Southern Slopes Of Himalayas Research Articles

Stable isotopes of precipitation in Nepal Himalaya highlight the topographic influence on moisture transport

The Nepal Himalaya is a transition zone for pollutants transport from the South Asia onto the Tibetan Plateau, with the moist convection identified as dominating the chemical composition that would be transported onto the Plateau. Yet little is known regarding the atmospheric water vapor transport over this region, and how the summer monsoon flows would interact with local topography, with traces detectable from ground sample and observations. The stable oxygen and hydrogen isotopes in precipitation (δ18Op and δDp) are important tracers for understanding various hydrological processes. This study reports, for the first time, stable isotope data in daily precipitation at five stations along a north-south transect on the southern slope of Himalaya, with altitudes ranging from 102 m to 5050 m above sea level (a.s.l). The altitude effect of δ18Op across the region of interest is apparent with an altitudinal lapse rate as 0.17‰/100 m. Seasonal trends in δ18Op and δDp show low values during June–September and higher values during October–May at all of the study sites, with the noticeable decrease of δ18Op during summer indicative of the presence of the Indian monsoon over the eastern Nepal Himalaya. The average d-excess values in the summer precipitation increase with altitudes til 3800 m a.s.l before decreasing afterward to 5050 m a.s.l. This corroborates with previous meteorological discovery in the region, and probably confirms the replacement of prevailing westerly by the southerly monsoon flows during summer monsoon season.

A Model-Based Flood Hazard Mapping on the Southern Slope of Himalaya

Originating from the southern slope of Himalaya, the Karnali River poses a high flood risk at downstream regions during the monsoon season (June to September). This paper presents comprehensive hazard mapping and risk assessments in the downstream region of the Karnali River basin for different return-period floods, with the aid of the HEC-RAS (Hydrologic Engineering Center’s River Analysis System). The assessment was conducted on a ~38 km segment of the Karnali River from Chisapani to the Nepal–India border. To perform hydrodynamic simulations, a long-term time series of instantaneous peak discharge records from the Chisapani gauging station was collected. Flooding conditions representing 2-, 5-, 10-, 50-, 100-, 200-, and 1000-year return periods (YRPs) were determined using Gumbel’s distribution. With an estimated peak discharge of up to 29,910 m3/s and the flood depths up to 23 m in the 1000-YRP, the area vulnerable to flooding in the study domain extends into regions on both the east and west banks of the Karnali River. Such flooding in agricultural land poses a high risk to food security, which directly impacts on residents’ livelihoods. Furthermore, the simulated flood in 2014 (equivalent to a 100-YRP) showed a high level of impact on physical infrastructure, affecting 51 schools, 14 health facilities, 2 bus-stops, and an airport. A total of 132 km of rural–urban roads and 22 km of highways were inundated during the flood. In summary, this study can support in future planning and decision-making for improved water resources management and development of flood control plans on the southern slope of Himalaya.

A new synonym of Ptilagrostis yadongensis and a new record of Stipa bhutanica to the flora of China (Poaceae)

Ptilagrostis Grisebach (1852: 447) is a small genus of the grass family, including approximately 11 species (Wu & Phillips 2006, Barkworth 2007). It occurs in both Asia and North America with about eight species distributed in Qinghai-Tibet Plateau, its diversity center. Ptilagrostis yadongensis Keng & Tang (1985: 44) is one of the species that occurs in this region, which was described based on materials from Yadong, China, the southern slope of Himalayas. The paper was published in a Chinese journal, viz. Journal of Southwest Agriculural University, and had not been noticed until 2005 (Peterson et al. 2005, Wu & Phillips 2006). The author pointed out that P. yadongensis is distinguished from its morphological close, Ptilagrostis concinna (Hooker 1897: 230) Roshevitz (1934: 75) by linear panicles with fewer spikelets, longer and unequal glumes, and shorter and glabrous anthers.

Sources and environmental processes of polycyclic aromatic hydrocarbons and mercury along a southern slope of the Central Himalayas, Nepal.

Semi-volatile pollutants can undergo long-range atmospheric transport from low-altitude source regions to high-altitude regions and then accumulate in surface matrices (soil and plants). The Himalayas is the highest mountain range worldwide, but there have been limited studies on the source, transport, and deposition of polycyclic aromatic hydrocarbons (PAHs) and mercury (Hg) in the region. In this study, atmospheric PAHs, and the PAHs and Hg in soil and foliage were determined along a transect on a southern slope of the Himalayas, Nepal. The study showed anthropogenic emissions of PAHs and Hg occurred in the lowland areas of Nepal, and upslope transport to the high-altitude regions happened for both pollutants. During the upslope transport, forest filter effect and snow scavenging may be the important factors that enhance the deposition of PAHs, contributing to the negative pattern between concentrations of PAHs and altitudes. On the contrary, more Hg accumulated in the high Himalayas, relating to the enhanced deposition in the high altitude caused by the higher input from upper atmosphere. Graphical abstract Distribution and environmental processes of PAHs and Hg along the southern slope of Himalayan mountain.

