Study of the Wind Conditions in the South China Sea and Its Adjacent Sea Area

An increasing number of marine structures have been built for coastal protection and marine development in recent years,and wind,which is crucial to marine structures,should be analyzed.Therefore,typhoon frequency,wind climate,wind energy assess-ment,and extreme wind speed in the South China Sea(SCS)are investigated in detail in this study.The data are obtained from the China Meteorological Administration,the European Centre for Medium-range Weather Forecasts,and the National Centers for Envi-ronmental Prediction.The offshore wind energy potential is analyzed at five sites near the coast.The spatial and monthly frequencies of tropical cyclones for different intensity categories are analyzed.The extreme wind speed is fitted by five distribution models,and the generalized extreme value(GEV)distribution is selected as the most suitable function according to the goodness of fit.The spa-tial distributions of extreme wind speeds in the SCS are plotted on the basis of the GEV distribution and ERA5 data sets.The influ-ences of the distribution models and data sets on the calculated results are discussed.Moreover,the monthly extreme wind speed and comparison with the results of previous studies are analyzed.This study provides a reference for the design of wind turbines.     

Impact of Surface Potential Vorticity Density Forcing over the Tibetan Plateau on the South China Extreme Precipitation in January 2008. Part Ⅱ:Numerical Simulation

The surface air convergence on the eastern flank of the Tibetan Plateau (TP) can increase the in situ surface potential vorticity density (PVD). Since the elevated TP intersects with the isentropic surfaces in the lower troposphere, the increased PVD on the eastern flank of TP thus forms a PVD forcing to the intersected isentropic surface in the boundary layer. The influence of surface PVD forcing over the TP on the extreme freezing rain/snow over South China in January 2008 is investigated by using numerical experiments based on the Finite-volume Atmospheric Model of the IAP/LASG (FAMIL). Compared with observations, the simulation results show that, by using a nudging method for assimilating observation data in the initial flow, this model can reasonably reproduce the distribution of precipitation, atmospheric circulation, and PVD propagation over and downstream of the TP during the extreme winter precipitation period. In order to investigate the impact of the increased surface PVD over the TP on the extreme precipitation in South China, a sensitivity experiment with surface PVD reduced over the TP region was performed. Compared with the control experiment, it is found that the precipitation in the TP downstream area, especially in Southeast China, is reduced. The rainband from Guangxi Region to Shandong Province has almost disappeared. In the lower troposphere, the increase of surface PVD over the TP region has generated an anomalous cyclonic circulation over southern China, which plays an important role in increasing southerly wind and the water vapor transport in this area;it also increases the northward negative absolute vorticity advection. In the upper troposphere, the surface PVD generated in eastern TP propagates on isentropic surface along westerly wind and results in positive absolute vorticity advection in the downstream areas. Consequently, due to the development of both ascending motion and water vapor transport in the downstream place of the TP, extremely heavy precipitation occurs over southern China. Thereby, a new mechanism concerning the influence of the increased surface PVD over the eastern TP slopes on the extreme weather event occurring over southern China is revealed.     

极限学习机模型在季冻区深基坑地表沉降预测中的应用

针对传统数据驱动模型存在收敛速度慢、过度拟合等问题,提出了基于极限学习机算法的基坑地表沉降预测方法。结合季冻区地铁车站基坑的特点,提取基坑开挖时间、开挖深度、围护桩顶位移、围护桩内力、支撑轴力及地表温度等特征信息,建立极限学习机回归预测模型,选用实例数据进行算例分析,并将其与传统回归预测模型进行对比,实验结果表明,极限学习机模型收敛速度快,泛化能力强,其预测精度优于传统预测模型,且在学习速度方面优势明显,对深基坑安全监控有一定的实用价值。     

单基站CORS系统在池州市“数字城市”像控点测量中的应用

重点介绍了单基站CORS系统在池州市"数字城市"像控点测量中的应用,同时对单基站CORS系统的建立、作业流程以及质量控制进行了简要阐述。     

基于LiDAR点云数据的可视域计算研究

当前GIS软件中通视分析建立在DEM数据基础上,而DEM中不含植被和建筑物信息,从而会造成通视分析误差。通过Li DAR点云数据获取高精度植被和建筑物高度,提出一种顾及地物的插值算法,生成同一网格大小的DEM与DSM,在其上分别进行通视域分析,并将分析结果进行对比,发现DEM比DSM更容易扩大视域范围,从而产生了分析误差,验证了利用DSM进行通视分析的可行性。     

地理国情普查的技术流程及作业方法

第一次全国地理国情普查是一项重大的国情国力调查,根据一年多从事地理国情生产的工作经验,并结合生产的实际情况,本文介绍了地理国情普查的技术流程及作业方法,总结了生产中的注意事项及作业经验,希望能够为地理国情普查的生产和作业提供参考和借鉴。     

