Himalayan Valleys Research Articles

Measuring the Paradigm Shift in Ecological Services in the Mountainous Urban and Peri-Urban Systems of the Himalaya

In the present study, an attempt has been made to understand the dynamics in ecological demand and supply in the mountainous urban systems of Himalayas using spatial approach during the three decades. The study discusses the spatio-temporal dynamics of urban ecological services (UES) by investigating the pattern of demand and supply patches in the major mountainous urban systems of the Himalayas during the period of 1991-2018. The demand patch (135 %) in the mountainous urban systems of the Himalayas has increased significantly in contrast to a serious decline in the supply patch (-24 %) over the last three decades (1991-2018). The city-scale comparative study indicated Srinagar (80.37 km 2 ) and Kathmandu (51.82) exhibited higher growth in the demand patch in contrast to Gangtok (3.52 km 2 ), which observed comparatively lower growth for the same. On the contrary, the supply patches observed higher depletion in Srinagar (-68.03 km 2 ) and Kathmandu (-54.66 km 2 ) while lower in Gangtok (3.52 km 2 ). However, the intensity of rate of change of demand patch was higher in Srinagar (181.69 %), Shimla (163.04 %) and Itanagar (153.75 %), and comparatively lower in Gangtok (71.84 %) whereas the intensity of the same for supply patch was in higher in Kathmandu (-57.48 %), and lower in Shimla (-12.26 %) and Gangtok (-7.66 %). Significant changes in ecological services, particularly in cities such as Srinagar and Kathmandu, lead to a loss of heterogeneity and wellbeing in urban ecosystems. The cities in Himalayan valleys (Srinagar, Dehradun and Kathmandu) exhibited severe decline in the supply patch and significant rise of demand patch in especially the peri-urban areas followed by the saturation of urban regions. Also, the city on ridges (Shimla, Gangtok and Thimphu) showed moderate growth of demand patch in the urban regions and insignificant growth in the peri-urban regions. As a result, the supply patch exhibited lower depletion in both urban and peri-urban regions. For a robust and sustainable urban system in the Himalayas, the study highlights the implementation of contingent policies combined with resilience methods, particularly in urban and peri-urban areas.

Detection and potential early warning of catastrophic flow events with regional seismic networks.

Early warning is a critical potential tool for mitigating the impacts of large mass wasting and flood events, a major hazard in the Himalaya. We used data from a dense seismic network in Uttarakhand, India, to detect and track a fatal rockslide to mass flow to flood cascade and examine the potential for regional networks to provide early warning for extreme flow events. Detection limits of the 7 February 2021 event depend on the nature of the active process and on the anthropogenic and environmental seismic noise levels at each station. With the existing network, a seismic monitoring system could have detected all event phases from up to 100 kilometers and provided downstream warnings within minutes of event initiation.

Himalaje Sikkimu własnością ludu Lepcza

Lepchas are an indigenous people inhabiting the foothills of the eastern Himalaya. Their myths and narratives provide evidence that they belong to this land, and had not migrated from any other region. Presently the Lepchas reside in remote Himalayan valleys, where they were gradually driven by successive waves of immigrants from Tibet, Nepal and West Bengal. Lepchas are intrinsically devoted to nature. The rivers, lakes, rocks, forests and all animals seem to be sacred to them. They worship the Himalayan peaks towering over their villages. Every clan has his own sacred mountain and lake. The most important goddess is the mighty eight-thousander peak of Kangchenjunga that is clearly visible from every Lepcha village. Lepchas believe that their ancestors were created from the snows of the Kangchenjunga. Now, they are living together with gods in the Mayel Lyang — the mythical paradise hidden somewhere on the slopes of the mountain, inaccessible for mortal beings. Over the generations, the Lepchas have accumulated an extraordinary amount of knowledge about the climate, meteorological phenomena, geography of the region, and agriculture on steep slopes. These people fulfil their needs with natural resources as well as the help of hard work, and have great care for nature. Lepchas know all the animals and wildly growing plants there, and their rich language has names for even the smallest of them. The most impressive is their adaptation to life in extremely difficult geographic and climatic conditions with the constant risk of earthquakes, floods and landslides caused by heavy rainfalls of the monsoon season. Their farms are small and modest, but well adapted to those threats. Family and clan ties are very strong. They help each other with houses construction, sickness care, and agricultural harvest. Lepchas do not care for material goods and despite extremely difficult conditions they are happy and content with their life. Their attitude towards life may be an inspiration for us, inhabitants of the “first world”, addicted to consumerism and materialistic values.

