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The effects of human activities on climate change are a significant area of research in the field of global environmental change. Land use and land cover change(LUCC) has a greater effect on climate than greenhouse gases, and the effect of farmland expansion on regional drought is particularly important. From the 1910 s to the 2010 s, cultivated land in Songnen Plain increased by 2.67 times, the area of cultivated land increased from 4.92×10~4 km~2 to 13.14×10~4 km~2, and its percentage of all land increased from 25% to 70%. This provides an opportunity to study the effects of the conversion of natural grassland to farmland on climate. In this study, the drought indices in Songnen Plain were evaluated from the 1910 s to the 2010 s, and the effect of farmland expansion on drought was investigated using statistical methods and the Weather Research and Forecasting Model based on UK's Climatic Research Unit data. The resulting dryness index, Palmer drought severity index, and standardized precipitation index values indicated a significant drying trend in the study area from 1981 to 2010. This trend can be attributed to increases in maximum temperature and diurnal temperature range, which increased the degree of drought. Based on statistical analysis and simulation, the maximum temperature, diurnal temperature range, and sensible heat flux increased during the growing season in Songnen Plain over the past 100 years, while the minimum temperature and latent heat flux decreased. The findings indicate that farmland expansion caused a drying trend in Songnen Plain during the study period. 相似文献
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清末耕地空间分布格局重建方法比较 总被引：4，自引：2，他引：2
揭示历史时期土地利用/覆盖变化是认识人类活动对气候和环境影响的基础。本文在耕地面积、人口数量、土地利用及森林分布等多源数据基础上,分别以近代耕地空间分布格局和历史时期耕地潜在分布区为边界条件,通过构建耕地垦殖倾向指数模型分配耕地面积,在1 km×1 km象元尺度上重建了清末(1908年)松嫩平原耕地空间格局,并对重建结果进行分析比较。结果表明:1两种方法重建的耕地空间分布范围格局基本一致,耕地空间定位吻合率约为68%。清末(1908年)耕地集中分布在松嫩平原东部和南部地区;2以历史时期耕地潜在分布为边界条件的重建结果,较以近代耕地空间分布格局为限制范围的重建结果更准确,更符合历史事实。 相似文献
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Reconstruction of cropland spatial patterns and its spatiotemporal changes over the 20th century on the Songnen Plain,Northeast China 总被引：1，自引：0，他引：1
We initially estimated the cropland area at county level using local historical documents for the Songnen Plain (SNP) in the 1910s and 1930s. We then allocated this cropland area to grid cells with a size of 1 km × 1 km, using a range of cultivation possibilities from high to low; this was based on topography and minimum distances to rivers, settlements, and traffic lines. Cropland areas for the 1950s were obtained from the Land Use Map of Northeast China, and map vectorization was performed with ArcGIS technology. Cropland areas for the 1970s, 1980s, 1990s, 2000s, and 2010s were retrieved from Landsat images. We found that the cropland areas were 4.92 × 104 km2 and 7.60 × 104 km2, accounting for 22.8% and 35.2% of the total area of the SNP in the 1910s and 1930s, respectively, which increased to 13.14 × 104 km2, accounting for 60.9% in the 2010s. The cropland increased at a rate of 1.18 × 104 km2 per decade from the 1910s to 1970s while it was merely 0.285 × 104 km2 per decade from the 1970s to 2010s. From the 1910s to 1930s, new cultivation mainly occurred in the central SNP while, from the 1930s to 1970s, it was mainly over the western and northern parts. This spatially explicit reconstruction could be offered as primary data for studying the effects of changes in human-induced land cover based on climate change over the last century. 相似文献
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为准确评估锈蚀钢框架在地震作用下的损伤,对已有的地震损伤模型进行改进,并对框架柱的地震损伤特性进行分析。建立基于变形和能量组合的双参数损伤模型,对损伤模型中相应的参数给出具体定义和表达式,定义不同破坏等级的损伤指数范围。对3个具有不同锈蚀率的空间钢框架结构进行弹塑性时程分析,并对损伤模型的准确性进行验证。研究结果表明,该模型能够较好地描述锈蚀钢框架柱的地震损伤程度。研究结果可为该类结构构件的地震损伤评估以及基于损伤的抗震设计方法的建立提供理论依据。 相似文献
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等效框架模型采用宏观模型来模拟砌体墙在平面内的抗震性能。砌体墙的墙柱和墙梁采用同时考虑轴向弯曲和剪切变形的基于力法的纤维截面进行模拟，且两者的连接视为刚性区域。轴向压缩及弯曲效应在截面纤维模型中考虑，而剪切效应由V-γ剪切恢复力模型表达，弯曲和剪切在单元层面进行耦合。通过统计和分析，确定骨架曲线的计算方法，并基于Ibarra-Krawinkler模型提出剪切恢复力模型。通过算例得出:该模型在单调加载和循环加载下的数值计算结果与试验结果均吻合较好。 相似文献
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Accuracy assessment of approaches to spatially explicit reconstruction of historical cropland in Songnen Plain,Northeast China 总被引：1，自引：1，他引：0
To understand historical human-induced land use/cover change (LUCC) and its climatic effects, it is essential to reconstruct historical land use/cover changes with explicit spatial information. In this study, based on the historically documented cropland area at county level, we reconstructed the spatially explicit cropland distribution at a cell size of 1 km × 1 km for the Songnen Plain in the late Qing Dynasty (1908 AD). The reconstructions were carried out using two methods. One method (hereafter, referred to as method I) allocated the cropland to cells ordered from a high agricultural suitability index (ASI) to a low ASI, but they were all within the domain of potential cropland area. The potential cropland area was created by excluding natural woodland, swamp, water bodies, and mountains from the study area. The other method (hereafter, method II) allocated the cropland to cells in the order from high ASI to low ASI within the domain of cropland area in 1959. This method was based on the hypothesis that the cropland area domain in 1959 resulted from enlargement of the cropland area domain in 1908. We then compared these two reconstructions. We found that the cropland distributions reconstructed by the two methods exhibit a similar spatial distribution pattern. Both reconstructions show that the cropland was mostly found in the southern and eastern parts of the Songnen Plain. The two reconstructions matched each other for about 68% of the total cropland area. By spatially comparing the unmatched cropland cells of the two reconstructions with the settlements for each county, we found that unmatched cropland cells from method I are closer to settlements than those from method II. This finding suggests that reconstruction using method I may have less bias than reconstruction with method II. 相似文献
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