Spatio-temporal evolution and topographic gradient effect of land use and ecosystem service value in the Lhasa River Basin

The Lhasa River Basin forms an essential human settlement area in the southern part of the Qinghai-Tibet Plateau.This study employed ecosystem service value(ESV)evaluation model,terrain gradient grading,and Geodetector to analyze land use and ESV in the Lhasa River Basin from 1985 to 2020.The findings reveal that:(1)From 1985 to 2020,grassland was the dominant land use.There was a trend of grassland reduction and the expansion of other land types.(2)ESV has increased over the research period(with a total increase of 0.84%),with higher values in the southeast and lower values in the northwest.Grassland contributed the most to ESV,and climate regulation and hydrological regulation were the ecosystem services that contribute the most to ESV.(3)Natural factors like NDVI and altitude,as well as economic factors like population density and distance from roads,influenced the spatial differentiation of ESV,the explanatory power of NDVI reached up to 0.47.The interaction between factors had a greater impact than individual factors.These research results can provide theoretical support for national spatial planning and ecological environment protection in the Lhasa River Basin and other similar areas.

Spatiotemporal evolution of ecosystem service value and topographic gradient effect in the Da-Xiao Liangshan Mountains in Sichuan Province,China

The Da-Xiao Liangshan mountains are critical ecological function areas and essential ecological barriers in the upper reaches of the Yangtze River in China.This study selected a total of six periods of land use land cover(LULC)data from 1995 to 2020,to estimate the ecosystem service value(ESV)and analyzed its spatiotemporal evolution and topographic gradient divergence.The results showed that:(1)The ESV increased by 1.1 billion yuan,with an increase rate of 1.47%from 1995 to 2020.Two time periods,2005–2010 and 2015–2020,showed more significant increases than other periods.(2)The elevation and slope of mountainous areas determine the type of land use and further influence the spatial pattern of ESV.(3)Although woodland and grassland are the main land use types of the study area(more than 90%),the hydrological regulation function of the water area partially compensated for the impact of the encroachment of the built-up area on the ESV of grassland.(4)The spatial distribution of ESVs showed an inverted V-shaped characteristic as the topographic gradient increased,with the dominant position being the 5th topographic gradient zone.Finally,this study provided relevant recommendations for ecosystem protection and optimization.The findings of this study clarified the influence of topographical factors on the spatial differentiation of ESV and provided novel insights into ecosystem protection.

NUMERICAL SIMULATION STUDY OF THE EFFECTS OF TERRAINAROUND TAIWAN ON TYPHOON DOT (1990)

With the use of analyzed TCM-90 data,Typhoon Dot (1990)and complex evolutions are successfullyreproduced in numerical sboulation as it travels over the island of Taiwan. The simulation includes theformation of secondary highs in both circulation and geopotential fields, trajectory jumps during mer-gence with main centers, anomalous northward movement of a low center west of Taiwan, evolutionalprocess of a low-level jet over the Taiwan Straits and significant deviations of circulation center fromgeopotentia1 center between upper and lower levels. By examining ev0lutions of 3-h interval simulatedresults, detailed processes of changes in structure and track before and after Dot’s passage of Taiwanis given, whose evolutional images are otherwise impossible with conventionai observations at intervalsof 6 h. A number of control experboents are conducted in the end of the work for understanding causesand mechanisms behind various properties.

On the Determination and Characteristics of Effective Roughness Length for Heterogeneous Terrain

A new method is proposed for the effective roughness length (ERL) in heterogeneous terrain based on the principle of equalisation of momentum or heat fluxes calculated by the drag coefficient parameterization scheme used in the ECMWF numerical model. Compared with the area-weighted logarithmically averaged ERL (drag coefficient), the newly calculated ERL (drag coefficient) is about 40% (16%) larger with a roughness step of 2.3. These differences reach their maximum values when the ratio of smooth to rough surface is 60% to 40%. Since the determination by this method is not sensitive to the atmospheric stratification, it is suitable for use in climate models.

