Long-term regional extreme cold events(ECEs)garner significant attention due to their widespread impact and prolonged duration,posing critical threats to human society and ecosystems.Previous studies have examined ECE...Long-term regional extreme cold events(ECEs)garner significant attention due to their widespread impact and prolonged duration,posing critical threats to human society and ecosystems.Previous studies have examined ECE characteristics at single sites or grid points,however,it is crucial to recognize that such events generally manifest as spatiotemporally continuous regional phenomena.Here,we proposed an objective methodology based on spatiotemporal continuity to identify ECEs in the China-Pakistan Economic Corridor(CPEC)during the winters of 1961-2015.This approach successfully reproduced the dynamic evolution of ECEs,encompassing their initiation,development,and dissipation.We further analyzed the changes of ECE intensity,frequency,and duration,and assessed ECE trends within varying return periods by employing the generalized Pareto distribution(GPD).Our findings reveal a decline in the frequency and duration of ECEs in CPEC over the study period,while their intensity has increased by 50%.ECEs predominantly occur in the northern regions of Azad Kashmir and Balochistan’s Quetta in Pakistan,and Kashgar in China.High recurrence levels are associated with an expansion of ECE-prone areas,particularly in the northern Pamir Plateau,which emerges as a regional hotspot.These results highlight the critical need to remain vigilant to potential future surges in ECEs under global warming,underscoring their implications for regional climate resilience.展开更多
Nitrogen(N)and phosphorus(P)are essential nutrients and can significantly impact primary productivity of the ecosystem causing water environmental problems.However,their cycling mechanisms are not well understood in a...Nitrogen(N)and phosphorus(P)are essential nutrients and can significantly impact primary productivity of the ecosystem causing water environmental problems.However,their cycling mechanisms are not well understood in alpine mountains with climate change.Hence,94 samples of river water were collected from 2018 to 2020 in the headwaters of the Shule River Basin to assess the nutrients spatiotemporal distribution and combined ap-proach of water quality index to assess water quality and potential sources.The findings depict that high nutrient concentrations were found to coincide with snowmelt and glacial meltwater and rainfall recharge periods,while total flux peaked from June to September due to increased runoff.Notably,total nitrogen(TN)concentrations were significantly higher near the town,primarily attributed to the replenishment of nitrate(NO_(3)^(‒)-N)from live-stock manure.The high total P(TP)was near the glacier,which was attributed to the transportation of glacial sediments into the river,and pH was another critical factor.N was the primary nutrient limiting factor for the growth of phytoplankton in river water.Although the migration and transport of nutrients have altered with climate change,river water quality is good in alpine mountains based on an overall evaluation.These findings contribute to enriching nutrient datasets and highlight the importance of water resource management and water quality assessment in sensitive and fragile alpine mountains.展开更多
Rock avalanches frequently lead to catastrophic consequences due to their unpredictably high mobility.Numerous researchers have studied the shear behavior of granular materials under various conditions,attributing the...Rock avalanches frequently lead to catastrophic consequences due to their unpredictably high mobility.Numerous researchers have studied the shear behavior of granular materials under various conditions,attributing the high mobility to ultralow resistance.However,the underlying physical mechanism of frictional weakening remains unclear.This study utilizes the discrete element method(DEM)incorporating the fragment replacement model to simulate plane shear flows under various normal stresses(0.2 e1.2 MPa)and shear velocities(0.01e2 m/s).The findings reveal a localized shear band characterized by a J-shaped velocity profile and high granular temperature,and a concentrated distribution of weak contact forces forms at a shear velocity exceeding 0.1 m/s and normal stress above 0.6 MPa.Moreover,frictional weakening is observed with increasing normal stress from 0.2 MPa to 1.2 MPa and increasing shear velocity from 0.1 m/s to 2 m/s.The evolution of the steady-state friction coefficient can be divided into two stages:an initial stage(I)and a weakening stage(II).During stage I,the steady-state friction coefficient slightly increases until reaching a peak value.However,upon entering stage II,it gradually decreases and approaches an ultimate value.The velocity-and normal stress-dependent frictional weakening can be attributed to shear localization and embedded packing structure induced by particle breakage,respectively.Finally,an optimized m(I)model is proposed to capture the full evolution of the friction coefficient with the shear strain rate,which can improve our understanding of rock avalanche dynamics.展开更多
Glacial debris flows(GDFs) often occur in alpine regions that are subject to rapid climate change, and pose a serious threat to road systems. However, the ways that climate change impacts GDF risks along road systems ...Glacial debris flows(GDFs) often occur in alpine regions that are subject to rapid climate change, and pose a serious threat to road systems. However, the ways that climate change impacts GDF risks along road systems remain poorly understood. Aierkuran Gully, located in eastern Pamir along Karakoram Highway(KKH), is a hotspot for GDF activity and climate change, and was thus selected to investigate the GDF risk to road systems under climate change conditions. Reg CM4.6 climate data for northwestern China were selected as climate projections during baseline(2011–2020) and future periods(2031–2040) under the Representative Concentration Pathway(RCP) 8.5. To reflect the coupling effect of rainfall and melt water that triggers GDF, a glacial hydrological model DETIM that considers both factors was applied to calculate the peak debris flow discharge. A FLO-2D model was calibrated based on high-quality data collected from a detailed field investigation and historical debris flow event. The FLO-2D model was used to simulate the debris flow depth and velocity during baseline and future periods under RCP8.5. The debris flow hazard was analyzed by integrating the maximum flow depth and momentum. Road structure vulnerability was further determined based on the economic value and susceptibility of hazard-affected objects. The GDF risk along KKH was assessed based on the GDF hazard and vulnerability analysis. Our results show that climate change would lead to amplified peak debris flow discharge, trigger highermagnitude GDF, and induce more severe damage and threats to the road system. Compared with the baseline period, the debris flow damage risk for culverts and bridges would increase and the areas that inundate the road and pavement would expand. Our findings provide valuable insights for the development of mitigation strategies to adapt road systems to climate change, especially in alpine regions with highly active GDFs.展开更多
