Changes in reference evapotranspiration over China during 1960–2012: Attributions and relationships with atmospheric circulation          下载免费PDF全文

Rongfan Chai  Shanlei Sun  Haishan Chen  Shujia Zhou 《水文研究》2018,32(19):3032-3048

This study investigates reference evapotranspiration (ET₀) trends in China from 1960 to 2012 based on the Penman–Monteith equation and gridded meteorological measurements. Under the combined impacts of factors influencing ET₀ (i.e., net radiation [RN], mean temperature [TAVE], vapour pressure deficit [VPD], and wind speed [WND]), both seasonal and annual ET₀ for the whole China and more than half of the grids decreased over the past 53 years. The attribution analyses suggest that for the whole China, the WND is responsible for annual and seasonal ET₀ decreases (excluding summer, where RN is responsible). Across China, the annual cause of WND with the largest spatial extent (43.1% of grids) mainly derives from north of the Changjiang River Basin (CJRB), whereas VPD (RN) as a cause is dispersedly distributed (within and to the south of the CJRB). In summer, RN is dominant in more than half of the grids, but the dominance of VPD and WND accounts for approximately 90% of grids during the remaining seasons. Finally, the correlation coefficients between ET₀ and the Atlantic Oscillation (AO), North AO, Indian Ocean Dipole (IOD), Pacific Decadal Oscillation (PDO), and El Niño Southern Oscillation (ENSO) indices with different lead times are calculated. For the whole China, annual and seasonal ET₀ always significantly correlate with these indices (excluding the IOD) but with varied lead times. Additionally, near half of the grids show significant and maximum (i.e., the largest one between ET₀ and a certain index with a lead time of 0–3 seasons) correlation coefficients of ET₀ with PDO in spring and summer, ENSO in autumn, and AO in winter. This study is not only significant for understanding ET₀ changes, but it also provides preliminary and fundamental reference information for ET₀ prediction.  相似文献   

Width variations control the development of grain structuring in steep step-pool dominated streams: insight from flume experiments     

Matteo Saletti  Marwan A. Hassan 《地球表面变化过程与地形》2020,45(6):1430-1440

We report results from flume experiments designed to study the effect of width variations on the formation and stability of steps in steep streams. To physically model channel width changes we inserted multiple trapezoidal elements in the flume. Two competing effects are in play: a fluidic effect, suggesting that steps are more likely to form in wide areas because of deposition enhanced by lower shear stress, and a granular effect, suggesting that steps are more likely to form in narrow areas because of particle jamming. Our experiments show that width variations enhance the formation of steps. Although steps can form in every location, those in narrow/narrowing areas are more common, more stable and they occupy a larger portion of the channel width. These results stress the importance of particle interactions in coarse-bedded streams and help river engineers by providing a new element to consider when designing step-pool sequences in river restoration projects. © 2020 John Wiley & Sons, Ltd.  相似文献   

潍坊市耕地资源动态变化及驱动力分析   总被引：1，自引：0，他引：1  

石文华  高岚 《山东国土资源》2009,25(6):35-38

潍坊市是国家重要的农副产品生产基地。近几年来，随着经济的发展，耕地资源迅速退化和流失，使得人口与耕地的矛盾日渐突出。通过对相关数据的分析，揭示了潍坊市自改革开放以来耕地资源的变化趋势。运用定性和定量的方法对耕地数量变化的驱动因子进行了分析；并结合潍坊市耕地资源利用的具体情况，提出保护耕地的对策与建议。  相似文献   

“一带一路”沿线国家1992年—2015年土地覆盖变化的时空格局及其驱动力分析          下载免费PDF全文

海凯  王思远  涂平  杨瑞霞  马元旭  梁娟珠  刘卫华  吴林霖 《遥感学报》2022,26(6):1220-1235

土地覆盖变化影响局域的能源和水平衡，并在全球范围内促进碳的净排放。基于欧空局气候变化倡议项目最新发布的1992年—2015年300 m分辨率的全球土地覆盖数据集，本文分析了1992年—2015年“一带一路”沿线主要土地覆盖类型变化的时空特征及其驱动力。研究结果表明：1992年—2015年沿线耕地、草地和建设用地面积分别增加190.00×10³ km²、57.97×10³ km²和260.39×10³ km²，森林、灌木、湿地和水体面积分别减少61.14×10³ km²、34.22×10³ km²、74.28×10³ km²和44.41×10³ km²。2000年—2015年与1992年—2000年相比，沿线土地覆盖变化的区域空间格局基本一致，但区域变化呈现了新的特征。东南亚区建设用地扩张明显加速，耕地面积增速下降，森林面积减速上升，灌木面积减速下降明显；东亚区建设用地持续高速扩张，耕地面积持续减少，森林面积减速明显下降，草地面积持续增加；中东欧区建设用地扩张速度明显下降，耕地面积减速上升；俄罗斯建设用地扩张持续缓慢，森林面积稳中有升，草地和灌木面积增速下降。分析进一步显示人口增长、气候变化、社会经济发展和政府相关政策是造成沿线国家土地覆盖变化的主要驱动因素。  相似文献   

海上风力发电机三桩基础波流力的计算     

陈志强  陈兵  康海贵  邵学 《海洋技术学报》2009,28(1)

考虑了波浪在水流中的变形,计算了波流共存场中海上风力发电机三柱基础的受力.应用离散涡法,求解了不可压缩粘性流体的水平二维涡量-流函数Navier-Stokes方程,模拟了不同桩位布置对波流场的影响.以及各桩受力和三桩基础总力的随布置方式不同的变化.  相似文献