KMS XINJIANG INSTITUTE OF ECOLOGY AND GEOGRAPHY，CAS
| 三江平原耕地结构演化及其对粮食产量和地表热环境的影响研究 | |
| Alternative Title | Evolution of the cropland structure and effects on grain production and land surface thermal environments in the Sanjiang Plain, China |
| 潘涛 | |
| Subtype | 博士 |
| Thesis Advisor | 张弛 |
| 2020-06-30 | |
| Degree Grantor | 中国科学院大学 |
| Place of Conferral | 北京 |
| Degree Discipline | 理学博士 |
| Keyword | 耕地结构 土地制度区 粮食安全 地表热环境 三江平原 Cropland structure Land system Food security Surface thermal environment Sanjiang Plain |
| Abstract | 三江平原是中国商品粮生产基地和耕地改革先行示范区， 其耕地变化代表着东北地区乃至全国农业用地改革的方向。该区域耕地的快速扩张必然对粮食产量和农业环境产生重大影响。此外，三江平原也是中国不同土地制度典型区，辖区由国营农场区和普通农户区组成。 开展对三江平原耕地结构演化及其对粮食产量和地表热环境的研究，有利于了解中国农业用地改革过程、粮食安全问题、和农业环境问题。同时也有利于了解不同土地制度对这些问题的潜在影响。本研究从土地利用、 土地管理制度、粮食产量、和地表热环境四个方面确定研究目标。 (1) 基于陆地资源卫星，追踪时间序列的整个研究区耕地面积及其结构变化，还原三江平原耕地垦殖历史； (2) 在水田发展背景下，比较不同土地制度管理区过去耕地变化和未来发展格局，探究土地制度对耕地演化的影响； (3) 揭示在全球农业贸易和中国宏观农业政策背景下，该区域耕地变化对粮食产量影响的时空特征，以及不同土地制度区农作物演化和粮食变化差异； (4) 定量分析耕地结构演化对地表热环境的影响，揭示不同农作物在生长季的温度差异，探究寒冷地区水田扩张的“冷岛效应” 。针对这四个目标， 本研究结论如下：(1) 基于一种土地利用更新方法， 采用 771 景陆地资源卫星对 1990-2015 年时序间隔 5 年的耕地演变进行了追踪分析。结果表明：三江平原的陆地资源卫星影像支持多年的土地制图要求。 基于新的土地利用产品， 三江平原耕地总面积由 45 252.01km（2 1990）持续增长到 58 231.59 km（2 2015）。从耕地结构分析，水田面积由 2 850.87km2（1990） 快速增长到 26 537.14 km2（2015） 。这使得水田在耕地总面积的占比由6.30%（1990） 几乎直线上升到 45.57%（2015） 。这说明三江平原耕地结构发生了剧烈变化， 该变化以水田快速扩张为主要特征。(2) 在水田快速扩张背景下，分析了 1990-2050 年不同农业制度区耕地的历史变化状况和未来发展格局。结果表明：国营农场水田扩张速度快于普通农户区，对应速率分别为 648.61 km2/yr 和 298.84 km2/yr。这使得在 1990-2015 年间，国营农场水田发展从初始阶段进入末期阶段，而普通农户区则从初始阶段进入中期阶段。 根据预测， 2020-2050 年，水田发展重心从国营农场迁移到普通农户区， 这也导致了普通农户区旱地出现大量流失。 本研究提供了遥感卫星证据，表明国营农场通过水田面积扩张来影响耕地种植模式，形成与普通农户区差异化的耕地结构演化格局。(3) 基于土地转换、作物演化、粮食单产、模型模拟等信息，揭示不同土地制度区在谷物生产中的角色分工。结果表明：在 1990 年研究区粮食总产量为 748.03×104t，到 2015 年增长到 3 785.13×104 t，表明总产量增长了 4.06 倍。通过土地利用转移矩阵分析，旱地变成水田是 1990-2015 年间研究区主要的土地利用变化类型。 这种土地转变对粮食产量产生了积极影响，贡献了粮食总增量的 14.29%。 在 1990-2015年，三江平原农作物变化特征为：水稻和玉米在耕地的占比分别提高 33.67%和17.91%，而大豆和其他作物在耕地的占比则分别降低 25.93%和 25.65%。在不同的农业制度区，优势农作物的演变状况不同，在国营农场区由大豆（1990-2000）演化为水稻（2000-2015），而在普通农户区由大豆（1990-2005）演化为玉米（2005-2015）。不同的农作物演化特征表明： 国营农场对中国居民的口粮贡献更大， 而普通农户区的粮食侧重于为工农业生产服务，体现了不同的粮食生产角色分工。(4) 我们分析旱地作物转变为水田对地表环境的影响。 2000-2015 年期间，与旱地作物相比，新扩张的水田在生长季产生了高达 7.17±1.05℃的“冷岛效应” 。该“冷岛效应” 在 5 月/6 月达到高峰，在雨量充沛的 8 月降至最低。低密度、中密度和高密度水田区的地表温度分别降低了 0.59±0.06℃、 0.77±0.07℃和 1.08±0.08℃，说明随着水田密度的增加，该效应加剧。地表热过程机制表现为：在旱地被水田替代后，显热通量和土壤热通量分别降低了 52.94W/m2和 15.26W/m2，潜热通量和净辐射分别增加了 115.66W/m2 和 47.34W/m2。本研究的方法创新和主要发现如下： 首先，提供一个土地利用更新方法获得 30米分辨率耕地结构信息，该方法显示出较好的精度。其次， 在不同的土地制度管理区， 国营农场通过水田面积扩张来影响耕地种植模式，形成与普通农户区差异化的耕地演化格局；第三，旱地变成水田对粮食安全具有积极影响， 并揭示不同土地制度区农作物演化差异，阐明其在中国谷物市场供给中的角色分工； 最后，分析中国寒冷地区旱地变成水田在生长季的地表温度差异， 量化寒冷地区水田扩张的“冷岛效应” ，揭示其对地表热环境影响的内在机制。 |
| Other Abstract | Cropland evolution is one of the main land-use/cover changes in the world. In recentdecades, although cropland expansion has occurred in many places, the maintenance ofglobal cropland area is still a challenge worldwide under the backgrounds of urbanization,industrialization, rural development, and natural environment constraints. While thecropland needs to provide more agricultural products to meet the demand of populationgrowth. The issues are more serious in the world's most population country, China. In thepast few decades, China has successfully supported about 20% of the world's populationwith only 7% of the world's cropland through a series of cropland reform measures,indicating that the acute cropland changes happened in China. Sanjiang Plain is the nationalcommodity grain production base and the priority region of cropland reformation. Thus, thisregion is a hotspot for land-use/cover changes, accompanied by the high-speed extension ofagricultural land in conjunction with the large-scale loss of wetlands and unused land. Therapid cropland expansion brings about the significant impact on grain production andagricultural environment. Furthermore, Sanjiang Plain is also a typical region of differentland systems in China, which consists of state