Internal erosion occurs when fine particles escape from the soil driven by seepage flow,which is considered to be the crucial factor causing the failure of earth structures filled with gravelly soil.The objective of t...Internal erosion occurs when fine particles escape from the soil driven by seepage flow,which is considered to be the crucial factor causing the failure of earth structures filled with gravelly soil.The objective of this paper is to suggest an appropriate method to assess internal erosion potential of gravelly soil.By analyzing the sensitivity of soil material to internal erosion,the variable(Dc15/df85)max and the content of coarse particles(Pc)are selected as the evaluation indexes(Dc15 and df85 are the diameters of 15%mass passing in the coarse component and 85%mass passing in the fine component,respectively).A series of gravelly soils with different particle size distributions are tested for internal erosion by the self-made permeameter.Based on the test results,an evaluation method for the internal erosion of gravelly soil is proposed.Gravelly soil is prone to internal erosion when 60%≤Pc<95%and(Dc15/df85)max≥9.5.The proposed method shows good accuracy in evaluating the internal erosion of 36 soil samples from other studies,which confirms the reliability of the method.The proposed method makes it possible to accurately assess internal erosion of gravelly soil,and an alternative method is provided for engineers to determine whether there is a risk of internal erosion in earth structures consisting of gravelly soil.展开更多
To quantitatively reveal how rock blocks falling into water affect the impulse waves,the influence of a rigid block on induced first wave and second wave is systematically investigated.The block characteristics includ...To quantitatively reveal how rock blocks falling into water affect the impulse waves,the influence of a rigid block on induced first wave and second wave is systematically investigated.The block characteristics include the initial velocity,density,volume,and incident angle,and the investigated wave behavior characteristics include the maximum kinetic energy of the water,the transformation ratio of the kinetic energy from the block to the waves,the duration of the waves,the maximum movement speed,and the maximum height and width of the waves.The coupled Eulerian-Lagrangian method(CEL)is introduced to establish the numerical models of the fluid-solid coupling,and a laboratory test of a rigid wedge sliding into water demonstrates that it can reasonably describe the dynamic behavior of a landslide-induced wave.A typical process of a block entering water and its energy variation are described and analyzed in detail.Further,the relationship between each characteristic parameter of the block and the waves is quantitatively investigated and fitted.The simulation results show that energy exchange between the block and the water is very rapid after the block collides with the water.The maximum kinetic energy,maximum velocity,duration,and side dimension of the waves mainly increase non-linearly with the above characteristic parameters of the block.The transformation ratio of the kinetic energy from the block to the water,the first wave,and the second wave are usually below 60%,45%,and 30%,respectively.The velocity of the block first decreases and then maintains a constant speed after entering the water.The displacement of the block increases linearly with the initial velocity and density of the block and exponentially increases with the block volume at different times.With the increase in the incident angle of the block,the kinetic energy and scale of the second wave increase correspondingly.展开更多
基金Under the auspices of the Key R&D Program of Xinjiang Uygur Autonomous Region(No.2022B03021)Tianshan Talent Training Program of Xinjiang Uygur Autonomous Region(No.2022TSYCLJ0011)+2 种基金Transformation of Scientific and Technological Achievements from the Qinghai Province(No.2020-SF-145)the 2020 Qinghai Kunlun Talents-leading Scientists Project(No.2020-LCJ-02)Key Program of International Cooperation,Bureau of International Cooperation,Chinese Academy of Sciences(No.131551KYSB20210030)。
文摘Long-term regional extreme cold events(ECEs)garner significant attention due to their widespread impact and prolonged duration,posing critical threats to human society and ecosystems.Previous studies have examined ECE characteristics at single sites or grid points,however,it is crucial to recognize that such events generally manifest as spatiotemporally continuous regional phenomena.Here,we proposed an objective methodology based on spatiotemporal continuity to identify ECEs in the China-Pakistan Economic Corridor(CPEC)during the winters of 1961-2015.This approach successfully reproduced the dynamic evolution of ECEs,encompassing their initiation,development,and dissipation.We further analyzed the changes of ECE intensity,frequency,and duration,and assessed ECE trends within varying return periods by employing the generalized Pareto distribution(GPD).Our findings reveal a decline in the frequency and duration of ECEs in CPEC over the study period,while their intensity has increased by 50%.ECEs predominantly occur in the northern regions of Azad Kashmir and Balochistan’s Quetta in Pakistan,and Kashgar in China.High recurrence levels are associated with an expansion of ECE-prone areas,particularly in the northern Pamir Plateau,which emerges as a regional hotspot.These results highlight the critical need to remain vigilant to potential future surges in ECEs under global warming,underscoring their implications for regional climate resilience.