Refinement and Quantification of Terrain-Induced Effects on Global Gravity Data

The geodetic and geophysical applications of Earth Gravity Field parameters computed from Global Geopotential Models (GGMs) are quite on the increase despite the inherent commission and omission errors of these models. In view of this, this study focuses on refining and quantifying terrain-induced effects on Bouguer gravity anomalies computed directly from a total of seven recent GGMs. In the study, the Residual Terrain Model (RTM) technique was used to estimate the residual terrain effects that were added to the GGM-computed Bouguer gravity anomalies at the sixty test points in Enugu State, Nigeria. The computed residual terrain effects range from -24.6 to 37.5 mgal while the percentage of the omission errors of the GGMs based on their Root-Mean-Square (RMS) differences ranges from 7.8% to 44.7%. It can be concluded that GGM-refined Bouguer gravity anomalies are better in accuracy than the unrefined GGM-computed Bouguer gravity anomalies and hence there is need for accurate height information in the development of GGMs. We, therefore, recommend that refined Bouguer gravity anomalies obtained from HUST-Grace2016s, EIGEN-6C4 and GECO that gave best improvement amongst the seven GGMs under consideration should be used to supplement the available terrestrial Bouguer anomalies for geodetic and geophysical applications within the study area.

Effect of the Real Irregular Terrain on the Lightning-radiated Electromagnetic Field Propagation

The propagation of the lightning-radiated electromagnetic field along the real irregular terrain around Yangzhou Direction Finder(DF)site(119°42′E,32°39′N)and Nanjing DF site(118°46′E,32°03′N)of Jiangsu Province in China is estimated.The results show that the rough irregular terrain results in the rapid magnitude attenuation and the increase of the rise-time of the field waveform.For example,for the Yangzhou DF site as the circumference of a radius of 45 km,the root-mean-squared height(RMSH)of the real irregular terrain varies from 7 to 33 m;the extra field attenuation relative to the ideal ground surface ranges from 1%to 11%,and the extra rise-time increment varies from 0.1 to 0.6μs.Therefore,the extracted current peak of lightning return stroke may be underestimated from the remotely measured electromagnetic field,and the error varies along with different azimuths.

Analysis of the Adjacent Terrain Effect on the Properties of Ground Motion

The explicit finite element analysis method combined with the artificial transmitting boundary theory is performed to evaluate the adjacent terrain effects on ground motion,and the influence of the distance between adjacent terrains on the topographical amplification effects on ground motion is studied. The results show that:( 1) Compared to the case of a single hill,the presence of adjacent hills has little effect on the shape of the spectral ratio curve,but has a significant effect on the value of spectral ratio,which is dependent on the locations of observation points.( 2) The presence of adjacent hills has a greater effect on high-frequency ground motion,and with the increase of the distance between adjacent hills,such an effect weakens gradually,and the effect of the composite topography combined with multiple hills on ground motion gradually approaches that of a single hill.

Numerical simulation of mean interference effects for the interfering buildings with different heights

The mean wind-induced interference effects between two high-rise buildings,in which the interfering buildings have different heights,were numerical simulated in the terrain roughness of B and D types by the Reynolds stress equation model(RSM)of fluent.The results are in good agreement with those of the wind tunnel test.Influences of the relative arrangement of two buildings,the height of the interfering buildings and the terrain roughness upon the mean interference effects were analyzed,and the space distributions of IFCPs on the principal building under tandem arrangement were studied.The results indicate that the lower interfering buildings can always bring larger interference factors comparing to the higher ones under tandem arrangement except that the height is larger than 1.25h,and the heights' influence on the mean interference effects will increase as the reduced spacing of two buildings.The influence of heights will be little under stagger arrangement.