and private farms. It is convenient toinvestigate the effect of land systems on cropland evolution.In this study, we tracked time series of cropland changes and their impact on the grainproduction and the land thermal environment. The four research objectives of this study areas follows: (1) to track the analysis of cropland evolution derived from Landsat images; (2)to compare the past cropland structure changes with future patterns in different agriculturalsystems under backgrounds of paddy development; (3) to reveal the changes in grainproduction and the different grain roles of state and private farms in food supply market; (4)to quantify the cooling effect of rice paddy in cold region of China and compare thedifference of land surface thermal environment indicators between upland crops and paddyfield.(1) We tracked time series of cropland evolution derived from land resource satelliteimages during 1990-2015 across Sanjiang plain using an updated land use methodology.Results showed that the Landsat images in Sanjiang Plain supported the multi-year land userequirements with available image of over 700 scenes. Among them, the 222 images infocused six years and the auxiliary 44 images in other years were together to finish the land use maps. The overall accuracies of the updated land use methodology from the studyexhibited 89.50%, 91.25%, 90.78%, 91.78%, 92.22%, and 93.98% in years of 1990, 1995,2000, 2005, 2010, and 2015, respectively. According to the land use product, total croplandarea constantly increased from 45,252.01 km2 (1990) to 58,231.59 km2 (2015). Most ofnewly expanded croplands were located on flat plains, with low-lying landscapes and highproportions of swamps, rivers and ditches. For the cropland structure, paddy field expandedpersistently from 2850.87 km2 (1990) to 26,537.14 km2 (2015), with the proportions ofpaddy field to total cropland area continuously increasing from 6.30% to 45.57%. In contrast,the areas covered by upland crops presented obviously downward trend with areas from42404.14 km2 (1990) to 31694.45 km2 (2015). The acute cropland structure changesoccurred in Sanjiang Plain of China, accompanied by rapid paddy field expansion.Comparing with the current land products, including MODIS, ESA-GlobCover, Globalcover30, and NLCD, the cropland results from the study displayed better spatial patterns andprovided more accurate cropland dynamic information.(2) The past cropland structure changes with future patterns under different agriculturalsystems during 1990-2050 were analyzed under the backgrounds of rice paddy development.Results showed that a faster rice paddy expanding rates happened in state than private farms(648.61 km2/yr vs, 298.84 km2/yr), which led to the paddy development from initial stage(1990) to later stage (2015) in state farm, and from initial stage (1990) to middle stage (2015)in private farm, respectively. Under the backgrounds of paddy development, both privateand state farms experienced rapid cropland expansion with five-year increments during1990-2015, while the proportion of croplands covered by upland crops continuouslydecreased, with more loss in state than private farms. For the paddy development in theperiod of 2020-2050, paddy expansion is still faster in state farm than that of private farmduring 2015–2020. While the center of paddy development will be shifted to private farmfrom state farm during 2020-2050, leading to the greater losses of upland crops in privatethan state farms during 2020-2050. From landscape ecology perspective, with paddydevelopment from initial stage to late stage, rice paddy indicated an improvement in its patchadvantage and most of paddy patterns become aggregated, while upland crops lost the patchdominance and most of patterns became in the scattered ways. The results also showed thatall the changes in landscape ecology indices were greater in state than private farms.