Chemical composition and radiative forcing of atmospheric aerosols over the high-altitude Western Himalayas of India

Aerosol behavior over the Himalayas plays an important role in the regional climate of South Asia. Previous studies at high-altitude observatories have provided evidence of the impact of long-range transport of pollutants from the Indo-Gangetic Plain (IGP). However, little information exists for the valley areas in the high Himalayas where significant local anthropogenic emissions can act as additional sources of short-living climate forcers and pollutants. The valley areas host most economic activities based on agriculture, forestry, and pilgrimage during every summer season. We report here first measurements at a valley site at ~2600 m a.s.l. on the trek to the Gangotri glacier (Gaumukh), in the Western Himalayas, where local infrastructures for atmospheric measurements are absent. The study comprised short-term measurement of aerosols, chemical characterization, and estimation of aerosol radiative forcing (ARF) during the winter and summer periods (2015-2016). The particulate matter mass concentrations were observed to be higher than the permissible limit during the summer campaigns. We obtained clear evidence of the impact of local anthropogenic sources: particulate nitrate is associated with coarse aerosol particles, the black carbon (BC) mass fraction appears undiluted with respect to measurements performed in the lower Himalayas, and in winter, both BC and sulfate concentrations in the valley site are well above the background levels reported from literature studies for mountain peaks. Finally, high concentrations of trace metals such as copper point to anthropogenic activities, including combustion and agriculture. While most studies in the Himalayas have addressed pollution in the high Himalayas in terms of transport from IGP, our study provides clear evidence that local sources cannot be overlooked over the high-altitude Himalayas. The estimated direct clear-sky ARF was estimated to be in the range of -0.1 to +1.6 W m-2, with significant heating in the atmosphere over the high-altitude Himalayan study site. These results indicate the need to establish systematic aerosol monitoring activities in the high Himalayan valleys.

Future Food Sustainability Can Be Traced Back into Local People’s Socio-Cultural Roots in Uttarakhand Himalaya, India

Sustainable food system ensures adequate and safe food supply in an eco-friendly manner. We assessed food sustainability perception and practices of local community through structured interviews in sub-alpine settlements of Uttarakhand Himalaya. Major perceived challenges towards food sustainability were identified using Rank-Based Quotient analysis. Association with various socio-demographic factors (e.g., age, gender, education, socio-economy, and socio-culture) was tested. An overall neutral perception (mean score 2.9) and moderately sustainable practices (mean score 3.1) were observed. Respondents with higher socio-cultural score showed more sustainable food sourcing practices and more positive social and economic sustainability perception, as well as higher participatory willingness. Female respondents were more dependent on sustainable food sources than the males. Education level influenced food quality choice. People identified higher food production cost as major economic constraint; while small landholdings and labor migration were main social challenges. Land and water management issues and climate uncertainty were the major environmental constraints. Socio-cultural exposure played significant role in ranking these sustainability constraints. We encourage direct involvement of socio-culturally active people and conducting extensive outreach programs for future sustainable local food system in vulnerable Himalayan valleys.

Physicochemical properties of irrigation water in western Himalayas, Pakistan

Abstract Appropriate irrigation water quality is essential for maintaining soil properties. This study investigates numerous physicochemical properties of irrigation water in three Himalayan valleys in northern Pakistan, receiving water from different sources. A total of 36 samples (3 replicates from four points at each site) were randomly collected and analyzed following standard laboratory techniques. The results revealed that most of the physicochemical parameters were within the permissible limits as specified by FAO, USEPA, and WWF for agriculture water. However, the total dissolved solids, potassium, mercury, nickel, and cadmium were found beyond the recommended ranges. Analysis of variance indicated that the mean values of various constituents differed significantly across the sources. Among the water sources, the mix of spring and glacial meltwater was found to contain maximum parameters within the permissible limits. The study recommends further investigating the implications of the existing water quality parameters on crop productivity and human health.

