Performance validation of High Mountain Asia 8-meter Digital Elevation Model using ICESat-2 geolocated photons

High Mountain Asia(HMA),recognized as a third pole,needs regular and intense studies as it is susceptible to climate change.An accurate and high-resolution Digital Elevation Model(DEM)for this region enables us to analyze it in a 3D environment and understand its intricate role as the Water Tower of Asia.The science teams of NASA realized an 8-m DEM using satellite stereo imagery for HMA,termed HMA 8-m DEM.In this research,we assessed the vertical accuracy of HMA 8-m DEM using reference elevations from ICESat-2 geolocated photons at three test sites of varied topography and land covers.Inferences were made from statistical quantifiers and elevation profiles.For the world’s highest mountain,Mount Everest,and its surroundings,Root Mean Squared Error(RMSE)and Mean Absolute Error(MAE)resulted in 1.94 m and 1.66 m,respectively;however,a uniform positive bias observed in the elevation profiles indicates the seasonal snow cover change will dent the accurate estimation of the elevation in this sort of test sites.The second test site containing gentle slopes with forest patches has exhibited the Digital Surface Model(DSM)features with RMSE and MAE of 0.58 m and 0.52 m,respectively.The third test site,situated in the Zanda County of the Qinghai-Tibet,is a relatively flat terrain bed,mostly bare earth with sudden river cuts,and has minimal errors with RMSE and MAE of 0.32 m and 0.29 m,respectively,and with a negligible bias.Additionally,in one more test site,the feasibility of detecting the glacial lakes was tested,which resulted in exhibiting a flat surface over the surface of the lakes,indicating the potential of HMA 8-m DEM for deriving the hydrological parameters.The results accrued in this investigation confirm that the HMA 8-m DEM has the best vertical accuracy and should be of high use for analyzing natural hazards and monitoring glacier surfaces.

Changes in equilibrium-line altitude and implications for glacier evolution in the Asian high mountains in the 21st century

In the context of global warming,glaciers in the Asian High Mountains(AHMs)are shrinking at an accelerating rate.Projecting their future change is helpful for understanding the hydrological and climatic effects related to glacier retreat.Here,we projected glacier change in the AHMs from 1979 to 2100 under shared socioeconomic pathway(SSP)scenarios from the perspective of temperature,equilibrium-line altitude(ELA),and accumulation area.The annual mean temperature in the AHMs increased by 1.26℃ from 1979 to 2014,corresponding to an increase of 210 m in the mean ELA and a decrease of 1.7×10^(4)km^(2) in the glacier accumulation area.Under the SSP2-4.5(SSP5-8.5)scenario,the annual mean temperature in the AHMs would increase by 2.84℃(3.38℃)in 2040–2060 relative to that in 1850–1900,leading to the mean ELA reaching an elevation of5661 m(5777 m).The accumulation area in the AHMs decreased by 46.3%from 1995 to 2014 and was projected to decrease by60.1%in 2040–2060.Moreover,the annual mean temperature in the AHMs was projected to increase by 3.76℃(6.44℃)in2080–2100 relative to that in 1850–1900,corresponding to the ELA reaching an elevation of 5821 m(6245 m)and the accumulation area decreasing to 1.8×10^(4)km^(2)(0.5×10^(4)km^(2)).These data suggest that the conditions for glacier development will disappear in most of the AHMs,except for extreme high-altitude regions in the Tianshan,Pamir,and Himalaya Mountains.Under the SSP2-4.5(SSP5-8.5)scenario,when the global mean temperature increases 1.5℃(2℃)above pre-industrial levels,the annual mean temperature will increase by 2.12℃(2.86℃)and the accumulation area will decrease by 15%(48%)in the AHMs compared with that in 1995–2015.Therefore,a 1.5℃ increase in global warming would keep 40%more of the glacial accumulation area(1.5×10^(4)km^(2))in the AHMs compared to a 2℃ increase in global warming.