Combining the least cost path method with population genetic data and species distribution models to identify landscape connectivity during the late Quaternary in Himalayan hemlock.

Himalayan hemlock (Tsuga dumosa) experienced a recolonization event during the Quaternary period; however, the specific dispersal routes are remain unknown. Recently, the least cost path (LCP) calculation coupled with population genetic data and species distribution models has been applied to reveal the landscape connectivity. In this study, we utilized the categorical LCP method, combining species distribution of three periods (the last interglacial, the last glacial maximum, and the current period) and locality with shared chloroplast, mitochondrial, and nuclear haplotypes, to identify the possible dispersal routes of T. dumosa in the late Quaternary. Then, both a coalescent estimate of migration rates among regional groups and establishment of genetic divergence pattern were conducted. After those analyses, we found that the species generally migrated along the southern slope of Himalaya across time periods and genomic makers, and higher degree of dispersal was in the present and mtDNA haplotype. Furthermore, the direction of range shifts and strong level of gene flow also imply the existence of Himalayan dispersal path, and low area of genetic divergence pattern suggests that there are not any obvious barriers against the dispersal pathway. Above all, we inferred that a dispersal route along the Himalaya Mountains could exist, which is an important supplement for the evolutionary history of T. dumosa. Finally, we believed that this integrative genetic and geospatial method would bring new implications for the evolutionary process and conservation priority of species in the Tibetan Plateau.

Spatial-Temporal Distribution and General Circulation of Heavy Snow over Tibet Plateau in 1980-2000

Based on daily precipitation and snow cover data over Tibet Plateau from 1980 to 2010,the spatial and temporal distribution characteristics,inter-annual variation of heavy snowfall are analyzed. The results show that: There are two high frequent areas,southern slope of Himalayas and northern Tibet. The heavy snowfall happens through the whole year and has bimodal the seasonal distribution,first peak is from March to May and second peak is October. Heavy snowfall processes exhibit an obvious decrease which is about 3. 8 times per 10 years during recent 31 years. The general circulations of heavy snowfall are studied through 48 typical example based on NCEP /NCAR daily geopotential height and wind field reanalysis data. The five main general circulation models are defined named Indian low model which is the main model from October to December,south-north troughs model which is the main model in February and second model in March,Balkhash Lake low model which is the main model in January,Iran high model which is the main model in March and plateau vortex /shear line model which is the main model in April. The southern trough plays the important role in all of the models.

Climatic variation and runoff from partially-glacierised Himalayan tributary basins of the Ganges

Climate records for locations across the southern slope of the Himalaya between 77°E and 91°E were selected together with discharge measurements from gauging stations on rivers draining partially-glacierised basins tributary to the Ganges, with a view to assessing impacts of climatic fluctuations on year-to-year variations of runoff during a sustained period of glacier decline. The aims were to describe temporal patterns of variation of glaciologically- and hydrologically-relevant climatic variables and of river flows from basins with differing percentages of ice-cover. Monthly precipitation and air temperature records, starting in the mid-nineteenth century at high elevation sites and minimising data gaps, were selected from stations in the Global Historical Climatology Network and CRUTEM3. Discharge data availability was limited to post 1960 for stations in Nepal and at Khab in the adjacent Sutlej basin. Strengths of climate–runoff relationships were assessed by correlation between overlapping portions of annual data records. Summer monsoon precipitation dominates runoff across the central Himalaya. Flow in tributaries of the Ganges in Nepal fluctuated from year to year but the general background level of flow was usually maintained from the 1960s to 2000s. Flow in the Sutlej, however, declined by 32% between the 1970s and 1990s, reflecting substantially reduced summer precipitation. Over the north-west Ganges–upper Sutlej area, monsoon precipitation declined by 30–40% from the 1960s to 2000s. Mean May–September air temperatures along the southern slope of the central Himalayas dipped from the 1960s, after a long period of slow warming or sustained temperatures, before rising rapidly from the mid-1970s so that in the 2000s summer air temperatures reached those achieved in earlier warmer periods. There are few measurements of runoff from highly-glacierised Himalayan headwater basins; runoff from one of which, Langtang Khola, was less than that of the monsoon-dominated Narayani river, in which basin Langtang is nested.