Wind wave characteristics and engineering environment of the South China Sea

Wave simulation was conducted for the period 1976 to 2005 in the South China Sea (SCS) using the wave model, WAVEWATCH-III. Wave characteristics and engineering environment were studied in the region. The wind input data are from the objective reanalysis wind datasets, which assimilate meteorological data from several sources. Comparisons of significant wave heights between simulation and TOPEX/Poseidon altimeter and buoy data show a good agreement in general. By statistical analysis, the wave characteristics, such as significant wave heights, dominant wave directions, and their seasonal variations, were discussed. The largest significant wave heights are found in winter and the smallest in spring. The annual mean dominant wave direction is northeast (NE) along the southwest (SW)-NE axis, east northeast in the northwest (NW) part of SCS, and north northeast in the southeast (SE) part of SCS. The joint distributions of wave heights and wave periods (directions) were studied. The results show a single peak pattern for joint significant wave heights and periods, and a double peak pattern for joint significant wave heights and mean directions. Furthermore, the main wave extreme parameters and directional extreme values, particularly for the 100-year return period, were also investigated. The main extreme values of significant wave heights are larger in the northern part of SCS than in the southern part, with the maximum value occurring to the southeast of Hainan Island. The direction of large directional extreme H _s values is focus in E in the northern and middle sea areas of SCS, while the direction of those is focus in N in the southeast sea areas of SCS.     

The behaviour of beach elevation contours in response to different wave energy environments

Within the context of a warming climate, there are wide and increasing concerns about the way beaches respond to different wave energy environments. However, behavioural differences in changes in beach elevation contours (including shorelines) in different wave energy environments remain unknown. Thus, it is unilateral to evaluate the changes in beaches based on a single elevation contour (e.g. shoreline) in coastal engineering and management applications. In this study, based on the collected shoreline and wave energy data of two international beaches, as well as the measured beach elevation contour data from Yintan Beach and the corresponding wave energy data simulated by Xbeach, our results show that frequency distributions of beach elevation contour changes exhibit distinct features under different wave energy environments. Under high wave energy environments, the frequency distributions of beach elevation contour changes show a Gaussian distribution. However, frequency distributions of beach elevation contour changes present a power law, intermediate between the logarithmic and Gaussian distributions under low and moderate wave energy environments, respectively. Furthermore, the conceptual model of beach elevation contour changes constructed by this study indicates that the relative importance of the wave energy and sediment resistance determines this phenomenon. © 2020 John Wiley & Sons Ltd     

Scientists' warning on extreme wildfire risks to water supply

2020 is the year of wildfire records. California experienced its three largest fires early in its fire season. The Pantanal, the largest wetland on the planet, burned over 20% of its surface. More than 18 million hectares of forest and bushland burned during the 2019–2020 fire season in Australia, killing 33 people, destroying nearly 2500 homes, and endangering many endemic species. The direct cost of damages is being counted in dozens of billion dollars, but the indirect costs on water-related ecosystem services and benefits could be equally expensive, with impacts lasting for decades. In Australia, the extreme precipitation (“200 mm day −1 in several location”) that interrupted the catastrophic wildfire season triggered a series of watershed effects from headwaters to areas downstream. The increased runoff and erosion from burned areas disrupted water supplies in several locations. These post-fire watershed hazards via source water contamination, flash floods, and mudslides can represent substantial, systemic long-term risks to drinking water production, aquatic life, and socio-economic activity. Scenarios similar to the recent event in Australia are now predicted to unfold in the Western USA. This is a new reality that societies will have to live with as uncharted fire activity, water crises, and widespread human footprint collide all-around of the world. Therefore, we advocate for a more proactive approach to wildfire-watershed risk governance in an effort to advance and protect water security. We also argue that there is no easy solution to reducing this risk and that investments in both green (i.e., natural) and grey (i.e., built) infrastructure will be necessary. Further, we propose strategies to combine modern data analytics with existing tools for use by water and land managers worldwide to leverage several decades worth of data and knowledge on post-fire hydrology.     

DIE TECHNISCHE UND WIRTSCHAFTLICHE BEDEUTUNG DER GLETSCHER / The Role of Glaciers in the Economy and Technical Development of Alpine Countries

English Summary

In former times the inhabitants of alpine regions looked upon glaciers as an uncanny and dangerous realm which they avoided as far as possible. It was only around the middle of the 18th Century that man became gradually aware of the beauty of the mountains, and approximately at the same time science started to take an interest in glaciers. Most of the questions raised in this field have been solved since. However, even in our times it is not sufficiently well known that glaciers, which are responsible for the characteristics of the regime of alpine rivers, are interesting not only from the point of view of physical geography, but are also of great importance for the economy and technical development of alpine countries.

