Changes in air pollutants during the COVID-19 lockdown in Beijing:Insights from a machine-learning technique and implications for future control policy          下载免费PDF全文

Jiabao Hu  Yuepeng Pan  Yuexin He  Xiyuan Chi  Qianqian Zhang  Tao Song  Weishou Shen 《大气和海洋科学快报》2021,14(4):63-69

基于2015-2020年北京35个环境空气站和20个气象站观测资料,应用机器学习方法(随机森林算法)分离了气象条件和源排放对大气污染物浓度的影响.结果发现,为应对疫情采取的隔离措施使北京2020年春节期间大气污染物浓度降低了35.1％-51.8％;其中,背景站氮氧化物和一氧化碳浓度的降幅最大,超过了以往报道较多的交通站点.同时,2020年春节期间的气象条件不利于污染物扩散,导致多次霾污染事件发生.为进一步改善北京空气质量,未来需要优化减排策略.  相似文献   

Landsat-8 vs. Sentinel-2: examining the added value of sentinel-2’s red-edge bands to land-use and land-cover mapping in Burkina Faso     

Gerald Forkuor  Kangbeni Dimobe  Idriss Serme  Jerome Ebagnerin Tondoh 《地理信息系统科学与遥感》2018,55(3):331-354

The availability of freely available moderate-to-high spatial resolution (10–30 m) satellite imagery received a major boost with the recent launch of the Sentinel-2 sensor by the European Space Agency. Together with Landsat, these sensors provide the scientific community with a wide range of spatial, spectral, and temporal properties. This study compared and explored the synergistic use of Landsat-8 and Sentinel-2 data in mapping land use and land cover (LULC) in rural Burkina Faso. Specifically, contribution of the red-edge bands of Sentinel-2 in improving LULC mapping was examined. Three machine-learning algorithms – random forest, stochastic gradient boosting, and support vector machines – were employed to classify different data configurations. Classification of all Sentinel-2 bands as well as Sentinel-2 bands common to Landsat-8 produced an overall accuracy, that is 5% and 4% better than Landsat-8. The combination of Landsat-8 and Sentinel-2 red-edge bands resulted in a 4% accuracy improvement over that of Landsat-8. It was found that classification of the Sentinel-2 red-edge bands alone produced better and comparable results to Landsat-8 and the other Sentinel-2 bands, respectively. Results of this study demonstrate the added value of the Sentinel-2 red-edge bands and encourage multi-sensoral approaches to LULC mapping in West Africa.  相似文献   

西昌市1989—2018年林地草地湿地动态变化特征分析     

张景华  欧阳渊  刘洪  张腾蛟  李富  黄勇 《中国地质调查》2021,8(6):135-143

遥感技术已被广泛应用于生态环境调查与研究。为获取西昌市近30 a生态环境演化趋势,利用1989年、2000年、2010年的专题绘图仪(Thematic Mapper,TM)遥感影像和2018年的陆地成像仪(Operational Land Imager,OLI)遥感影像,通过图像处理、目视解译和野外验证等方法,获得了西昌市1989—2018年的土地利用/覆盖数据,并对林地、草地和湿地的动态变化特征进行了研究。结果表明: 1989—2018年,西昌市林地、湿地和草地面积持续增加,生态环境持续向好; 林地主要分布于安宁河谷和邛海盆地四周山地,在牦牛山、螺髻山一带形成主要林区; 草地主要呈星岛状分布于牦牛山、螺髻山一带林地之间; 湿地以河流湿地与湖泊湿地为主,主要沿安宁河及邛海分布。但仍存在一些问题: 森林存在针叶化现象较普遍、树种单一等问题,需要重点加强林区火灾防范; 草地多数呈零星片状分布,不具有完整的系统结构和良好的功能,多数草地承载力和生产力较低,不宜大规模开发利用,应通过封山育林促使其向森林转化; 湿地分布也比较局限,需要着力予以保护。研究成果可为西昌市生态保护修复措施的制定及经济社会可持续发展提供科学依据。  相似文献   