Long-term changes and periodicity of ice phenomena in the high mountain Lake Morskie Oko(Tatra Mountains,Western Carpathians)

High montain lakes are regarded as sensitive indicators of environmental changes in local and global scales.In recent years,climate change has considerablely influenced the timing of ice phenomena in these lakes.The objective of the paper is an investigation of long-term changes and periodicity of ice phenomena in high mountain Lake Morskie Oko(1392.8 m a.s.l.)located in the Tatra Mts.in the period 1971-2020.The study employed the Lomb-Scargle periodogram,linear regression modelling for temporal trends,correlation analysis,parameters of variability,and flashiness index.Periodicity of the duration of ice phenomena(~5.4 y)and ice cover on the lake(~13.5 y)was observed,although both are statistically insignificant.Ice cover duration has been interrupted several times by winter thaws after 1996 whereas no such events had been reported earlier.The trend towards a delayed appearance of ice phenomena reaches 4.0 d·decade^(-1)(p<0.001).The observed trend towards an earlier ice phenomena disappearance reaches 5.1 d·decade^(-1)(p<0.001).It results in a decline of the number of days with ice phenomena on Lake Morskie Oko at a rate of 9.0 d·decade^(-1)(p<0.001).The duration of ice cover on Lake Morskie Oko has been decreasing at a rate of 10.4 d·decade^(-1).It is attributed to later freezeup(3.9 d·decade^(-1),p<0.001)and earlier ice break-up(5.6 d·decade^(-1),p<0.001).An increasing trend of average annual air temperature(0.4°C·decade^(-1),p<0.001)in the period 1971-2020 is observed.A statistically significant correlation is recorded between ice phenomena and ice cover(beginning,end,duration),average annual air temperature,average air temperature of three summer months(June,July,August),and average air temperature of the six months period from June to November.Higher air temperature induces growing heat resources accumulated in the lake water in the summer and autumn seasons,potentially causing later initiation of ice phenomena in the lake.There is no statistically significant relationship between maximum ice thickness and any air temperature parameters.Variability of maximum ice thickness appears to have been significantly increasing in the second part of the investigated period(1996-2020).

1991-2020 climate normal in the European Alps:focus on high-elevation environments

Alps are an important geographical area of the European continent and,in this area,temperature increase is most evident.However,the 1991-2020 climate normal in the Alps has still not been thoroughly investigated.Aiming to fill this gap with a focus on high-elevation environments,minimum and maximum daily air temperature acquired by 23 automatic weather station were used.The results show that the mean annual values of minimum and maximum temperature for the 1991-2020 climate normal in the Alps are-2.4℃ and 4.4℃,respectively,with a warming rate of 0.5℃/10 years.The mean annual temperature comparison between 1961-1990 and 1971-2000,1961-1990 and 1981-2010,1961-1990 and 1991-2020 climate normal show an increase of 0.3℃,0.5℃ and 0.9℃,respectively.The results also confirm that seasonal and annual temperatures are rising through the whole Alpine arc,mainly in summer and autumn.This work highlights that annual minimum and maximum temperature do not seem to be affected by a positive elevation-dependent warming.Instead,a positive elevation-dependent warming in the maximum values of the annual minimum temperature was found.If anthropogenic emissions maintain the trend of the last decades,the expected mean annual temperature of the 2001-2030 climate normal is-0.2℃,with an increase of 0.5℃ if compared to the 1991-2020 climate normal and with an increase of 1.5℃ if compared to the 1961-1990 climate normal.This study highlights the warming rate that is now present in the European Alps,provides indications on the warming rate that will occur in the coming years and highlights the importance of carrying out investigations that consider not only the last 30-year climate normal,but also the most recent 30-year climate normal by comparing them with each other.

Performance evaluation of CLM5.0 in simulating liquid soil water in high mountainous area,Northwest China