(3) We focused on the grain production changes and revealed the different grain rolesof different agricultural systems in grain supply market, from the comprehensive arrangement of land transformations and crop yields during 1990-2015. Results showed thatthe total grain production increased from 748.03× 104 t (1990) to 3785.13× 104 t (2015),which indicated that grain production was 4.06 times greater in 2015 than that in 1990. Theprincipal land use change, namely the land transformation from upland crops to paddy field,contributed 14.29% of total grain increment, indicating the positive effect on food safety. Ahigher contribution rate occurred in state than private farms, with values of 25.71% and6.48%, respectively. The evolved crops changed acutely, with grain ratio of rice paddy andcorn increased by 33.67% and 17.91%, and soybean and other crops decreased by 25.93%and 25.65 % during 1990-2015. Dominant crop was tracked with changing from soybean(1990-2005) to corn (2005-2010), and then to rice paddy (2010-2015) across Sanjiang Plain.In different farming regions, the dominant crop evolved from soybean (1990-2005) to corn(2005-2015) in private farm, and from soybean (1990-2000) to rice paddy (2000-2015) instate farm, indicating that state farm acted as the role for human diet supply and private farmmainly served for industrial and agricultural production.(4) The large-scale evolution of cropland structure from rain-fed farmland to paddyfield in Cold China could profoundly alter the land-surface thermal environment, as revealedby our synergetic investigation based on land-use data, remotely sensed images, and landsurface thermal dynamic models. During 2000-2015, drastic cropland structure changes tookplace across the study area, leading to rapid rice paddy expansion, most of which wereconverted from rain-fed farmland. Compared to the rain-fed farmland, the newly expandedpaddy field generated a cooling effect up to 7.17 ± 1.05 ℃ during the growth season. Thecooling effect peaked in May/June and minimized in August when rainfall was abundant.The effect was also correlated with paddy field density, reducing the LST by 0.59±0.06 ℃ ,0.77±0.07 ℃ , and 1.08±0.08 ℃ in the areas with low-, medium-, and high-density paddies,respectively. The underlying mechanisms could be explained by the changes in land-surfacethermal processes that accompanied the cropland conversion: when rain-fed farmland wasreplaced by paddy field, the sensible heat and soil heat fluxes decreased by 52.94 W/m2 and15.26 W/m2, respectively, while the latent heat flux and net radiation increased by 115.66W/m2 and 47.34 W/m2, respectively.The dissertation tracked time series of cropland evolutions across the Sanjiang Plainand in the different agricultural systems. The effect of cropland changes on grain productionand land surface thermal environment were further investigated. In this process, someinnovations involving the methodologies and results were provided as follows. Firstly, an updated methodology for creating 30-m cropland structure information was provided inchapter 2 and exhibited high accuracy. Secondly, different agricultural systems (i.e., stateand private farms) in cold region of China significantly affected cropland structure patternsthrough rice paddy expansion. Thirdly, a positive effect on the grain safety was observedfrom the conversion of upland crops to paddy field, accompanied by different cropevolutions in state and private farms. Finally, the cooling effect of rice paddy was quantifiedin cold region of China. |
| Subject Area | 地图学与地理信息系统 |
| Language | 中文 |
| Document Type | 学位论文 |
| Identifier | http://ir.xjlas.org/handle/365004/15441 |
| Collection | 中国科学院新疆生态与地理研究所 研究系统 |
| Affiliation | 中国科学院新疆生态与地理研究所 |
| First Author Affilication | 中国科学院新疆生态与地理研究所 |
| Recommended Citation GB/T 7714 | 潘涛. 三江平原耕地结构演化及其对粮食产量和地表热环境的影响研究[D]. 北京. 中国科学院大学,2020. |
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