Numerical Prediction of Strong Wind Induced by Topographic Effect

This paper describes the numerical study of nonstratified airflow over a real complex terrain. Attention is focused on the mechanism of a local strong wind induced by a topographic effect. In order to clarify the mechanism of the occurrence of strong winds accompanied by the effects of terrain, the use of a numerical simulation is very effective, in which conditions can be set without the influence of ground roughness and temperature distribution. As a result, airflow converged to a small basin of mountain terrain in the upper stream, and local strong wind was generated leeward along the slope of the mountain terrain. Furthermore, the influence of the reproduction accuracy of geographical features, that is, horizontal grid resolution, was examined. Consequently, to reproduce the above-mentioned local strong wind, it was shown that horizontal grid resolution from 50 m to about 100 m was necessary.

Intensified haze formation and meteorological feedback by complex terrain in the North China Plain region

华北平原地区冬季雾霾污染频发,本研究结合地面观测,卫星反演和大气动力-化学耦合模拟发现,该地区复杂地形加剧了细颗粒物污染及其与大气边界层之间的相互作用.一方面,复杂地形导致污染在山麓平原积聚,加强迎风坡上升气流.在污染事件中,污染层易被抬升至1-2公里高度,高空较强的氧化能力利于二次气溶胶生成;另一方面,地形导致的污染层抬升和二次生成进一步加强气溶胶-边界层相互作用,削弱垂直扩散并加剧近地面大气污染.

2022年四川省复杂地形下持续性极端高温特征与模式误差分析

2022年8月四川省持续性极端高温天气过程范围广、强度大且持续时间长,全省有74.8%的站点打破近70年历史同期极值。本文选取四川地区2022年8月逐时2 m气温实况站点和历史同期数据,结合EC、CMA-GFS及CMA-MESO模式的2 m气温预报数据,分析了此次极端高温天气特征及预报误差。结果表明:(1)受地形影响,最高气温极值呈东高西低的分布特征;(2)受热岛效应影响,最高气温超历史极值较多的站点主要集中在盆地西部龙泉山脉附近;(3)3个代表站的最高气温平均值高、距平大、高温持续时间长,该时段的累计降水量明显低于历史同期平均值且降水日数显著偏少;(4)3个模式对于最低气温的预报准确率明显高于最高气温,而最优模式的高温预报准确率仅39.1%;(5)EC模式的预报优势主要在盆地低海拔站点,CMA-MESO模式在陡峭地形区域的预报效果要优于EC模式;(6)对于最高气温出现日期预报,EC模式在盆地和攀西地区效果更佳,CMA-GFS和CMA-MESO模式在川西高原效果更优。

河北保定市“23·7”强降水过程的观测特征分析

利用常规、加密观测资料,风廓线、双偏振雷达探测数据等,对2023年7月29日至8月2日发生在河北省保定市的强致灾性极端强降水过程的阶段性演变、观测特征等进行了分析,结果表明:1)在大陆高压与副高形成“北方高压坝”、台风“杜苏芮”减弱低压北上受阻的环流背景下,“杜苏芮”倒槽、“杜苏芮”残涡东侧的暖式切变线以及副高外围南风气流先后造成保定3个阶段的降水,最长单站降水持续时间70 h,7月30日07:00(北京时间,下同)至8月1日03:00涿州上游、海拔高度介于0.1~1 km的浅山区内不断出现短时强降水、“列车效应”显著,导致该区域出现极端的洪灾。2)29日倒槽降水雨带呈东北—西南向并随时间西北移,最大降水强度39.4 mm/h;30日副高西移,倒槽东侧位势梯度加大,同时台风“卡努”北侧东南气流并入,冀鲁地区低空东南急流加强、北伸,雨带呈“人”字形,降水落区无变化但短时强降水频次增大、强降水范围集中,雨强增至82.2 mm/h。3)切变线降水阶段,对流不稳定层增厚,降水主要集中在西南风—东南风切变线与南风—东风切变线之间,多局地短时强降水,最大雨强为76.3 mm/h。4)“杜苏芮”影响结束后,副高外围的低层偏南气流有明显的风速辐合,引发暖区局地降水,雨带呈准南北向且分为多轮次,各轮次降水落区次第向东移动且强度不断减小,阶段内最大降水强度54.2 mm/h。5)双偏振雷达图像显示,在倒槽降水阶段,前期为低质心暖云降水,对流发展高度最低,暖云碰并机制明显,雨滴粒子直径最大;“卡努”东南急流并入时段,0°C层下降、-10°C层抬升,对流高度增加,霰粒子增长、冰相粒子聚合融化,雨滴粒子浓度增至最大。在切变线降水时0~-10°C层厚度减小而-10~-20°C层厚度增加,对流发展高度最高,霰粒子凇附增长更为明显。6)地形对降水有增幅作用,倒槽降水阶段东南气流加强、北伸时与偏东风在保定中、北部辐合抬升,保定浅山区开始有山洪出现;“卡努”北侧东南风气流并入时的倒槽降水阶段以及切变线降水阶段,东南风与太行山北段近乎正交,保定西南部山区30日08:00至31日08:00出现24 h降水量极值。