The model performance in simulating soil water content(SWC) is crucial for successfully modeling earth’s system,especially in high mountainous areas.In this study,the performance of Community Land Model 5.0(CLM5.0) in simulating liquid SWC was evaluated against observations from nine in-situ sites in the upper reach of the Heihe River Watershed(HRW),Northwest China.The CLM5.0 shows reliable performance in the study area with correlation coefficients(R) ranging between 0.79–0.93,root mean standard errors(RMSE)ranging between 0.044–0.097 m^(3)/m^(3),and the mean bias(BIAS) ranging between-0.084–0.061 m^(3)/m^(3).The slightly worse performance of CLM5.0 than CLM4.5 on alpine meadow and grassland is mainly caused by the revised canopy interception parameterization.The CLM5.0 overestimates interception and underestimates evapotranspiration(ET) on both alpine meadow and grassland during the growth period.The systematical overestimations at all the grassland sites indicate that the underestimation of ET is much larger than the overestimation of interception on grassland during growth period,while the errors of simulated interception and ET are partially canceled out on alpine meadow.Moreover,the underestimation of ET is more responsible for the overestimation of SWC than the overestimation of interception in the high mountainous area.It is necessary to estimate reasonable empirical parameter α(proportion of leaf water collection area) in interception parameterization scheme and further improve the dry surface layerbased soil evaporation resistance parameterization introduced in CLM5.0 in future researches.The performance of CLM5.0 is better under completely frozen stage than thawing stage and freezing stage,because of low variations of liquid SWC caused by extremely low hydraulic conductivity of soils.The underestimation of liquid SWC under frozen state is caused by underestimation of soil temperature,which leads to more ice mass and less liquid water in total water content.

Seasonal variations in glacier velocity in the High Mountain Asia region during 2015–2020

Velocity is an important component of glacier dynamics and directly reflects the response of glaciers to climate change.As a result,an accurate determination of seasonal variation in glacier velocity is very important in understanding the annual variation in glacier dynamics.However,few studies of glacier velocity in the High Mountain Asia(HMA)region were done.Along these lines,in this work,based on Sentinel-1 glacier velocity data,the distribution of glacier velocity in the HMA region was plotted and their seasonal variations during 2015-2020 were systematically analysed.The average glacier velocity in the HMA region was 0.053 m/d,and was positively correlated with the glacier area and slope.Glaciers in the Karakoram Mountains had the fastest average flow velocity(0.060 m/d),where the glaciers exhibited the largest average area and average slope.Moreover,glaciers in the GangdisêMountains had the slowest velocity(0.022 m/d)and the smallest average glacier area.The glacier flows were the fastest in spring(0.058 m/d),followed by summer(0.050 m/d),autumn(0.041 m/d),and winter(0.040 m/d).In addition,the glacier flows were the maximum in May,being 1.4 times of the annual average velocity.In some areas,such as the Qilian,Altun,Tibetan Interior,Eastern Kunlun,and Western Kunlun mountains,the peak glacier velocities appeared in June and July.The glacier velocity in the HMA region decreased in midsummer and reached the minimum in December when it was 75%of the annual average.These results highlight the role of meltwater in the seasonal variation in glacier flows in late spring and early summer.The seasonal velocity variation of lake-terminating glaciers was similar to that of land-terminating ones,but the former flowed faster.The velocity difference close to the mass balance line between the lake-and land-terminating glaciers was obviously greater in spring than in other seasons.In summer,the difference between the lake-and land-terminating glaciers at a normalized distance of 0.05-0.40 from the terminus was significantly greater than those of other seasons.The velocity difference between the lake-and land-terminating glaciers is closely related to the variable of ice thickness,and also to the frictional force of the terminal base reduced by proglacial lakes.Thus,it can be concluded that in addition to the variation of the glacier thickness and viscosity,the variation of glacier water input also plays a key role in the seasonal variation of glacier velocity.

Annual and seasonal changes of the air temperature with altitude in the Upper Dades valley, High Atlas, Morocco

The purpose of this study is to determine the size of air temperature changes with altitude in the mountains of the arid zone, on the example of the Upper Dades valley(High Atlas, Morocco). The air temperature change with altitude was determined on the basis of 5 years data from three meteorological stations. The analysis was carried out on an annual and seasonal basis. The annual and daily variations of thermal gradients between pairs of stations were also determined. It was found that the average thermal gradient in the Upper Dades valley was-1.02℃ per 100 m. The highest values of the thermal gradient occur in winter and the lowest in summer. In winter,the thermal gradient was characterized by the greatest variability. Minima of the daily variation of air temperature gradients were observed in early morning hours and maxima around midday. In the lower part of the valley, air temperature inversion frequently developed between 10 AM and 3 PM UTC.The obtained results show high thermal gradients in the mountains of the arid zone, with their annual amplitude increasing in the lower parts of the valley.The instantaneous values of the gradients were significantly modified by the supply of latent heat and the occurrence of dust storms. It has been shown that the advection factor plays an important role in shaping large gradient values. The study contains novel results of thermal gradient measurements in high mountains of arid zone.