基金supported by the Second Tibetan Plateau Scientific Expedition and Research Program(STEP)(No.2019QZKK0208)the National Natural Science Foundation of China(Nos.42171148 and 42330512)the Key R&D Project from the Science and Technology Department of Tibet(No.XZ202501ZY0030).
文摘Nitrogen(N)and phosphorus(P)are essential nutrients and can significantly impact primary productivity of the ecosystem causing water environmental problems.However,their cycling mechanisms are not well understood in alpine mountains with climate change.Hence,94 samples of river water were collected from 2018 to 2020 in the headwaters of the Shule River Basin to assess the nutrients spatiotemporal distribution and combined ap-proach of water quality index to assess water quality and potential sources.The findings depict that high nutrient concentrations were found to coincide with snowmelt and glacial meltwater and rainfall recharge periods,while total flux peaked from June to September due to increased runoff.Notably,total nitrogen(TN)concentrations were significantly higher near the town,primarily attributed to the replenishment of nitrate(NO_(3)^(‒)-N)from live-stock manure.The high total P(TP)was near the glacier,which was attributed to the transportation of glacial sediments into the river,and pH was another critical factor.N was the primary nutrient limiting factor for the growth of phytoplankton in river water.Although the migration and transport of nutrients have altered with climate change,river water quality is good in alpine mountains based on an overall evaluation.These findings contribute to enriching nutrient datasets and highlight the importance of water resource management and water quality assessment in sensitive and fragile alpine mountains.
基金supported by the National Key Research and Development Program of China(Grant Nos.2023YFC3008300 and 2023YFC3008302)the National Natural Science Foundation of China(Grant No.U22A20603).
文摘Rock avalanches frequently lead to catastrophic consequences due to their unpredictably high mobility.Numerous researchers have studied the shear behavior of granular materials under various conditions,attributing the high mobility to ultralow resistance.However,the underlying physical mechanism of frictional weakening remains unclear.This study utilizes the discrete element method(DEM)incorporating the fragment replacement model to simulate plane shear flows under various normal stresses(0.2 e1.2 MPa)and shear velocities(0.01e2 m/s).The findings reveal a localized shear band characterized by a J-shaped velocity profile and high granular temperature,and a concentrated distribution of weak contact forces forms at a shear velocity exceeding 0.1 m/s and normal stress above 0.6 MPa.Moreover,frictional weakening is observed with increasing normal stress from 0.2 MPa to 1.2 MPa and increasing shear velocity from 0.1 m/s to 2 m/s.The evolution of the steady-state friction coefficient can be divided into two stages:an initial stage(I)and a weakening stage(II).During stage I,the steady-state friction coefficient slightly increases until reaching a peak value.However,upon entering stage II,it gradually decreases and approaches an ultimate value.The velocity-and normal stress-dependent frictional weakening can be attributed to shear localization and embedded packing structure induced by particle breakage,respectively.Finally,an optimized m(I)model is proposed to capture the full evolution of the friction coefficient with the shear strain rate,which can improve our understanding of rock avalanche dynamics.