Geo-environmental consequences of obstructing the Bhagirathi River, Uttarakhand Himalaya, India

The Bhagirathi Valley is investigated to understand the impact of various barrages and dams on natural river flow. The multiple barrages and dams in the valley (downstream of the Bhatwari Village) have obstructed/disrupted natural flow of the river which has adversely impacted geomorphological and ecological functions of the river. Besides, it is observed that during and after the implementation of the hydropower projects, the terrain stability was severely affected due to creation of fresh landslide zones, destruction of forest and rural infrastructures including the marginal agricultural lands. The study observes that lack of detailed geological, geomorphological and ecological investigation prior to the execution of the hydropower projects led to the terrain instability. Further, dearth of detailed scientific studies was responsible for the lack of comprehensive engineering/bioengineering measures and catchment area treatment plans as also the measures for reservoir rim slope stability. Taking cognizance from the Bhagirathi valley, present study calls for a detailed multidisciplinary study in the Himalayan valleys where the rivers are likely to get impounded for harnessing hydropower.

Seroprevalence and risk factors of hepatitis B virus infection in tribal population of Himalayan district Lahaul and Spiti, India

ABSTRACTHepatitis B virus (HBV) infection is an important health issue across the world. With 4% to 7% prevalence of HBV, India is designated as an intermediate endemic country. However, HBV prevalence is significantly high in some pockets of the country, especially among tribal populations. HBV prevalence and associated risk factors in residents of far-flung two Himalayan valleys, Lahaul and Spiti of Himachal Pradesh (HP), were estimated. This was a community-based cross-sectional study. Blood samples were collected and tested for the presence of hepatitis B surface antigen (HBsAg) using ELISA. Data was collected in a predesigned semi-structured format. Univariate and multivariate analyses of risk factors were done using software SPSS 25. Samples from 1,327 individuals residing in 32 villages were tested, of these 141 (10.6%) were found positive for HBsAg. High prevalence (17.2%) of HBV was recorded in Spiti valley but not in Lahaul valley (3.1%). Both sexes were equally affected. Positivity was higher in adults than in children. High risk sexual behavior (OR = 2.0; 95% CI: 1.1–3.6), having an HBV positive person in the family (OR = 2.4; 95% CI: 1.4–4.3), being a student (OR: 11.2; 95% CI 3.9–32.1) and preacher (OR = 9.0; 95% CI: 3.6–22.4) were the most prominent risk factors associated with HBsAg positivity. Mass immunization for HBV along with information, education, communication and behavior change communication for curtailing risk behavior for avoiding risk factors is essential in the area.

Transport of regional pollutants through a remote trans-Himalayan valley in Nepal

Abstract. Anthropogenic emissions from the combustion of fossil fuels and biomass in Asia have increased in recent years. High concentrations of reactive trace gases and light-absorbing and light-scattering particles from these sources form persistent haze layers, also known as atmospheric brown clouds, over the Indo–Gangetic plains (IGP) from December through early June. Models and satellite imagery suggest that strong wind systems within deep Himalayan valleys are major pathways by which pollutants from the IGP are transported to the higher Himalaya. However, observational evidence of the transport of polluted air masses through Himalayan valleys has been lacking to date. To evaluate this pathway, we measured black carbon (BC), ozone (O3), and associated meteorological conditions within the Kali Gandaki Valley (KGV), Nepal, from January 2013 to July 2015. BC and O3 varied over both diurnal and seasonal cycles. Relative to nighttime, mean BC and O3 concentrations within the valley were higher during daytime when the up-valley flow (average velocity of 17 m s−1) dominated. BC and O3 concentrations also varied seasonally with minima during the monsoon season (July to September). Concentrations of both species subsequently increased post-monsoon and peaked during March to May. Average concentrations for O3 during the seasonally representative months of April, August, and November were 41.7, 24.5, and 29.4 ppbv, respectively, while the corresponding BC concentrations were 1.17, 0.24, and 1.01 µg m−3, respectively. Up-valley fluxes of BC were significantly greater than down-valley fluxes during all seasons. In addition, frequent episodes of BC concentrations 2–3 times higher than average persisted from several days to a week during non-monsoon months. Our observations of increases in BC concentration and fluxes in the valley, particularly during pre-monsoon, provide evidence that trans-Himalayan valleys are important conduits for transport of pollutants from the IGP to the higher Himalaya.