Glacier mass balance in High Mountain Asia inferred from a GRACE release-6 gravity solution for the period 2002–2016

We provide estimates of glacier mass changes in the High Mountain Asia (HMA) area from April2002 to August 2016 by employing a new version of gravity solutions of the Gravity Recovery and ClimateExperiment (GRACE) twin-satellite mission. We find a total mass loss trend of the HMA glaciers at a rateof –22.17 (±1.96) Gt/a. The largest mass loss rates of –7.02 (±0.94) and –6.73 (±0.78) Gt/a are found forthe glaciers in Nyainqentanglha Mountains and Eastern Himalayas, respectively. Although most glaciers inthe HMA area show a mass loss, we find a small glacier mass gain of 1.19 (±0.55) and 0.77 (±0.37) Gt/a inKarakoram Mountains and Western Kunlun Mountains, respectively. There is also a nearly zero massbalance in Pamirs. Our estimates of glacier mass change trends confirm previous results from the analysisof altimetry data of the ICESat (ICE, Cloud and Land Elevation Satellite) and ASTER (AdvancedSpaceborne Thermal Emission and Reflection Radiometer) DEM (Digital Elevation Model) satellites inmost of the selected glacier areas. However, they largely differ to previous GRACE-based studies which weattribute to our different post-processing techniques of the newer GRACE data. In addition, we explicitlyshow regional mass change features for both the interannual glacier mass changes and the 14-a averagedseasonal glacier mass changes. These changes can be explained in parts by total net precipitation (netsnowfall and net rainfall) and net snowfall, but mostly by total net radiation energy when compared to datafrom the ERA5-Land meteorological reanalysis. Moreover, nearly all the non-trend interannual masschanges and most seasonal mass changes can be explained by the total net radiation energy data. The massloss trends could be partly related to a heat effect due to increased net rainfall in Tianshan Mountains, QilianMountains, Nyainqentanglha Mountains and Eastern Himalayas. Our new results for the glacier mass changein this study could help improve the understanding of glacier variation in the HMA area and contribute tothe study of global change. They could also serve the utilization of water resources there and in neighboringareas.

Spatial variability between glacier mass balance and environmental factors in the High Mountain Asia

High Mountain Asia(HMA) region contains the world’s highest peaks and the largest concentration of glaciers except for the polar regions, making it sensitive to global climate change. In the context of global warming, most glaciers in the HMA show various degrees of negative mass balance,while some show positive or near-neutral balance. Many studies have reported that spatial heterogeneity in glacier mass balance is strongly related to a combination of climate parameters. However, this spatial heterogeneity may vary according to the dynamic patterns of climate change at regional or continental scale. The reasons for this may be related to non-climatic factors. To understand the mechanisms by which spatial heterogeneity forms, it is necessary to establish the relationships between glacier mass balance and environmental factors related to topography and morphology. In this study, climate, topography,morphology, and other environmental factors are investigated. Geodetector and linear regression analysis were used to explore the driving factors of spatial variability of glacier mass balance in the HMA by using elevation change data during 2000–2016. The results show that the coverage of supraglacial debris is an essential factor affecting the spatial heterogeneity of glacier mass balance, followed by climatic factors and topographic factors, especially the median elevation and slope in the HMA. There are some differences among mountain regions and the explanatory power of climatic factors on the spatial differentiation of glacier mass balance in each mountain region is weak, indicating that climatic background of each mountain region is similar. Therefore, under similar climatic backgrounds, the median elevation and slope are most correlated with glacier mass balance. The interaction of various factors is enhanced, but no unified interaction factor plays a primary role. Topographic and morphological factors also control the spatial heterogeneity of glacier mass balance by influencing its sensitivity to climate change. In conclusion,geodetector method provides an objective framework for revealing the factors controlling glacier mass balance.

