Extracting water body data based on SDWI and threshold segmentation:A case study in permafrost area surrounding Salt Lake in Hoh Xil,Qinghai-Tibet Plateau,China

There are a large number of lakes,rivers,and other natural water bodies distributed in the permafrost area of the Qinghai-Tibet Plateau(QTP).The changes in water bodies will affect the distribution of water resources in sur-rounding areas and downstream areas,resulting in environmental impact and bringing potential flood disasters,which will induce more serious issues and problems in alpine and high-altitude areas with a fragile habitat(such as the QTP in China).Generally,effective,reasonable,and scientific monitoring of large-scale water bodies can not only document the changes in water bodies intuitively,but also provide important theoretical reference for subsequent environmental impact prediction,and disaster prevention and mitigation in due course of time.The large-scale water extraction technology derived from the optical remote sensing(RS)image is seriously affected by clouds,bringing about large differences among the extracted water result products.Synthetic aperture radar(SAR)RS technology has the unique advantage characteristics of all-weather,all-day,strong penetration,and not being affected by clouds,which is hopeful in extracting water body data,especially for days with cloudy weather.The data extraction of large-scale water bodies based on SAR images can effectively avoid the errors caused by clouds that become prevalent at present.In this paper,the Hoh Xil Salt Lake on the QTP and its surrounding five lakes are taken as the research objects.The 2-scene Sentinel-1 SAR image data covering the whole area on 22 August 2022 was used to verify the feasibility of extracting water body data in permafrost zones.Furthermore,on 22 August 2022,the wealth here was cloudy,which made the optical RS images,e.g.,Sentinel-2 images full of clouds.The results show that:using the Sentinel-1 image and threshold segmentation method to extract water body data is efficient and effective with excellent results in permafrost areas.Concretely,the Sentinel-1 dual-polarized water index(SDWI),calculated by combining dual vertical–vertical(VV)polarized and verti-cal–horizontal(VH)polarized data is a useful index for water extraction and the result is better than each of the VV or VH polarized images.

STREAMFLOW CHARACTERISTICS OF THE EASTERN QINGHAI-XIZANG PLATEAU

The eastern Qinghai-Xizang (Tibet) Plateau is the headwater area for many large Asian rivers. Permafrost occurs above 4,200 m a.s.l. and glaciers occupy the summits and high valleys of the east-west trending mountain chains. Annual runoff generally increases with precipitation which is augmented southward by the rise in topography. Rainfall, snow melt, glacier melt and groundwater are the primary sources of stream flow, and the presence of permafrost enhances the flashiness of runoff response to rainfall and snowmelt events. Peak flows are concentrated between June and September. And winter is low flow season. Three types of runoff patterns may be distinguished according to their primary sources of water supply: snowmelt and rainfall, glacier melt and snowmelt, and groundwater. Large rivers generally drain more than one environments and their runoff regime reflects an integration of the various flow patterns on the plateau.

Change trend of natural gas hydrates in permafrost on the Qinghai-Tibet Plateau(1960-2050)under the background of global warming and their impacts on carbon emissions

Global warming and the response to it have become a topic of concern in today’s society and are also a research focus in the global scientific community.As the world’s third pole,the global warming amplifier,and the starting region of China’s climate change,the Qinghai-Tibet Plateau is extremely sensitive to climate change.The permafrost on the Qinghai-Tibet Plateau is rich in natural gas hydrates(NGHs)resources.Under the background of global warming,whether the NGHs will be disassociated and enter the atmosphere as the air temperature rises has become a major concern of both the public and the scientific community.Given this,this study reviewed the trend of global warming and accordingly summarized the characteristics of the temperature increase in the Qinghai-Tibet Plateau.Based on this as well as the distribution characteristics of the NGHs in the permafrost on the Qinghai-Tibet Plateau,this study investigated the changes in the response of the NGHs to global warming,aiming to clarify the impacts of global warming on the NGHs in the permafrost of the plateau.A noticeable response to global warming has been observed in the Qinghai-Tibet Plateau.Over the past decades,the increase in the mean annual air temperature of the plateau was increasingly high and more recently.Specifically,the mean annual air temperature of the plateau changed at a rate of approximately 0.308-0.420℃/10a and increased by approximately 1.54-2.10℃in the past decades.Moreover,the annual mean ground temperature of the shallow permafrost on the plateau increased by approximately 1.155-1.575℃and the permafrost area decreased by approximately 0.34×10^(6)km^(2) from about 1.4×10^(6)km^(2) to 1.06×10^(6)km^(2) in the past decades.As indicated by simulated calculation results,the thickness of the NGH-bearing permafrost on the Qinghai-Tibet Plateau has decreased by 29-39 m in the past 50 years,with the equivalent of(1.69-2.27)×10^(10)-(1.12-1.51)×10^(12)m^(3) of methane(CH_(4))being released due to NGHs dissociation.It is predicted that the thickness of the NGH-bearing permafrost will decrease by 23 m and 27 m,and dissociated and released NGHs will be the equivalent of(1.34-88.8)×10^(10)m^(3) and(1.57-104)×10^(10)m^(3)of CH_(4),respectively by 2030 and 2050.Considering the positive feedback mechanism of NGHs on global warming and the fact that CH_(4) has a higher greenhouse effect than carbon dioxide,the NGHs in the permafrost on the Qinghai-Tibet Plateau will emit more CH_(4) into the atmosphere,which is an important trend of NGHs under the background of global warming.Therefore,the NGHs are destructive as a time bomb and may lead to a waste of efforts that mankind has made in carbon emission reduction and carbon neutrality.Accordingly,this study suggests that human beings should make more efforts to conduct the exploration and exploitation of the NGHs in the permafrost of the Qinghai-Tibet Plateau,accelerate research on the techniques and equipment for NGHs extraction,storage,and transportation,and exploit the permafrost-associated NGHs while thawing them.The purpose is to reduce carbon emissions into the atmosphere and mitigate the atmospheric greenhouse effect,thus contributing to the global goal of peak carbon dioxide emissions and carbon neutrality.