Field study of the building physics properties of common building types in the Inner Himalayan valleys of Bhutan

Traditionally, buildings in the Inner Himalayan valleys of Bhutan were constructed from rammed earth in the western regions and quarry stone in the central and eastern regions. Whilst basic architectural design elements have been retained, the construction methods have however changed over recent decades alongside expectations for indoor thermal comfort. Nevertheless, despite the need for space heating, thermal building performance remains largely unknown. Furthermore, no dedicated climate data is available for building performance assessments. This paper establishes such climatological information for the capital Thimphu and presents an investigation of building physics properties of traditional and contemporary building types. In a one month field study 10 buildings were surveyed, looking at building air tightness, indoor climate, wall U-values and water absorption of typical wall construction materials. The findings highlight comparably high wall U-values of 1.0 to 1.5W/m²K for both current and historic constructions. Furthermore, air tightness tests show that, due to poorly sealed joints between construction elements, windows and doors, many buildings have high infiltration rates, reaching up to 5 air changes per hour. However, the results also indicate an indoor climate moderating effect of more traditional earth construction techniques. Based on these survey findings basic improvements are being suggested.

Reordering a Border Space: Relief, rehabilitation, and nation-building in northeastern India after the 1950 Assam earthquake

AbstractOn 15 August 1950, just as India was celebrating its third independence anniversary, an earthquake of 8.6 magnitude struck the remote northeastern state of Assam and its surrounding borderlands. Rivers burst their banks and landslides blocked Himalayan valleys, destroying towns, villages, roads, fields, and tea gardens in their wake. Beyond the disaster's shattering impact on the physical geography of the region, this article explores how it participated in another reconfiguration—that of Assam's place within India's political geography and national imaginary. The Indian public had hitherto known very little about India's remote ‘northeast frontier’; the cataclysm and subsequent relief measures served to carve out a space for it on Indian mental maps. Simultaneously, by forcing a large-scale encounter between Indian authorities and the people of the scarcely controlled eastern Himalayas, post-earthquake relief and rehabilitation led to unprecedented state expansion in this newly strategic borderland. Yet in the same breath, the aftermath of the disaster fuelled stereotypes about Assam and its hinterland that would eventually further their marginality within India and undermine their continued unity. The crystallization of Assam's image as a place irreducibly subject to the whims of nature and, more importantly, incapable of taking care of itself (and hence, of its highland dependencies), would poison centre–state relations for decades to come. Imperfect and contradictory, the reordering of this border space from a colonial frontier to a component of independent India's national space did not end marginality, but instead reinforced it.

God does not play dice: Looking back from modern laboratories to the Himalayan valleys.

God does not play dice: Looking back from modern laboratories to the Himalayan valleys.