No treeline shift despite climate change over the last 70 years

Background:The recent rise in temperature and shifting precipitation regimes threaten ecosystems around the globe to different degrees.Treelines are expected to respond to climate warming by shifting to higher elevations,but it is unclear whether they can track temperature changes.Here,we integrated high-resolution aerial imagery with local climatic and topographic characteristics to study the treeline dynamic from 1945 to 2015 on the semiarid Mediterranean island of Crete,Greece.Results:During the study period,the mean annual temperature at the treeline increased by 0.81℃,while the average precipitation decreased by 170 mm.The treeline is characterized by a diffuse form,with trees growing on steep limestone slopes(>50°)and shallow soils.Moreover,the treeline elevation decreases with increasing distance from the coast and with aspect(south>north).Yet,we found no shift in the treeline over the past 70 years,despite an increase in temperature in all four study sites.However,the treeline elevation correlated strongly with topographic exposure to wind(R^(2)=0.74,p<0.001).Therefore,the temporal lag in treeline response to warming could be explained by a combination of topographic and microclimatic factors,such as the absence of a shelter effect and a decrease in moisture.Conclusion:Although there was no treeline shift over the last 70 years,climate change has already started shifting the treeline altitudinal optimum.Consequently,the lack of climate-mediated migration at the treeline should raise concerns about the threats posed by warming,such as drought damages,and wildfire,especially in the Mediterranean region.Therefore,conservation management should discuss options and needs to support adaptive management.

1998年夏第二阶段梅雨期乌拉尔山阻塞形势的维持(英文)

The 1998 summer-time floods at the Yangtze River basin of China, the severest in last 50 years or so, directly resulted from the abnormal extension of Meiyu (rainy season), which was related to a weak East Asian summer monsoon and persistent anomalies of extratropical circulation. The long persistence of blocking over the Ural Mountains is a conspicuous feature. The physical processes responsible for the prolonged maintenance of this key system are investigated in terms of internal forcing (transient eddy upon basic flow) and external forcing (tropical heating forcing) via diagnosis and numerical experiments in the paper. Using the adjoint method, the location and structure of optimal perturbations favorable for the development and maintenance of Ural blocking are identified, which shows an apparent coincidence with the observed storm track at the eastern Atlantic to Europe sector. The diagnosis of E-vector and the response of baroclinic stationary wave to transient forcing both suggest further that the enhanced transient eddy activity favors the occurrence and maintenance of positive anomalies. The upper-level jet and heat sources (sinks) during that period are calculated, and the results indicate that the anomaly of upper jet and tropical heating is evident. The ensemble forecasting experiments by a GCM, IAP T42L9 show that the anomalous heating over the tropics, especially over the central-western Pacific and Atlantic, favors the formation of positive anomalies of height at the Ural region. Finally, a self-sustain mechanism of positive anomalies through two-way interaction between planetary stationary wave and transient eddy under the stimulation of anomalous tropical heating is proposed.

Energetics of Boreal Wintertime Blocking Highs around the Ural Mountains

Based on the daily Japanese 55-yr reanalysis data,this study analyzes the maintenance mechanism for 53 boreal winter blocking highs around the Ural Mountains(UBHs)during 1958-2018 based on the atmospheric energy budget equations.After decomposing the circulation into background flow,low-frequency anomalies,and high-frequency eddies,it was found that the interaction between the background flow and low-frequency anomalies is conducive to the maintenance of the UBHs.Due to the southwestward gradient in the climatological mean air temperature over the Eurasian continent,it is easy for the air temperature anomalies as well as the wind velocity anomalies in the middle and lower troposphere induced by the UBHs to facilitate the positive conversion of baroclinic energy associated with the background flow into the UBHs.Likewise,the conversion of barotropic energy associated with the background flow is also evident in the upper troposphere,in which the climatological mean westerlies have evident southward gradient to the northwest of Lake Baikal and southwestward gradient over Barents Sea.Note that the conversion of baroclinic energy associated with the background flow is dominant throughout the lifecycle of UBHs,acting as the major contributor to the maintenance of the UBHs.Although transient eddies facilitate maintenance of the UBHs via positive conversion of barotropic energy in the middle and upper troposphere,they hinder the maintenance of UBHs via negative conversion of baroclinic energy in the lower troposphere.The diabatic heating anomalies tend to counteract the local air temperature anomalies in the middle and lower troposphere,which damps the available potential energy of UBHs and acts as a negative contributor to the UBHs.