Amount and temperature effects responsible for precipitation isotope variation in the southern slope of Himalayas

Seasonal variation of stable isotopes in precipitation of Kathmandu Valley on the southern slope of Himalaya was carried out to understand the controlling mechanism of amount and temperature effect on the basis of one year stable isotope data from 2010 to 2011. Highly depleted isotope values in major rainy period are obtained just after the onset of precipitation in summer, which accounts for "amount effect" due to saturation isotopic compositions in high moisture condition, whereas, the higher values in winter are indicative to regional vapors (temperature effect) recycling of various sources. An abrupt depletion of isotope values in mid-June, indicates the onset date of monsoon precipitation, by the replacement of winter air mass with southern monsoon. Thus, precipitation isotopes are a tool revealing the onset date of summer monsoon and temporal features of variability, in local and regional monsoons precipitations. A comparison of long term monthly values of δ 18 O, temperature, and precipitation with GNIP δ 18 O data shows the temporal variations of stable isotopes are mostly controlled by amount and temperature effects. During summer monsoon, the amount effects are stronger for high values of precipitation (R=0.7) and altitude effect appears for low moisture in late rainy season, thus from December to June (winter to pre-monsoon) the controlling features of isotopes remains under the temperature effect. A temporal rate of temperature effect is derived as 0.04‰ per year which indicates a dry signal of atmospheric condition and a temperature relation δ 18 O=(0.371±0.08)T+(0.156±0.05) is obtained from this analysis. The meteoric water lines of Kathmandu before and after monsoon onset of 2011, are found as δD=(4.36±0.3)δ 18 O+(15.66±1.2) and δD=(6.91±0.2)δ 18 O (7.92±2.26) from lab samples result, and δD=9.2δ 18 O+11.725 and δD=8.53δ 18 O+16.65 from GNIP data, which lacks the consistency both for slopes and intercepts values for the study period. The mean lapse rate values of δ 18 O and δD

Assessment of erythemal UV level in Nepal based on solar UV estimates from total ozone mapping spectrometer

Nepal lies on the southern slope of Himalaya in Asia. In a width ranging between 15150 and 250 km, the altitude varies greatly from about 100 m at its southern border to a maximum of 8848 min the northern part. Like the variation in altitude, climatic condition varies quite a lot. Long-term monthly mean erythemal UV daily dose values for Nepal are evaluated using Total Ozone Mapping Spectrometer (TOMS) estimation from the time of its overpass between 1996 and 2003 The results are presented as summer and winter maps of mean UV levels in each satellite grid. The mean winter erythemal UV daily dose ranges between 2.1 and 3.6 kJ mt−2 whereas summer values are found to lie between 4.6 and 9.7 kJ mt−2. The altitude variation increases the UV levels by about 0.2 kJ km−1 in winter months, and 0.9 kJ km−1 in summer. A multiyear monthly average erythemal daily dose in most of the areas shows that the summer value is about three times higher than that in winter. Although year-to-year variation is not pronounced in high- and mid-elevation regions, UV levels seemed to decrease from 1997 to 2002 in the southern part of the country in the low elevation region by about 5.35%. Due to the combined effects of the altitude, low ozone concentration in the troposphere, and thin air, surface UV radiation at higher altitudes is found to be higher than in the surrounding regions.

Genetic Diversity and Geographical Differentiation in Asian Common Wheat (Triticum aestivum L.), Revealed by the Analysis of Peroxidase and Esterase Isozymes

Genetic structure of Asian wheat (Tritium aestivum L.) was investigated by the analysis of two isozymes, using 648 wheat landraces. Gene diversity over all populations was 0.254, and the trend of an eastward decline was observed. By cluster analysis and principal co-ordinate analysis based on genetic distance among populations, thirty-three populations were classified into six clusters, and it was indicated that Asian wheat could be divided into at least three lineages. The first lineage of wheat consisted of populations from Turkey to Sichuan (China), suggesting the spread of wheat to southwest China through the ancient Myanmar route. Wheat populations introduced to China through this route were mostly of the red-grain type, and it was considered that wheat adapted to humid and rather hot condition in southern slope of Himalaya had been selected and introduced to China. The second lineage comprised of populations from the areas along the so-called “Silk Road”. Wheat is commonly cultivated under dry and cold condition in these areas, and was characterized by the frequent distribution of white-grain type. The third lineage contained populations from the coastal area of China and Korea, and genetic relationship with the second lineage was suggested. The result of the present study indicated that Asian wheat is genetically and geographically differentiated, and that different types of genetic resources could be found depending on the growing condition and the lineage of wheat populations.