Torrents which are fed by the melted ice, carry great quantities of water at periods when other streams frequently run dry. Nevertheless, in the terms of hydraulic power economy, it would be an over simplification to consider glaciers as reservoirs. It must not be forgotten, that in the Alps precipitation is highest during the summer months, and consequently that rivers carry more water during that season than during any other period of the year. The presence of glaciers adds to the extreme situation, and therefore the equalisation of seasonal differences in the runoff of glaciers necessary for power economy requires more storage capacity than is needed for catchment areas without glaciers.

On the other hand, there are also arid zones in the Alps, where conditions are entirely different. I am thinking of the deep valleys, running east to west, which are screened from rain by high mountain ranges, as for instance in the Wallis, the Vintschgau, parts of Western Tyrol and the Engadine. In these valleys it is particularly the slopes open to the south and exposed to constant insolation which show the typical characteristics and vegetation of arid zones. Precipitation during the growing season is often far less than the 600mm which is considered as the minimum needed for most types of cultivation, so much so that artificial irrigation has been practised for many generations. Whenever possible, the aqueducts, often very primitive, are fed by the glacier runoff of the large mountain massifs which never run dry. In some parts of the Wallis and in the South and West Tyrol, the water had to be conducted long distances and across difficult terrain; the construction of these primitive aqueducts was therefore a truly difficult task, as financial and technical resources available for that purpose were very inadequate.

This additional water-supply produced by glaciers in summer has a very definite effect on the large rivers rising in the Alps and flowing down in all directions, to name a few of them, the Rhine, the Inn, the Drave, the Rhône, the Adige etc. Not a single one of them has a low water level record in summer equal to that of the Weser or the Elbe and many other rivers of Central Europe which are not fed by glaciers. This low water level in summer has naturally a very detrimental effect on the navigation of rivers, and also on their capacity to replenish ground-water resources. The abundance of glacier runoff assures a fairly steady supply of water to the first mentioned rivers even in their lower courses, a fact which is of special importance for hydraulic economy in general and for hydraulic energy economy in particular. The rich potential of hydraulic energy in Jugoslavia, for instance, suffers from the fact that the quantity of water carried by the karst-rivers is considerably smaller in summer than it is in winter. The river Drave with its tributaries fed by glacier runoff from the Alps in Carynthia and East Tyrol, is practically the only river in Jugoslavia used to a considerable extent for the production of hydraulic power. It carries even more water in summer than during other seasons. This river, which serves to equalise the seasonal production of energy is therefore most valuable for the power economy of the country.

Short-term changes in the size of glaciers which are the subject of our present symposium, are causing the development of glacier lakes of which there exist several types. Most dangerous are those in larger valleys, caused by the tongue of a side glacier forming a dam, for instance here in the Ötztal Alps, at the Gurgler and at the Rofener Eissee near Vent. Other lakes develop in the basins left behind by the tongues of former glaciers. Water suddenly released from glacier lakes due to a breach of the ice or moraine dam, has frequently been the cause of terrible catastrophes. Attempts have therefore been made to protect the valleys against floods by the construction of flood reservoirs suitably situated below the glacier. An example of this type is the reservoir dam which the Austrian torrent-control authorities constructed in the Martellvalley (South Tyrol) in 1898/99 to prevent damage from an eventual breach in the banks of a glacier lake which had developed. Nowadays the large reservoirs constructed for hydro-electric power provide even greater protection.

Reservoirs for power plants in the Alps, which are created by the construction of large dams, require the existence of basins hollowed out by former glaciers during a long geological period. Outside of the glaciated areas, such basins can generally be created only by artificially blocking up a river-valley. This type of reservoir can be easily distinguished from that described above by its entirely different outline.

It must finally be remembered that the large load of sediment carried by glacial rivers has its economic and technical problems. Although it will probably take centuries to fill up the largest hydro-electric reservoirs, or even to considerably reduce their storage capacity, there are many smaller lakes in which this development will take no more than decades. Deposits of mud, for instance in the reservoir of the Margaritze, in the “Tauernfraftwerke” area had, after a mere decade accumulated to the extent that the power-plant administration had to install a floating suction dredger to remove at least part of the sediment. In this connection it was, however, important not to overload the river downstream with mud to such a degree as to cause damage to the fish population. Careful observation was needed to find out to what extent the river was able to cope with the artificial inflow of mud, and to follow the dispersion of the peak values of the suspesion load.

Nowadays waters destined for the generation of hydro-electric power are collected at the highest possible altitudes. An interesting example of the application of modern methods of this type is the collection of the runoff from beneath the Brandner Ferner in the Silvretta from where it is conveyed to the Lünersee. As a water intake on the surface was impossible due to the difficult terrain, a tunnel had to be driven through the rock bed of the glacier and there, immediately underneath it, in an ice cave, the water flows into a cage consisting of strong steel girders. This cage retains the large bolders, while the water from the bottom of the glacier runs off into the tunnel.