Cardiovascular function in healthy Himalayan high-altitude dwellers

BackgroundResidents of the Himalayan valleys uniquely adapted to their hypoxic environment in terms of pulmonary vasculature, but their systemic vascular function is still largely unexplored. The aim of the study was to investigate vascular function and structure in rural Sherpa population, permanently living at high altitude in Nepal (HA), in comparison with control Caucasian subjects (C) living at sea level. Methods and results95 HA and 64 C were enrolled. Cardiac ultrasound, flow-mediated dilation (FMD) of the brachial artery, carotid geometry and stiffness, and aortic pulse wave velocity (PWV) were performed. The same protocol was repeated in 11 HA with reduced FMD, after 1-h 100% O2 administration.HA presented lower FMD (5.18 ± 3.10 vs. 6.44 ± 2.91%, p = 0.02) and hyperemic velocity than C (0.61 ± 0.24 vs. 0.75 ± 0.28 m/s, p = 0.008), while systolic pulmonary pressure was higher (29.4 ± 5.5 vs. 23.6 ± 4.8 mmHg, p < 0.0001). In multiple regression analysis performed in HA, hyperemic velocity remained an independent predictor of FMD, after adjustment for baseline brachial artery diameter, room temperature and pulse pressure, explaining 8.7% of its variance. On the contrary, in C brachial artery diameter remained the only independent predictor of FMD, after adjustment for confounders. HA presented also lower carotid IMT than C (0.509 ± 0.121 vs. 0.576 ± 0.122 mm, p < 0.0001), higher diameter (6.98 ± 1.07 vs. 6.81 ± 0.85 mm, p = 0.004 adjusted for body surface area) and circumferential wall stress (67.6 ± 13.1 vs. 56.4 ± 16.0 kPa, p < 0.0001), while PWV was similar. O2 administration did not modify vascular variables. ConclusionsHA exhibit reduced NO-mediated dilation in the brachial artery, which is associated to reduced hyperemic response, indicating microcirculatory dysfunction. A peculiar carotid phenotype, characterized by reduced IMT and enlarged diameter, was also found.

Evolution of valley-fill terraces in the Alaknanda Valley, NW Himalaya: Its implication on river response studies

The present study attempts to understand the importance of place and local factors in the process of valley filling in an active mountain belt. The accumulation of sediments in a valley stretch depends upon the relationship between sediment carried from upstream by the main river entering into the stretch (qi), locally derived sediments (i.e., from local streams (qt), hillslopes (qh), and glacial and periglacial processes (qg)), and sediment exiting that stretch (qo); these are in turn governed by other processes like tectonic activity, intensity of precipitation, and lithology.As an example a valley stretch in the NW Himalaya is chosen in the Alaknanda River, one of the two uppermost tributaries of the Ganga River. This stretch is called as Pipalkoti Valley after the name of the main town; it is located close to the Main Central Thrust (MCT) and falls in the zone of orographic precipitation. Detailed geomorphic mapping reveals four surfaces and two terraces. Three debris-flow surfaces suggest their deposition by local mass flows and stream flows with very small contributions from the Alaknanda River. Terrace T2 occurs as a strath in some parts and is made up of fluvial and lacustrine sediments in others. The presence of lacustrine sediments suggests local damming of the river. Thick fluvial sediment is deposited in stretches of the rivers where it becomes wide due to the joining of a tributary. Synsedimentary deformation has been noted indicating that tectonic activity has affected sedimentation.The results suggest that local processes played a dominant role in the accumulation of sediments in this valley stretch. A model is proposed showing the role of glacial activity, high intensity meteorological events, river width, active faults and landslide damming in the origin of valley-fill deposits of the Pipalkoti Valley. It is concluded that before correlating valley-fill deposits along the lengths of the Himalayan valleys, it is important to evaluate the role of various local processes that have operated in particular stretches.

Potential Effects of Ongoing and Proposed Hydropower Development on Terrestrial Biological Diversity in the Indian Himalaya

Indian Himalayan basins are earmarked for widespread dam building, but aggregate effects of these dams on terrestrial ecosystems are unknown. We mapped distribution of 292 dams (under construction and proposed) and projected effects of these dams on terrestrial ecosystems under different scenarios of land-cover loss. We analyzed land-cover data of the Himalayan valleys, where dams are located. We estimated dam density on fifth- through seventh-order rivers and compared these estimates with current global figures. We used a species-area relation model (SAR) to predict short- and long-term species extinctions driven by deforestation. We used scatter plots and correlation studies to analyze distribution patterns of species and dams and to reveal potential overlap between species-rich areas and dam sites. We investigated effects of disturbance on community structure of undisturbed forests. Nearly 90% of Indian Himalayan valleys would be affected by dam building and 27% of these dams would affect dense forests. Our model projected that 54,117 ha of forests would be submerged and 114,361 ha would be damaged by dam-related activities. A dam density of 0.3247/1000 km(2) would be nearly 62 times greater than current average global figures; the average of 1 dam for every 32 km of river channel would be 1.5 times higher than figures reported for U.S. rivers. Our results show that most dams would be located in species-rich areas of the Himalaya. The SAR model projected that by 2025, deforestation due to dam building would likely result in extinction of 22 angiosperm and 7 vertebrate taxa. Disturbance due to dam building would likely reduce tree species richness by 35%, tree density by 42%, and tree basal cover by 30% in dense forests. These results, combined with relatively weak national environmental impact assessment and implementation, point toward significant loss of species if all proposed dams in the Indian Himalaya are constructed.