Determination of berberine in Phellodendron amurense from different sites of Changbai Mountain

Phellodendron amurense has been used for many years as a medical plant in traditional Chinese medicine and has shown great prospect in recent clinical trials for future applications. Berberine is an essential active compound contained in P. amurense. Our objective in this study was to quantify the content of berberine in P.amurense from sites at different elevations on Changbai Mountain. We collected samples of P. amurense from five different elevations on Changbai Mountain. Berberine in samples was extracted by ultrahigh pressure extraction（UPE）. And the quantity was measured by high performance liquid chromatography（HPLC）. First, the optimal HPLC conditions for berberine were identified with satisfactory precision（relative standard deviation, R SD／5.6 %）, good accuracy（relative error, R E／ 3.6 %） and good linear relation（R2= 0.9998） in the range of 6.576–328.8 mg L-1. Second, the combination of UPE and HPLC methods in quantitative analysis of berberine showed high repeatability（R SD= 3.28 %）, reproducibility（R SD= 4.72 %）,stability（R SD／ 1.27 %） and good recovery（99.54 %） for real plant materials. Samples from Heilongjiang Province at the lowest elevation contained the highest amount of berberine.Similarly, the lowest amount of berberine was recorded in samples from Changbai Forest Bureau of Jilin Province collected at the highest elevation in this paper. The proposed UPE–HPLC method is simple, reliable and low-cost for quantitative analysis of berberine. Content of berberine in P.amurense varied significantly by site on Changbai Mountain.

Can a dam type of an alpine lake be derived from lake geometry?A negative result

Glacial lake outburst floods(GLOFs)represent one of the most serious hazard and risk in deglaciating high mountain regions worldwide and the need for GLOF hazard and risk assessment is apparent.As a consequence,numerous region-and nation-wide GLOF assessment studies have been published recently.These studies cover large areas and consider hundreds to thousands of lakes,prioritizing the hazard posed by them.Clearly,certain simplification is required for executing such studies,often resulting in neglecting qualitative characteristics which would need manual assignment.Different lake dam types(e.g.,bedrock-dammed,moraine-dammed)are often not distinguished,despite they control GLOF mechanism(dam overtopping/dam breach)and thus GLOF magnitude.In this study,we explore the potential of easily measurable quantitative characteristics and four ratios to approximate the lake dam type.Our dataset of 851 lakes of the Cordillera Blanca suggests that while variances and means of these characteristics of individual lake types differ significantly(F-test,t-test),value distribution of different geometrical properties can’t be used for the originally proposed purpose along the spectra.The only promising results are obtained for extreme values(selected bins)of the ratios.For instance,the low width to length ratio indicates likely morainedammed lake while the high value of ratio indicating round-shape of the lake indicates increased likelihood of bedrock-dammed lake.Overall,we report a negative result of our experiment since there are negligible differences of relative frequencies in most of the bins along the spectra.

Evaluation of Precipitation Datasets from TRMM Satellite and Down-scaled Reanalysis Products with Bias-correction in Middle Qilian Mountain,China

Accurate estimates of precipitation are fundamental for hydrometeorological and ecohydrological studies,but are more difficult in high mountainous areas because of the high elevation and complex terrain.This study compares and evaluates two kinds of precipitation datasets,the reanalysis product downscaled by the Weather Research and Forecasting(WRF)output,and the satellite product,the Tropical Rainfall Measuring Mission(TRMM)Multisatellite Precipitation Analysis(TMPA)product,as well as their bias-corrected datasets in the Middle Qilian Mountain in Northwest China.Results show that the WRF output with finer resolution perfonns well in both estimating precipitation and hydrological simulation,while the TMPA product is unreliable in high mountainous areas.Moreover,bias-corrected WRF output also performs better than bias-corrected TMPA product.Combined with the previous studies,atmospheric reanalysis datasets are more suitable than the satellite products in high mountainous areas.Climate is more important than altitude for the\falseAlarms'events of the TRMM product.Designed to focus on the tropical areas,the TMPA product mistakes certain meteorological situations for precipitation in subhumid and semiarid areas,thus causing significant"falseAlarms"events and leading to significant overestimations and unreliable performance.Simple linear bias correction method,only removing systematical errors,can significantly improves the accuracy of both the WRF output and the TMPA product in arid high mountainous areas with data scarcity.Evaluated by hydrological simulations,the bias-corrected WRF output is more reliable than the gauge dataset.Thus,data merging of the WRF output and gauge observations would provide more reliable precipitation estimations in arid high mountainous areas.