Recent advances in hydrology studies under changing permafrost on the Qinghai-Xizang Plateau

Due to the great influences of both climate warming and human activities,permafrost on the Qinghai-Xizang Plateau(QXP) has been undergoing considerable degradation.Continuous degradation of plateau permafrost dramatically modifies the regional water cycle and hydrological processes,affecting the hydrogeological conditions,and ground hydrothermal status in cold regions.Permafrost thawing impacts the ecological environment,engineering facilities,and carbon storage functions,releasing some major greenhouse gases and exacerbating climate change.Despite the utilization of advanced research methodologies to investigate the changing hydrological processes and the corresponding influencing factors in permafrost regions,there still exist knowledge gaps in multivariate data,quantitative analysis of permafrost degradation's impact on various water bodies,and systematic hydrological modeling on the QXP.This review summarizes the main research methods in permafrost hydrology and elaborates on the impacts of permafrost degradation on regional precipitation distribution patterns,changes in surface runoff,expansion of thermokarst lakes/ponds,and groundwater dynamics on the QXP.Then,we discuss the current inadequacies and future research priorities,including multiple methods,observation data,and spatial and temporal scales,to provide a reference for a comprehensive analysis of the hydrological and environmental effects of permafrost degradation on the QXP under a warming climate.

Permafrost environment monitoring on the Qinghai-Tibet Plateau using time series ASAR images

The permafrost in Qinghai-Tibet Plateau(QTP)has long been the focus of many researchers.In this study,we first use the method that integrates synthetic aperture radar(SAR)intensity and phase information to monitor permafrost environment in the Beiluhe Region,using time series advanced SAR images.The backscattering coefficients(σ^(0))and deformation were extracted for the main features,and the influences of meteorological conditions to them were also quantified.The results show that both the change inσ^(0)and surface deformation are closely related to the active layer,and the deformation is also affected by the permafrost table.First,over meadow and sparse vegetation regions,σ^(0)rose about 6.9 and 4 dB from the freezing to thawing period,respectively,which can be mainly attributed to the thaw of the active layer and increased precipitation.Second,seasonal deformation,derived from the freeze-thaw cycle of the active layer,was characteristic of frost heave and thaw settlement and exhibited a negative correlation with air temperature.Its magnitude was larger than 1 cm in a seasonal cycle.Last,significant secular settlement was observed,with rates ranging from-16 to 2 mm/a,and it was primarily due to the thaw of the permafrost table caused by climate warming.

The future thermal regime of numerical simulating permafrost on Qinghai-Xizang (Tibet) Plateau, China, under climate warming