基金This research was jointly funded by the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA20030301)the Comprehensive Investigation and Assessment of Natural Hazards in China-Pakistan Economic Corridor(Grant No.2018FY100506)+1 种基金the Second Tibetan Plateau Scientific Expedition and Research Program(STEP)(Grant No.2019QZKK0906)the International Science&Technology Cooperation Program of China(Grant No.2018YFE0100100)。
文摘Glacial debris flows(GDFs) often occur in alpine regions that are subject to rapid climate change, and pose a serious threat to road systems. However, the ways that climate change impacts GDF risks along road systems remain poorly understood. Aierkuran Gully, located in eastern Pamir along Karakoram Highway(KKH), is a hotspot for GDF activity and climate change, and was thus selected to investigate the GDF risk to road systems under climate change conditions. Reg CM4.6 climate data for northwestern China were selected as climate projections during baseline(2011–2020) and future periods(2031–2040) under the Representative Concentration Pathway(RCP) 8.5. To reflect the coupling effect of rainfall and melt water that triggers GDF, a glacial hydrological model DETIM that considers both factors was applied to calculate the peak debris flow discharge. A FLO-2D model was calibrated based on high-quality data collected from a detailed field investigation and historical debris flow event. The FLO-2D model was used to simulate the debris flow depth and velocity during baseline and future periods under RCP8.5. The debris flow hazard was analyzed by integrating the maximum flow depth and momentum. Road structure vulnerability was further determined based on the economic value and susceptibility of hazard-affected objects. The GDF risk along KKH was assessed based on the GDF hazard and vulnerability analysis. Our results show that climate change would lead to amplified peak debris flow discharge, trigger highermagnitude GDF, and induce more severe damage and threats to the road system. Compared with the baseline period, the debris flow damage risk for culverts and bridges would increase and the areas that inundate the road and pavement would expand. Our findings provide valuable insights for the development of mitigation strategies to adapt road systems to climate change, especially in alpine regions with highly active GDFs.
基金financially supported by the National Natural Science Foundation of China(Grant No.41790432)Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA20030301)。
文摘Internal erosion occurs when fine particles escape from the soil driven by seepage flow,which is considered to be the crucial factor causing the failure of earth structures filled with gravelly soil.The objective of this paper is to suggest an appropriate method to assess internal erosion potential of gravelly soil.By analyzing the sensitivity of soil material to internal erosion,the variable(Dc15/df85)max and the content of coarse particles(Pc)are selected as the evaluation indexes(Dc15 and df85 are the diameters of 15%mass passing in the coarse component and 85%mass passing in the fine component,respectively).A series of gravelly soils with different particle size distributions are tested for internal erosion by the self-made permeameter.Based on the test results,an evaluation method for the internal erosion of gravelly soil is proposed.Gravelly soil is prone to internal erosion when 60%≤Pc<95%and(Dc15/df85)max≥9.5.The proposed method shows good accuracy in evaluating the internal erosion of 36 soil samples from other studies,which confirms the reliability of the method.The proposed method makes it possible to accurately assess internal erosion of gravelly soil,and an alternative method is provided for engineers to determine whether there is a risk of internal erosion in earth structures consisting of gravelly soil.
基金funded by the Second Tibetan Plateau Scientific Expedition and Research Program (STEP) (Grant No. 2021QZKK0202)the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDA20030301)+1 种基金the National Natural Science Foundation (Grant No. 41790432 and U22A20603)the fellowship of China Postdoctoral Science Foundation (Grant No. 2020M683369)
文摘To quantitatively reveal how rock blocks falling into water affect the impulse waves,the influence of a rigid block on induced first wave and second wave is systematically investigated.The block characteristics include the initial velocity,density,volume,and incident angle,and the investigated wave behavior characteristics include the maximum kinetic energy of the water,the transformation ratio of the kinetic energy from the block to the waves,the duration of the waves,the maximum movement speed,and the maximum height and width of the waves.The coupled Eulerian-Lagrangian method(CEL)is introduced to establish the numerical models of the fluid-solid coupling,and a laboratory test of a rigid wedge sliding into water demonstrates that it can reasonably describe the dynamic behavior of a landslide-induced wave.A typical process of a block entering water and its energy variation are described and analyzed in detail.Further,the relationship between each characteristic parameter of the block and the waves is quantitatively investigated and fitted.The simulation results show that energy exchange between the block and the water is very rapid after the block collides with the water.The maximum kinetic energy,maximum velocity,duration,and side dimension of the waves mainly increase non-linearly with the above characteristic parameters of the block.The transformation ratio of the kinetic energy from the block to the water,the first wave,and the second wave are usually below 60%,45%,and 30%,respectively.The velocity of the block first decreases and then maintains a constant speed after entering the water.The displacement of the block increases linearly with the initial velocity and density of the block and exponentially increases with the block volume at different times.With the increase in the incident angle of the block,the kinetic energy and scale of the second wave increase correspondingly.