Spatial differences of ice volume across High Mountain Asia

Advanced knowledge of glacier ice volume is vital for water resource assessment.Previous studies have focused on the estimation of ice volume,but the quantitative understanding of the spatial variability of ice volume across High Mountain regions is currently lacking.Here,we used global-scale ice thickness,debris cover and equilibrium line data to analyse ice-volume differences at various scales across High Mountain Asia(HMA).The results showed that 6.3%of the HMA glaciers are covered by debris,with debris area and volume accounting for 9%and 13.8%of the total glacier area and volume,respectively.An average debris-cover volume ratio of 13%was observed.The spatial distribution of ice volume across the HMA varies considerably from region to region.The ice volume is predominately distributed on north-facing slopes and accounts for approximately 38%of the total.It is very common in Altay and Sayan,East Tian Shan,West Kunlun,East Kunlun and Qilian Shan.Meanwhile,ice volumes in the Himalayas and Hengduan Shan are mainly distributed on the southeast aspect.Relative weight functions showed that glacier area,maximum length and average thickness are closely related to ice volume,with average relative weights of 63.7%,22.5%and 9.8%,respectively.This study is important for the evolution of glacier volume and water resource assessment.

Constructing dataset of classified drainage areas based on surface water-supply patterns in High Mountain Asia

The High Mountain Asia(HMA)region,ranging from the Hindu Kush and Tien Shan in thewest totheHimalaya inthe southwith an altitude between 2000 and 8844 m,holds the largest reservoir of glaciers and snow outside Earth Polar Regions.In the last decades,numerous glaciers and lake areas there have undergone tremendous changes with water redistribution.In order to increase understanding of the pattern of distribution of water resources,and their dynamic changes at the basin scale,a watershed classification based on the water replenishment patterns dataset was constructed.The input dataset are from the Randolph Glacier Inventory V.6.0 and the vector data of rivers and streams.Four datasets were thus obtained:Glacier-fed and Runoff-fed Drainage Area(GRDA),Glacier-fed and Runoff-free Drainage Area(GDA),Glacier-free and Runoff-fed Drainage Area(RDA),and the Glacier-free and Runoff-free Drainage Area(NGRDA),and the numbers of these four types of basins are 87,107,32,and 448 separately.The statistical results show GRDA has the largest surface area,accounting for 82.2%of the total basin area in HMA,mainly in the region of the basin with outflow rivers or streams.Dominated by small basins,the GDA area accounts for the smallest area,only 3.86%and the RDA accounts for 5.62%.For NGRDA,most are with small areas,accounting for 8.32%,and mainly distributes in the closed basin of the Qiangtang Plateau.This dataset provides a fundamental classified data source for research on water resources,climate,ecology,and environment in HMA.The published data are available at https://data.4tu.nl/download/uuid:d07d748f-d10b-4308-9626-199ef05cc9af/and http://www.dx.doi.org/10.11922/sciencedb.923.

Disaster effects of climate change in High Mountain Asia:State of art and scientific challenges Disaster effects of climate change in High Mountain Asia:State of art and scientific challenges