Mapping aerosol intrusion in Himalayan valleys using the Moderate Resolution Imaging Spectroradiometer (MODIS) and Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO)

Mapping the spatial and temporal distribution of aerosols along mountain ranges is an important step toward elucidating orographic aerosol–cloud–rainfall interactions. This requires high spatial resolution aerosol observations over complex topography, which are not currently available either from ground-based observing systems or from remote-sensing products. Here, a novel approach is presented that relies on visible channels from MODIS Rapid Response data at 250 m spatial resolution to extract the daytime aerosol run-up (intrusion length and height) from the Indo-Gangetic Plains to the High Himalaya. Intrusion length and height are determined from the intersection of topography with the MODIS-derived aerosol plume using an adaptive object-classification algorithm. The methodology is demonstrated for a case study of the Arun River in eastern Nepal. Results of run-up extraction are examined along with the Total Attenuated Backscatter (Level 1B at 532 nm) from CALIPSO to investigate the regional variability of aerosol. During the pre-monsoon season, CALIPSO nighttime profiles show the presence of a slanted dust layer following the envelope topography. This is consistent with upper level transport of aerosol by north-westerly winds associated with high-frequency dust storms. In the winter, the signal is weaker, and the nighttime elevated aerosol layer is flat and remains below the envelope orography consistent with blocking conditions. For both seasons, the daytime aerosol layer detected from MODIS observations is always below the ridges. This suggests that in addition to seasonal variability governed by synoptic conditions, there is a distinct diurnal cycle in the North–South transport of aerosol between the Himalayas and the IGP. ► High-resolution mapping of aerosol plumes in mountainous regions. ► Aerosol run-up (intrusion length and plume depth) in deep Himalayan valleys. ► Remote-sensing technique using MODIS RR and CALIPSO TBA data. ► Pre-monsoon nocturnal aerosol transport elevated above orography, blocked in winter. ► Diurnal cycle impacted by local sources, governed by mountain-valley circulations.

Atmospheric Brown Clouds in the Himalayas: first two years of continuous observations at the Nepal Climate Observatory-Pyramid (5079 m)

