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中国草原牧区和半牧区草畜平衡状况监测与评价 总被引：7，自引：0，他引：7
草原超载过牧是造成我国草原大面积退化、沙化的主要原因之一,草畜平衡监测、评价和管理是实现我国草原植被恢复和重建的关键,也是研究的热点和难点。本文采用遥感和地面调查相结合的方法从宏观上监测和评价了农业部认定的264个牧区和半牧区县的草畜平衡状况,主要结论如下:(1)2008年监测区平均草畜平衡指数为33.58%,总体处于超载状态;(2)120个牧区县草畜平衡指数为27.37%,144个半牧业县为42.07%,半牧区县是我国实行草畜平衡管理的重点和难点;(3)六大牧区中牧区县2008年超载程度排序为:甘肃>四川>新疆>青海>西藏>内蒙古,半牧区县超载程度排序为青海>西藏>内蒙古>新疆>四川>甘肃。本文所得结论可为我国草原资源管理和保护提供参考价值和借鉴意义。 相似文献
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Based on TM image data and other survey materials, this paper analyzed the spatiotemporal patterns of land use change in the
Bohai Rim during 1985–2005. The findings of this study are summarized as follows: (1) Land use pattern changed dramatically
during 1985–2005. Industrial and residential land in urban and rural areas increased by 643,946 hm2, of which urban construction land had the largest and fastest increase of 294,953 hm2 at an annual rate of 3.72%. (2) The outward migration of rural population did not prevent the expansion of residential land
in rural areas by 184,869 hm2. This increase reveals that construction of rural residences makes seriously wasteful and inefficient use of land. (3) Arable
land, woodland and grassland decreased at a rate of −0.02%, −0.12% and −1.32% annually, while unused land shrank by 157,444
hm2 at an annual rate of −1.69%. (4) The change of land use types showed marked fluctuations over the two stages (1985–1995 and
1995–2005). In particular, arable land, woodland and unused land experienced an inversed trend of change. (5) There was a
significant interaction between arable land and woodland. Industrial construction land in urban and rural areas showed a net
trend of increase during the earlier period, but only adjustment to its internal structure during the second period. The loss
of arable land to the construction of factories, mines and residences took place mainly in the fringe areas of large and medium-sized
cities, along the routes of major roads, as well as in the economically developed coastal areas in the east. Such changes
are closely related to the spatial differentiation of the level of urbanization and industrialization in the region. 相似文献
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The Webb-Resio-Tracy (WRT) method for exact computation of the non-linear energy transfer rate was implemented in MASNUM-WAM, which is a third-generation wave model solving the discrete spectral balance equation. In this paper, we describe the transformation of the spectral space in the original WRT method. Four numerical procedures were developed in which the acceleration techniques in the original WRT method, such as geometric scaling, pre-calculating, and grid-searching, are all reorganized. A series of numerical experiments including two simulations based on real data were performed. The availability of such implementation in both serial and parallel versions of the wave model was proved, and a comparison of computation times showed that some of the developed procedures provided good efficacy. With exact computation of non-linear energy transfer, MASNUM-WAM now can be used to perform numerical experiments for research purposes, which augurs well for further developments of the model. 相似文献
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LAGFD-WAM海浪数值模式是一种第三代海浪数值模式，通过求解波数谱平衡方程，并考虑风输入、波浪破碎耗散、底摩擦耗散、波波非线性相互作用和波流相互作用等源函数，模拟波数空间下的海浪方向谱，并依此获得海浪的波高、周期和平均波向。该模式的一个显著特点是采用特征线嵌入格式求解海浪的传播。在进行浅水区域的海浪模拟时，特征线嵌入格式的数值计算方案是否合理对海浪数值模拟结果产生直接的影响。为此LAGFD-WAM海浪数值模式提出了一种新的特征线混合数值计算格式，并应用于浅水海浪数值模拟。结果表明，采用该计算方法，能够使数值模拟结果与实测结果很好符合。 相似文献
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浅水环境下波浪能能流密度计算方法研究 总被引：2，自引：0，他引：2
本文列举了3种波浪能能流密度计算方法,通过实测资料和数值模拟的实验,分析了3种方法在浅水环境中的适用性。分析得知,定义方法对浅水环境中的海浪特征考虑最为周全,计算结果最准确,但强烈依赖海浪谱的存在,适用面较窄;经验方法仅依赖常规海浪参数,对各种基础资料几乎都适用,但对波能能流密度的估计往往偏低,且不能明显反应出地形抬升对波能能流密度的汇聚效应;修正方法考虑了浅水的影响,通过适当的选取参数,可以给出较准确的结果,但对于大的波能能流密度值存在过高估计的问题。3种计算方法各有优劣,可以根据实际需要适当选择。 相似文献
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吴晓春 《地理与地理信息科学》1987,(2)
从国土经济学和资源经济学来说,土地是一种宝贵的基本资源。对土地的研究不仅要从自然科学角度,还要从社会经济科学角度进行。本文依据马克思主义关于土地生产力学说,从土地作为生产资料,具有“双重性”出发,通过生产力构成的剖析,对土地自然属性和经济属性加以综合,以合理评价土地生产力。 一、评价原理 土地作为一种资源,重要的是在于其自然的利用过程,亦即广义的土地农业利用,表现在土地资源的再生性是区别于建设用地的重要标志,土地资源评价的实质是确定土地的生产能力,亦即土地的生产力。马克思主义的土地生产力学说,认为土地生产力由两方面决定的, 相似文献