High Mountain Asia(HMA)shows a remarkable warming tendency and divergent trend of regional precipitation with enhanced meteorological extremes.The rapid thawing of the HMA cryosphere may alter the magnitude and frequency of nature hazards.We reviewed the influence of climate change on various types of nature hazards in HMA region,including their phenomena,mechanisms and impacts.It reveals that:1)the occurrences of extreme rainfall,heavy snowfall,and drifting snow hazards are escalating;accelerated ice and snow melting have advanced the onset and increased the magnitude of snowmelt floods;2)due to elevating trigger factors,such as glacier debuttressing and the rapid shift of thermal and hydrological regime of bedrock/snow/ice interface or subsurface,the mass flow hazards including bedrock landslide,snow avalanche,ice-rock avalanches or glacier detachment,and debris flow will become more severe;3)increased active-layer detachment and retrogressive thaw slumps slope failures,thaw settlement and thermokarst lake will damage many important engineering structures and infrastructure in permafrost region;4)multi-hazards cascading hazard in HMA,such as the glacial lake outburst flood(GLOF)and avalanche-induced mass flow may greatly enlarge the destructive power of the primary hazard by amplifying its volume,mobility,and impact force;and 5)enhanced slope instability and sediment supply in the highland areas could impose remote catastrophic impacts upon lowland regions,and threat hydropower security and future water shortage.In future,ongoing thawing of HMA will profoundly weaken the multiple-phase material of bedrock,ice,water,and soil,and enhance activities of nature hazards.Compounding and cascading hazards of high magnitude will prevail in HMA.As the glacier runoff overpasses the peak water,low flow or droughts in lowland areas downstream of glacierized mountain regions will became more frequent and severe.Addressing escalating hazards in the HMA region requires tackling scientific challenges,including understanding multiscale evolution and formation mechanism of HMA hazard-prone systems,coupling thermo‒hydro‒mechanical processes in multi-phase flows,predicting catastrophes arising from extreme weather and climate events,and comprehending how highland hazards propagate to lowlands due to climate change.

Current state and past changes in frozen ground at the Third Pole:A research synthesis

The thermal state of frozen ground and its changes are important for understanding environmental change and supporting related applications to the Earth’s Third Pole,which is a hotspot area for science research.However,challenges remain in data and modelling,meaning that much information is unavailable,especially for the entire Third Pole region.Here,we provided basic statistical data regarding the current state of frozen ground and its changes over the 1960s–2010s across the entire Third Pole by integrating nearly all currently available ground observation data and high-quality spatial data using machine learning models and existing high-quality frozen ground data products.The results show that the current(2000–2018)areal extents of permafrost and seasonally frozen ground in the Third Pole are approximately 1.27×10^(6)km^(2)(1.15×10^(6)to 1.39×10^(6)km^(2))and 2.59×10^(6)km^(2),accounting for 28%and 58%,respectively.The areal extent of permafrost region is approximately 50%(23%–93%)larger than that of permafrost area(land underlain by permafrost),especially in some early maps.The corresponding regional average of the mean annual ground temperature is approximately−1.51℃(−1.75 to−1.27℃)in the permafrost area.The regional average of active layer thickness overlying the permafrost and the maximum frost depth for regions of seasonally frozen ground are 235 cm(233–237 cm)and 92 cm,respectively.From the 1960s to the 2010s,on average,permafrost in the Third Pole warmed at a rate of 0.17℃per decade,which was associated with increases in the maximum thaw depth at a rate of 4.42 cm per decade.The regional average of the maximum frost depth declined at a rate of 2.34 cm per decade over the same period.This synthesis highlights the differences between the two terms(permafrost region and permafrost area)and provides crucial information for frozen ground in the Third Pole with higher accuracy for the scientific community and the public.

Large eddy simulation study of 3D wind field in a complex mountainous area under different boundary conditions

Large eddy simulations generally are used to predict 3D wind field characteristics in complex mountainous areas.Certain simulation boundary conditions,such as the height and length of the computational domain or the characteristics of inflow turbulence,can significantly impact the quality of predictions.In this study,we examined these boundary conditions within the context of the mountainous terrain around a long-span cable-stayed bridge using a wind tunnel experiment.Various sizes of computational domains and turbulent incoming wind velocities were used in large eddy simulations.The results show that when the height of the computational domain is five times greater than the height of the terrain model,there is minimal influence from the top wall on the wind field characteristics in this complex mountainous area.Expanding the length of the wake region of the computational domain has negligible effects on the wind fields.Turbulence in the inlet boundary reduces the length of the wake region on a leeward hill with a low slope,but has less impact on the mean wind velocity of steep hills.