Numerical simulation indicates that the future thermal regime of permafrost on Qinghai-Xizang Plateau will change as the air temperature continuously rises at 0.04℃/a. The calculated results show that when Ts are 0, -0.5, -1.5, -2.5, -3.5 and - 4.5℃ under equilibium between climate and permafrost thermal regime, the mean annual temperatures at the depth of 14 m correspondingly equal to -0.11, -0.59, -1.52, -2.45, -3.21 and -4.32℃, and the permafrost thicknesses respectively equal to 16.8, 29.0, 54.1, 79.4, 112.1 and 131.0m. 50 years later, the temperatures at the depth of 14m will rises to 0.0, 0.0, -0.36, -1.23, -2.16, -3.06℃ under the given condition. When TS is lower than -1.1℃, the permafrost will respectively change from initial 2.0, 1.8, 1.6, 1.4m to 2.2, 2.0, 1.8, 1.6m for TS=-1.5, -2.5. - 3.5 and -4.5℃. If TS is higher than - 1.1℃, the frozen ground will change from the attachment type of frozen ground into the detachment type of frozen ground. Therefore, if future air temperature rises at 0.04℃ a or lower, the decrease area of the permafrost on Qinghai-Xizang Plateau may not be over 30℃. The areas includes those changing from the attachment of frozen ground into the detachment of frozen ground. If the area of detachment of frozen ground is not included, the decrease area may only be 3℃ within 50 a.

人类活动对青藏高原冻土环境的影响

采用物探技术、植物样方调查对青藏公路沿线工程活动对冻土环境因素之间的影响进行了分析研究,结果表明:由于工程活动对原冻土区地貌、植被及表土层结构等的干扰破坏,致使工程区及其影响区冻土上限下降速度加快,同时得出了冻结层上水埋深(1～3m)与冻土层厚度变化的关系以及冻结层上水水位随冻土上限下降而变化的规律.指出工程活动对植被的影响不仅与工程本身有关,也与工程区冻土厚度、地下水、土壤等因素有密切关系.

青藏高原开发中的冻土问题

在国家决策西部大开发战略之际，正确评价青藏高原开发中所面临的冻土问题，为生态环境建设和国民经济持续稳定发展提供依据，显得更为重要。多年冻土占据着青藏高原一半以上的疆土面积，受全球气候变化和人为活动的共同影响，在过去的几十年中已发生了不同程度的变化，且随着人类活动增强，变化必将加剧，冻土问题也将显得日益突出。多年冻土的变化主要表现为多年冻土的地温升高、上限下降和面积缩减等，进而影响到各类工程的地基稳定性，使工程建筑受到不同程度的破坏；同时，由于气候变化、过度放牧和工程活动的影响，地面水热状况改变，尤其是地表土壤层中水分含量的降低，导致了草场退化，生态环境恶化。在分析这些冻土问题原因的基础上，作者预测了在未来开发中可能出现的冻土问题，并提出了建议。

青藏高原东部多年冻土退化对环境的影响

退化是本区多年冻土变化的基本趋势,不同区段退化幅度有差异,影响退化的因素除了全球气候转暖外,还有局地气候和地下水迳流。在退化敏感的地带,工程建设,牧区生态平衡都有不可忽视的影响。

再论青藏高原苔原:地球第三极地理极性之确认

青藏高原是否存在苔原,关系到地球是否有地理意义的第三极——高极,因此其是全球地理科学的一个基本问题。在给出苔原定义的基础上,拟定了由5个要素组成的苔原环境指标组合。这5个要素分别是7月平均气温为0℃～10℃;位于冰盖或冰川外围的冰缘区,寒冻强烈;存在多年冻土;土壤为寒冻土;植被无林。青藏高原7月平均气温介于0℃～10℃的范围约占高原面积的50.4%,为129.64×104 km2;在此范围内,山谷冰川广泛分布,现代冰缘环境典型,寒冻过程强烈;连续多年冻土占高原多年冻土面积的72.5%,土壤为寒冻土,且冰沼土发育;植被因海拔高度突破森林线而无林,仅有小灌丛、草类及苔藓等;因此,判定青藏高原存在苔原。青藏高原沼泽湿地植物多特有种,冻胀泥炭丘普遍,与多边形土等形成冻胀组合,构成沼泽苔原。高原外围山地发育山地苔原,中部发育高原苔原。青藏高原具有山原性质,因此有世界唯一的山原苔原,表现出苔原的多样性。中国除长白山、阿尔泰山和天山以外不存在苔原的传统观点是不正确的,青藏高原苔原才是中国苔原的南缘。高原苔原的发现将从地理环境上确认青藏高原全球第三极的地理极性,这对深化高原环境认识具有重要意义。

青藏高原多年冻土区高速公路选线研究

针对青藏高原多年冻土区的路线选线工作,结合青藏高速公路的勘察设计,分析了青藏高原的建设特点及各种控制因素对高速公路选线的影响,提出了青藏高原多年冻土区高速公路选线的基本原则,并结合实际工程进行了路线方案的选线研究。