凸出部放大效应在桥址高边坡地震稳定性评价中的应用探讨

深切峡谷区桥址高边坡凸出部具有三面临空和多面卸荷的典型地质地貌特征,研究边坡凸出部地震地形放大效应对桥址边坡安全控制尤为重要。依托特大桥桥址高边坡,研究了地震作用下边坡凸出部放大效应和变形破坏机制,优化了墩台位置。研究结果表明:(1)现场调查和数值模拟综合印证了边坡凸出部山顶碎屑流和主墩下部危岩体发育,受历史震害强。加速度随坡高呈现非线性放大的规律,开挖加剧了挖方区域加速度放大效应。凸出部(坡脊)坡腰和坡顶位置放大系数最大,加速度放大系数M_(PGA)最大可达3.2。(2)坡脊高频部分(5~12 Hz)的加速度傅里叶谱幅值普遍比坡谷大,开挖导致墩台上(下)边坡的傅里叶幅值的峰值减小在(增大)。开挖位置附近的傅里叶谱幅值的峰值均随峰值加速度的增加呈现先增大后减小的趋势。(3)《建筑抗震设计规范》中限制了最大坡高和放大系数极值,可能造成高边坡凸出部的动力放大效应被低估,使得凸出部地震稳定性评价结果偏危险。(4)为保证桥址边坡的地震稳定性,采用文中所述方法优化墩台外侧距坡面的距离为22~26 m。研究成果可为有凸出部的高边坡地震稳定性评价和墩台位置优化设计提供指导。

复杂地形区植被覆盖度遥感精细估算方法——以青藏高原山地区为例

植被覆盖度(FVC)是刻画地表植被覆盖的重要参数,是生态监测的重要指标。遥感已成为区域尺度FVC估算的主要技术手段,但受限于地形所导致的太阳辐射变化及遥感像元内部较强的异质性和复杂性,复杂地形区的FVC遥感估算精度仍有很大提升空间。研究利用随机森林回归模型,发展了一种综合遥感地表反射率、地形特征和观测几何信息的复杂地形区FVC遥感精细估算方法(SRTVG)。选择青藏高原祁连山区、黄河源区和横断山区为测试区,利用Sentinel-2影像对新方法进行了应用,并利用基于无人机影像获取的FVC数据和现有FVC遥感产品对新方法进行了评估。加入地形特征与观测几何信息后,新方法估算FVC的R2为0.89,均方根误差(RMSE)为0.13;相较于未加入地形特征与观测几何信息,新方法估算FVC的RMSE降低了19.26%—28.02%;相较于已有的MultiVI FVC产品和GEOV3 FVC产品,新方法估算FVC的RMSE分别降低了40.91%和16.67%。新发展的SRTVG方法提高了复杂地形区的植被覆盖度遥感估算精度,丰富了植被覆盖度遥感估算的技术方法体系。