Abstract. This paper provides a detailed description of the atmospheric conditions characterizing the high Himalayas, thanks to continuous observations begun in March 2006 at the Nepal Climate Observatory-Pyramid (NCO-P) located at 5079 m a.s.l. on the southern foothills of Mt. Everest, in the framework of ABC-UNEP and SHARE-Ev-K2-CNR projects. The work presents a characterization of meteorological conditions and air-mass circulation at NCO-P during the first two years of activity. The mean values of atmospheric pressure, temperature and wind speed recorded at the site were: 551 hPa, −3.0 °C, 4.7 m s−1, respectively. The highest seasonal values of temperature (1.7 °C) and relative humidity (94%) were registered during the monsoon season, which was also characterized by thick clouds, present in about 80% of the afternoon hours, and by a frequency of cloud-free sky of less than 10%. The lowest temperature and relative humidity seasonal values were registered during winter, −6.3 °C and 22%, respectively, the season being characterised by mainly cloud-free sky conditions and rare thick clouds. The summer monsoon influenced rain precipitation (seasonal mean: 237 mm), while wind was dominated by flows from the bottom of the valley (S–SW) and upper mountain (N–NE). The atmospheric composition at NCO-P has been studied thanks to measurements of black carbon (BC), aerosol scattering coefficient, PM1, coarse particles and ozone. The annual behaviour of the measured parameters shows the highest seasonal values during the pre-monsoon (BC: 316.9 ng m−3, PM1: 3.9 μg m−3, scattering coefficient: 11.9 Mm−1, coarse particles: 0.37 cm−3 and O3: 60.9 ppbv), while the lowest concentrations occurred during the monsoon (BC: 49.6 ng m−3, PM1: 0.6 μg m−3, scattering coefficient: 2.2 Mm−1, and O3: 38.9 ppbv) and, for coarse particles, during the post-monsoon (0.07 cm−3. At NCO-P, the synoptic-scale circulation regimes present three principal contributions: Westerly, South-Westerly and Regional, as shown by the analysis of in-situ meteorological parameters and 5-day LAGRANTO back-trajectories. The influence of the brown cloud (AOD&gt;0.4) extending over Indo–Gangetic Plains up to the Himalayan foothills has been evaluated by analysing the in-situ concentrations of the ABC constituents. This analysis revealed that brown cloud hot spots mainly influence the South Himalayas during the pre-monsoon, in the presence of very high levels of atmospheric compounds (BC: 1974.1 ng m−3, PM1: 23.5 μg m−3, scattering coefficient: 57.7 Mm−1, coarse particles: 0.64 cm−3, O3: 69.2 ppbv, respectively). During this season 20% of the days were characterised by a strong brown cloud influence during the afternoon, leading to a 5-fold increased in the BC and PM1 values, in comparison with seasonal means. Our investigations provide clear evidence that, especially during the pre-monsoon, the southern side of the high Himalayan valleys represent a "direct channel" able to transport brown cloud pollutants up to 5000 m a.s.l., where the pristine atmospheric composition can be strongly influenced.

Aerosol optical properties and radiative forcing in the high Himalaya based on measurements at the Nepal Climate Observatory-Pyramid site (5079 m a.s.l.)

Abstract. Intense anthropogenic emissions over the Indian sub-continent lead to the formation of layers of particulate pollution that can be transported to the high altitude regions of the Himalaya-Hindu-Kush (HKH). Aerosol particles contain a substantial fraction of strongly absorbing material, including black carbon (BC), organic compounds (OC), and dust all of which can contribute to atmospheric warming, in addition to greenhouse gases. Using a 3-year record of continuous measurements of aerosol optical properties, we present a time series of key climate relevant aerosol properties including the aerosol absorption (σap) and scattering (σsp) coefficients as well as the single-scattering albedo (w0). Results of this investigation show substantial seasonal variability of these properties, with long range transport during the pre- and post-monsoon seasons and efficient precipitation scavenging of aerosol particles during the monsoon season. The monthly averaged scattering coefficients range from 0.1 Mm−1 (monsoon) to 20 Mm−1 while the average absorption coefficients range from 0.5 Mm−1 to 3.5 Mm−1. Both have their maximum values during the pre-monsoon period (April) and reach a minimum during Monsoon (July–August). This leads to dry w0 values from 0.86 (pre-monsoon) to 0.79 (monsoon) seasons. Significant diurnal variability due to valley wind circulation is also reported. Using aerosol optical depth (AOD) measurements, we calculated the resulting direct local radiative forcing due to aerosols for selected air mass cases. We found that the presence of absorbing particulate material can locally induce an additional top of the atmosphere (TOA) forcing of 10 to 20 W m−2 for the first atmospheric layer (500 m above surface). The TOA positive forcing depends on the presence of snow at the surface, and takes place preferentially during episodes of regional pollution occurring on a very regular basis in the Himalayan valleys. Warming of the first atmospheric layer is paralleled by a substantial decrease of the amount of radiation reaching the surface. The surface forcing is estimated to range from −4 to −20 W m−2 for small-scale regional pollution events and large-scale pollution events, respectively. The calculated surface forcing is also very dependent on surface albedo, with maximum values occurring over a snow-covered surface. Overall, this work presents the first estimates of aerosol direct radiative forcing over the high Himalaya based on in-situ aerosol measurements, and results suggest a TOA forcing significantly greater than the IPCC reported values for green house gases.

