化。结果表明,耕地大量增加,凉州区和民勤绿洲分别增加了6302 hm2和36434 hm2,民勤绿洲林地大面积减少,2000年林地面积仅为1986年的55%,绿洲面积减少了23365 hm2;而中游凉州区绿洲面积却增加了8167 hm2;上下游用水量之比从20世纪50年代的1.612急剧增大到90年代的8.33,用水矛盾日益突出,下游水库来水量40年来下降达63.1%;地下水开采强度日益增加,机井分布密集,地下水位大幅度下降;种植业结构不合理,耗水量较大的粮食作物所占的比例过大。

Dynamics of water resources and land use in oases in middle and lower reaches of Shiyang River watershed, Northwest China

Based on the TM image of the oases in Liangzhou District and Minqin county in middle and lower reaches of Shiyang River in 1986 and 2000,this paper calculates the transformation matrix of the landscape mosaics,and analyzes the relationship between the land use changes and the dynamics of runoff and groundwater resource and their exploitation in the two oases. The results show that:(1)Farmland area expanded distinctly by 6302 hm2 in Liangzhou and 36434 hm2 in Minqin oasis. And the transition of landscape elements in Minqin oasis is developing toward desertification,with the area of 23349 hm2 turned into desert land,however it is also developing toward the other way-the oasis landscape expansion by 81581 hm2 in Liangzhou oasis.(2)The ratio of the utilized water quantity in the upper and middle reaches to that in lower reaches increases great from less than 2 before 1970 to more than 8 since 1995;the annual recharge quantity to the Hongyashan reservoir decreases by 63.1% in recent 40 years.(3)Groundwater exploitation develops progressively,and the density of water-supply wells increases remarkably,up to 5.7 and 1.8 wells/km2 in Liangzhou and Minqin oases respectively in 2000;and the groundwater table drops obviously,the lowering rates reach up to 0.6-0.8m/year in some place.(4)the cropping patterns in the study area are distributed irrationally,too.If the planting percentage of water-wasting crops drops to 50% in both oases, it can save irrigating water by 1.2×108m3 in Liangzhou oasis and 0.2×108m3 in Minqin oasis one year.