海南岛天然橡胶林台风灾害风险评价   总被引：1，自引：0，他引：1  

黄海静  杨再强  王春乙  张京红  张亚杰  张明洁 《气象与环境学报》2019,35(5):130-136

台风灾害是海南橡胶种植中影响最为严重和主要的灾害,为对其风险进行定量评估,本研究以海南岛天然橡胶林为研究对象,基于灾害风险评估理论,融合橡胶台风灾害、社会经济和气象数据,建立橡胶台风灾害危险性、暴露性和脆弱性评价模型,利用加权综合评价法开展天然橡胶林台风灾害风险评价。结果表明：海南橡胶种植高风险区位于沿海台风发生频繁市县,其中琼海、文昌、海口为海南岛橡胶灾害风险最高的地区,其次陵水、万宁、琼中、屯昌、东方等地区灾害风险也较高。风险最低地区位于中部五指山、保亭、乐东、三亚等地区,评价结果与实际灾害发生以及种植情况相符。评价结果表明,台风灾害危险性是风险的主导因子,但非单一决定因子,种植技术、品种改良等措施对脆弱性降低起到了较好的促进作用。评价结果可为橡胶林避灾防灾及种植布局提供依据。  相似文献   

基于WRF模式的风电场短期风速集成预报方法研究     

叶小岭  支兴亮  邓华 《气象》2019,45(1):88-98

风能始源于大气的运动,具有很大的随机性和间歇性。风速预测是风电场风功率预测的基础,其准确性具有重要的意义。对于复杂地形条件下,风速的预报一直是各国研究的难点和重点。为了提高风电场短期风速预报的准确性,本研究采用多种边界层参数化方案来集成预报风速,将各单一边界层参数化方案预报的风速及相应的实测风速数据,应用随机森林算法建立集成预报模型,对风电场的短期风速进行集成预报研究。试验结果表明,采用集成预报风速方法,预报的风速误差相比于单一边界层参数化方案预报的风速误差明显减小,对研究区域的风速、风向等气象要素有着较好的模拟效果,能够有效提高风速预报的准确率。  相似文献   

A simple model to estimate monthly forest evapotranspiration in Japan from monthly temperature     

Hikaru Komatsu  Tomonori Kume  Kyoichi Otsuki 《水文研究》2010,24(13):1896-1911

The estimation of evapotranspiration (E) in forested areas is required for various practical purposes (e.g. evaluation of drought risks) in Japan. This study developed a model that estimates monthly forest E in Japan with the input of monthly temperature (T). The model is based on the assumptions that E equals the equilibrium evaporation rate (E_eq) and that E_eq is approximated by a function of T. The model formulates E as E (mm month⁻¹) = 3·48 T ( °C) + 32·3. The accuracy of the model was examined using monthly E data derived using short‐term water balance (WB) and micrometeorological (M) methods for 15 forest sites in Japan. The model estimated monthly E more accurately than did the Thornthwaite and Hamon equations according to regression analysis of the estimated E and E derived using the WB and M methods. Although the model tended to overestimate monthly E, the overestimation could be reduced by considering the effect of precipitation on E. As T data are commonly available all over Japan, the model would be a useful tool to estimate forest E in Japan. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Analysis of the contributions of topographic,soil, and vegetation features on the spatial distributions of surface soil moisture in a steep natural forested headwater catchment          下载免费PDF全文