Holocene glacier fluctuations and migration of Neolithic yak pastoralists into the high valleys of northwest Bhutan

Here we present geomorphologic, palaeoenvironmental and archaeo-botanical data which elucidate the Late Pleistocene and Holocene glacial history of the high, mountain-locked Himalayan valleys in northwest Bhutan and provide one of the earliest proofs of human activity yet known for the High Himalaya range. In this area, difficult to access, close linkage between climatic change, glacier fluctuations and human migration patterns has been discovered. Glacier systems in the studied area are characterized by avalanching and debris mantled glacier snouts, with the significant local influence of the Indian summer monsoon causing decoupling of glacier responses from temperature changes but supporting the idea of monsoonal forcing. Geomorphologic mapping, together with Optically Stimulated Luminescence (OSL) and radiocarbon dating of ice-proximal sediments, has been used to construct a local glacial chronology. Local ice-stream networks developed during the Early Holocene (ca 10,000–9000 a ago) and during the early part of the Mid Holocene (6710 ± 90–4680 ± 155 cal a BP) at which times there were ice advances of about 5 km from the modern glacier termini. At such times, the intensity of pro- and periglacial processes would have intensified and ice-dammed lakes were probably common as well, rendering human colonization of the high valleys in northwest Bhutan impossible. An abrupt shift to dry climatic conditions on the Tibetan Plateau between 5000 and 4500 a BP coincided with glacial decay and the onset of morphodynamically stable conditions on the broad valley floors of the high valleys in this part of the Himalaya. Palynological data suggest that the sudden disappearance of juniper and rhododendron pollen, the immediate onset of pollen input from cereals (confirmed by detailed SEM analysis) and a clear pattern of over-grazing, trampling and peat deterioration can be linked to human arrival in the valleys at ca 4280 ± 130 cal a BP. Extensive charcoal horizons dating to 4745 ± 250 and 4680 ± 155 cal a BP are interpreted as evidence for human use of fire and forest clearances and agree spatially and temporally with the pollen-based picture. Charcoal occurrences as old as 6710 ± 90 cal a BP might be linked to yet earlier exploration of these Himalayan valleys during phases of low glacial activity. We provide an account of the colonization of these high valleys in response to glacial and monsoonal change and argue that the most likely founder societies come from the Tibetan Plateau, where yak and barley based pastoralism and Neolithic settlements are known to have existed since the Mid Holocene.

Quaternary fans and terraces in the Khumbu Himal south of Mount Everest: their characteristics, age and formation

Large fans and terraces are frequent in the Khumbu Himal within the high Himalayan valleys south of Mt. Everest. These features are composed of massive matrix- and clast-supported diamicts that were formed from both hyperconcentrated flows and coarse-grained debris flows. Cosmogenic radionuclide (CRN) exposure ages for boulders on fans and terraces indicate that periods of fan and terrace formation occurred at c . 16, c . 12, c . 8, c . 4 and c . 1.5 ka, and are broadly coincident with the timing of glaciation in the region. The dating precision is insufficient to resolve whether the surfaces formed before, during or after the correlated glacial advance. However, the sedimentology, and morphostratigraphic and geomorphological relationships suggest that fan and terrace sedimentation in this part of the Himalaya primarily occurs during glacier retreat and is thus paraglacial in origin. Furthermore, modern glacial-lake outburst floods and their associated deposits are common in the Khumbu Himal as the result of glacial retreat during historical times. We therefore suggest that Late Quaternary and Holocene fan and terrace formation and sediment transfer are probably linked to temporal changes in discharge and sediment load caused by glacier oscillations responding to climate change. The timing of major sedimentation events in this region can be correlated with fans and terraces in other parts of the Himalaya, suggesting that major sedimentation throughout the Himalaya is synchronous and tied to regional climatic oscillations. Bedrock incision rates calculated from strath terrace ages average c . 3.9 mm a −1 , suggesting that the overall rate of incision is set by regional uplift.