秦岭东段洛河流域土地利用变化的地形梯度效应研究

明晰典型地势起伏区土地利用变化与地形因素的关系,对国土空间布局及区域协调发展具有重要现实意义。基于秦岭东段洛河流域多期土地利用数据及DEM数据,运用土地利用图谱法、标准差椭圆分析法和地形位分析法,揭示自2000年以来当地土地利用变化的时空分异特征,并探讨在不同土地利用变化下的地形梯度效应。研究结果表明:(1)20年间,土地利用变化多围绕耕地、草地和建设用地进行,且表现出显著的类型异质性及阶段差异性特点。(2)以耕地和林地为主的稳定型图谱面积占比达到88.17%,前期变化型和后期变化型分别为7.44%和3.51%,耕地被建设占用更偏向于无序化发展。(3)中低及其以上地形梯度的耕地逐渐趋向于低地形梯度区发展,林地的地形分布指数呈“S”型上升态势,草地则表现出中间高两边低的正态分布规律。(4)各图谱的地形分布指数随地形位增加表现出不同的趋势性规律,土地利用变化呈明显地形梯度效应。研究认为当地国土管理工作应重点关注反复变化型图谱和持续变化型图谱,并注意科学缓解和引导耕地水土流失及坡耕地开发利用问题。

基于InVEST模型的永安市生境质量时空演变及地形梯度效应研究

区域的可持续发展与其生境质量密切相关,其发展与提升对维持生态系统的平衡以及促进经济与社会的发展有着非常重要的意义。本研究以永安市为例,利用InVEST模型分析方法对2001-2021年生境质量进行评估并分析其时空演变特征,同时将生境质量与地形位指数梯度相结合,分析生境质量的地形梯度效应。结果表明:(1)永安市2001年、2011年以及2021年的平均生境质量指数分别为0.6354、0.6291、0.6285,总体生境水平较好,但呈下降的趋势。(2)生境质量在空间分布上存在明显的差异性,呈现研究区中间部分生境质量较差,随着研究区中部集中区域向外逐步扩大,生境质量逐步升高。(3)永安市生境质量分布指数具有明显的地形梯度效应,其平均生境质量随着地形位的升高而升高。

“三生空间”视角下陕西省1990—2020年土地利用转型及梯度效应

基于陕西省1990年、2000年、2010年、2020年土地利用数据,采用土地利用变化图谱、土地转移矩阵、地形位及分布指数等方法,分析“三生空间”用地转型过程及梯度分异特征,对全省国土空间优化、国土资源管理及耕地保护等具有重要意义。结果表明:(1)陕西省生产、生活用地主要分布在关中地区,生态用地主要分布在陕北地区和陕南山区。(2)1990—2020年土地利用转型较为剧烈,农业生产、其他生态用地面积净减少,工业生产、城镇和农村生活、林地生态、草地生态、水域生态用地面积净增加;变化剧烈程度呈现“陕北地区>关中地区>陕南山区”的空间分布特征。(3)随着地形位增加,主导地类由“农业生产用地”—“农业生产用地、草地生态用地”—“林地、草地生态用地”过渡;农业和工业生产用地、城镇和农村生活用地、水域生态用地面积占比逐渐减少,林地生态用地占比逐渐增加,草地、其他生态用地占比先增后减。