Wei‐Li Liang  Sheng‐Lun Li  Feng‐Xu Hung 《水文研究》2017,31(22):3796-3809

Surface soil moisture has been extensively studied for various land uses and landforms. Although many studies have reported potential factors that control surface soil moisture over space or time, the findings have not always been consistent, indicating a need for identification of the main factors. This study focused on the static controls of topographic, soil, and vegetation features on surface soil moisture in a steep natural forested headwater catchment consisting of three hillslope units of a gully area, side slope, and valley‐head slope. Using a simple correlation analysis to investigate the effects of the static factors on surface soil moisture at depths of 0–20 cm at 470 points in 13 surveys, we addressed the characteristics of surface soil moisture and its main controlling factors. The results indicated that the mean of surface soil moisture was in the decreasing order of gully area > valley‐head slope > side slope. The relationship between the mean and standard deviation of surface soil moisture showed a convex‐upward shape in the headwater catchment, a negative curvilinear shape in the gully area, and positive curvilinear shapes at the side and valley‐head slopes. At the headwater catchment and valley‐head slope, positive contributions of soil porosity and negative contributions of slope gradient and saturated hydraulic conductivity were the main controlling factors of surface soil moisture under wetter conditions, whereas positive contributions of topographic wetness index and negative contributions of vegetation density were the main controlling factors of surface soil moisture under drier conditions. At the side slope underlain by fractured bedrocks, only saturated hydraulic conductivity and vegetation density were observed to be the controlling factors. Surface soil moisture in the gully area was mainly affected by runoff rather than were static features. Thus, using hillslope units is effective for approximately estimating the hydrological behaviours of surface moisture on a larger scale, whereas dependency between the main static factors and moisture conditions is helpful for estimating the spatial distributions of surface moisture on a smaller scale.  相似文献   

Holocene river and slope activity in the Visoko Basin,Bosnia‐Herzegovina – climate and land‐use effects     

S. DREIBRODT  C. LUBOS  R. HOFMANN  N. MÜLLER‐SCHEEßEL  I. RICHLING  O. NELLE  M. FUCHS  K. RASSMANN  Z. KUJUNDŽIĆ‐VEJZAGIĆ  H.‐R. BORK  J. MÜLLER 《第四纪科学杂志》2013,28(6):559-570

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Suspended sediment transport regime in a debris‐flow gully on Vancouver Island,British Columbia     

Craig J. Nistor  Michael Church 《水文研究》2005,19(4):861-885

In debris‐flow‐prone channels, normal fluvial sediment transport occurs (nearly exclusively in suspended mode) between episodic debris‐flow events. Observations of suspended sediment transport through a winter season in a steepland gully in logged terrain revealed two event types. When flows exceeded a threshold of 270 l s⁻¹, events yielded significant quantities of sediment and suspended sediment concentration increased with flow. Smaller events were strongly ‘supply limited’; sediment concentration decreased as flow increased. Overall, there is no consistent correlation between runoff and sediment yield. Within the season, three subseasons were identified (demarcated by periods of freezing weather) within which a pattern of fine sediment replenishment and evacuation occurred. Finally, a signature of fine sediment mobilization and exhaustion was observed within individual events. Fine sediment transport occurred in discrete pulses within storm periods, most of the yield occurring within 5 to 15% of storm runoff duration, so that it is unlikely that scheduled sampling programs would identify significant transport. Significant events are, however, generally forecastable on the basis of regional heavy rainfall warnings, providing a basis for targeted observations. Radiative snowmelt events and rain‐on‐snow remain difficult to forecast, since the projection of temperatures from the nearest regular weather station yields variable results. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

Effects of commercial timber harvesting on streamflow regimes in the Plynlimon catchments,mid‐Wales     

M. Robinson  A. Dupeyrat 《水文研究》2005,19(6):1213-1226

This paper presents the first large‐scale British study of the impacts of commercial forest cutting on stream‐flow regimes. The 70% forested headwaters of the River Severn are part of the intensively instrumented long‐term Plynlimon catchment study into the impact of land use on stream flow. The forest area, comprising predominantly Sitka spruce (Picea sitchensis), was planted mainly in the 1930s and 1940s. Harvesting commenced in the mid‐1980s and over the study period about half the forest has been felled. Changes in annual water yield and extreme flows were studied in four nested catchments ranging in area from about 1 to 10 km² and compared with an adjacent benchmark grassland catchment. As expected from earlier process studies the cutting of the forest increased total annual flows. Less expected was the clear evidence that the felling augmented low flows. This informs a long‐standing debate whether upland forestry increases or reduces baseflows. A particularly notable result was the lack of impact of the harvesting on storm peak flows. This may result from the application of forest management guidelines designed to reduce soil damage and erosion during the harvesting, and indicates that the forest itself has a limited impact on flooding. These findings are timely because British forest expansion peaked in the 30 years following the Second World War, and large areas of these woodlands are now approaching economic maturity and will be harvested in the next two decades. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献