青藏高原与天山山地多年冻土地区生态环境状况的比较分析——以青藏公路格拉段与天山公路独库段为例

以青藏公路格拉段与天山公路独库段为案例,在确定了两路段所穿越的多年冻土分布区的基础上,比较了青藏高原与天山山地多年冻土地区生态环境状况的差异性。这两个多年冻土地区生态环境的差别集中体现在多年冻土层和植被上。公路工程对青藏高原多年冻土地区的多年冻土层、植被、野生动物、水土流失,地表水系等都有影响,但对天山山地多年冻土地区的生态环境影响因生态环境特征的不同而出现差异,集中体现在地表水系所受的影响更大,且水土流失更为严重。

青藏高原线型工程及其生态环境研究

“世界屋脊”的青藏高原是中低纬地带面积最大的高原多年冻土区。该区的生态环境和地质环境十分脆弱 ,而线型工程本身的特点加之施工管理不当 ,会造成沿线冻土环境和生态环境的恶化。本文探讨了该区线型工程及其沿线生态环境的相互作用机制 。

Impacts of permafrost changes on alpine ecosystem in Qinghai-Tibet Plateau

Alpine cold ecosystem with permafrost environment is quite sensitive to climatic changes and the changes in permafrost can significantly affect the alpine ecosystem. The vegetation coverage, grassland biomass and soil nutrient and texture are selected to indicate the regime of alpine cold ecosystems in the Qinghai-Tibet Plateau. The interactions between alpine ecosystem and permafrost were investigated with the depth of active layer, permafrost thickness and mean annual ground temperature (MAGTs). Based on the statistics model of GPTR for MAGTs and annual air temperatures, an analysis method was developed to analyze the impacts of permafrost changes on the alpine ecosystems. Under the climate change and human engineering activities, the permafrost change and its impacts on alpine ecosystems in the permafrost region between the Kunlun Mountains and the Tanggula Range of Qinghai-Tibet Plateau are studied in this paper. The results showed that the per- mafrost changes have a different influence on different alpine ecosystems. With the increase in the thickness of active layer, the vegetation cover and biomass of the alpine cold meadow exhibit a significant conic reduction, the soil organic matter content of the alpine cold meadow ecosystem shows an exponential decrease, and the surface soil materials become coarse and gravelly. The alpine cold steppe ecosystem, however, seems to have a relatively weak relation to the permafrost environment. Those relationships resulted in the fact that the distribution area of alpine cold meadow decreased by 7.98% and alpine cold swamp decreased by 28.11% under the permafrost environment degradation during recent 15 years. In the future 50 years the alpine cold meadow ecosystems in different geomorphologic units may have different responses to the changes of the permafrost under different climate warming conditions, among them the alpine cold meadow and swamp ecosystem located in the low mountain and plateau area will have a relatively serious degradation. Furthermore, from the angles of grassland coverage and biological production the variation characteristics of high-cold eco- systems in different representative regions and different geomorphologic units under different climatic conditions were quantitatively assessed. In the future, adopting effective measures to protect permafrost is of vital importance to maintaining the stability of permafrost engineering and alpine cold eco- systems in the plateau.

Linkage between the second uplifting of the Qinghai-Xizang (Tibetan) Plateau and the initiation of the Asian monsoon system

During the period from 25 to 17 Ma BP, when the second plateau uplifting, i.e. the second phase of the Himalaya movement, occurred, the Qinghai-Xizang Plateau reached an altitude high enough to chbge the situation of the general circulation. Such an effect of the plateau on the atmospheric circulation was accompanied by the warrning of the tropical ocean, the enhancement of the cross equatorial current, the enlargement of the marginal sea basins in the east-southeastern Asia, the westward extending of the Asian continent and the regression of the Paratethys Sea. As a result, the thermal difference was enlarged, and the air currents were enhanced between continents and oceans; finally the Asian monsoon system, mainly the summer monsoon, was initiated. The former planet wind system was then substituted by the monsoon system, and this caused the important environmental changes, such as the large shrinkage of the dry steppe in Central Asia, and the extension of the humid forest zone in East Asia. Thme changes have been dated at 21.8 Ma BP on the Lingxia profile in the northeastern border of the Tibet Plateau, when the savanna was transformed into the forest.

祁连山木里矿区冻土资源分布特征及其环境效应

祁连山冻土资源广泛发育,冻土类型受地貌、地下水、岩性、地表植被等条件的影响复杂多变。近年来,在全球气候趋于变暖和人类活动的综合影响下,祁连山冻土资源面临着稳定性降低,多样性遭受破坏等问题,由此导致植被面积减退、水土流失加剧等。因此,保护祁连山地区冻土资源,建立长期动态监测体系迫在眉睫。本文利用以往钻孔测温及热红外遥感影像资料,对祁连山木里矿区冻土资源的特征、类型、分布、生态环境效应,以及人类活动对其产生的影响进行了探讨,以期对祁连山地区冻土资源保护提供参考资料。