地形驱动下伊犁河谷草原生物灾害的分布效应

【目的】探究伊犁河谷草原生物灾害空间分布对地形因子的响应程度,为林草部门进行草原生物灾害防治工作与草原健康发展提供理论支持。【方法】结合实地调查技术与地理信息技术在地形的视角下对伊犁河谷草原鼠害、虫害、毒草害空间分布进行分析,并基于地理探测器分析地形对草原生物灾害的驱动机理。【结果】①伊犁河谷草原鼠害在海拔900~1200 m和1600~2100 m区间大面积分布;虫害主要集中在海拔800~1900 m区域内;毒草害在垂直空间上规律明显,主要集中在海拔1800~2500 m区域,随着海拔升高,毒草害面积增大,在海拔2000~2100 m达到峰值后面积开始减小,在较高和较低处几乎没有毒草害分布。草原生物灾害在坡度空间上主要集中在坡度6°~15°的缓坡,绝大部分生物灾害分布在平坡、缓坡、斜坡等坡度较小的空间内,少部分分布在急坡,陡坡和险坡几乎没有生物灾害分布。草原生物灾害各坡向均有分布,且不同坡向灾害分布面积差异不明显。②坡度对鼠害和虫害影响明显,坡向对3种生物灾害影响都不明显。③草原生物灾害分布受多地形因子共同作用,海拔与坡度之间交互作用显著,海拔与坡向的交互作用不显著。④海拔与坡度、坡向和坡度与坡向对草原鼠害、毒草害分布的影响存在显著差异;海拔与坡度对草原虫害分布的影响不存在显著差异。伊犁河谷草原生物灾害受地形影响显著,不同生物灾害类型对地形有不同响应程度,海拔和坡度交互作用呈现对草原生物灾害分布的非线性增强影响。【结论】伊犁河谷不同的草原生物灾害空间分布对地形因子的响应程度不同,交互地形因子对水热条件的调控机理是影响草原生物灾害空间分布的直接原因。通过对伊犁河谷草原生物灾害地形驱动机理的研究,可为今后伊犁河谷草原保护方案的制定与实施提供一定的科学指导与理论依据。

基于遥感生态指数的河南连康山国家级自然保护区生态环境质量时空变化研究

基于2013、2017和2021年的Landsat-8 OLI/TIRS影像,计算河南连康山国家级自然保护区的遥感生态指数(RSEI),并结合高程、坡度和坡向等数据探讨RSEI的变化与地形特征的关系。结果表明:(1)研究区2013、2017和2021年的RSEI平均值分别为0.251、0.397和0.597,呈现出逐渐上升态势,生态环境质量持续改善。核心区和缓冲区的生态环境质量不均衡发展趋势加重,实验区则趋于平衡。(2)RSEI变化以轻微改善和显著改善为主,主要集中分布于中部和南部,净改善面积为79.67 km^(2),占比75.30%。(3)中海拔(309~464 m)、坡度5°~35°以及阳坡(南、西南、西、西北)区域是RSEI降低的主要区域,建议加大该区域的保护治理力度,促进保护区生态环境质量的提升。

北京“23·7”极端强降雨特征和成因分析

利用北京地区加密气象站、补盲的北京市规划和自然资源委员会雨量站、双偏振雷达、风廓线雷达、GPS水汽等观测数据和ERA5再分析数据,对北京“23·7”极端强降雨阶段性特征和成因进行了分析。结果表明:“23·7”极端强降雨累计降水量(331 mm)和单点最大降水量(1025 mm)均打破历史纪录,最大雨强(126.6 mm·h^(-1))排名历史第二位,具有显著的极端性。强降雨可分为5个阶段,其中第Ⅱ和第Ⅳ阶段降水量分别占过程累计降水量的37.1%和39.7%,第Ⅳ阶段雨强更大,对应急流更强,高温、高湿特征也更明显。地形对降雨的增幅作用显著,降水量在海拔100~300 m山区迅速增加,极大值出现在海拔约400 m的山区,第Ⅱ(第Ⅳ)阶段山区平均降水量和小时雨强分别是平原的2.1(3.0)倍和2.0(2.7)倍;第Ⅱ阶段主要为地形对急流的直接抬升,第Ⅳ阶段为地形绕流辐合和直接抬升共同作用。7月31日上午(第Ⅳ阶段)边界层急流出口区与低空急流入口区耦合导致低层上升运动增强,促使西部山前β中尺度对流系统由块状发展成线状并有γ中尺度涡旋产生,该β中尺度对流系统北上时形成短暂的列车效应,引发了西部山区8个站次100 mm·h^(-1)以上的极端短时强降水。