An Application of Geospatial Based MCDM Technique to Identify Landslide Susceptibility Zones in the Ragnu Khola River Basin of Darjeeling Himalayan Region, India

Several natural disasters are taking place on the earth, and landslide is one of them. Darjeeling Himalaya is one of the world's young fold mountainous area, often suffering from landslide hazards. Hence, the study identifies the landslide susceptibility zone in the Ragnu Khola river basin of the Darjeeling Himalayan region by applying the geospatial-based MCDM technique. This research's major goal is to identify whether this GIS-based multi-criteria decision-making (MCDM) technique is validated or not for landslide susceptibility zones (LSZ); if validated, then how much manifest for describing the LSZ in the study area. MCDM evaluation applies to determining weight value to integrate different thematic layers of river morphometry like Drainage Diversity (DD) parameters and Relief Diversity (RD) parameters. Both DD and RD have significant impacts on landslide intensity. Hence, both layers are combined using the analytical hierarchy process (AHP) of the MCDM technique for the final LSZ. The final result has been validated by ROC analysis using landslide occurring point data obtained from the Geological Survey of India (GSI). The outcome of the study shows that1.45% and 17.83% areas of the region fall in 'very high' and ‘high' LSZ, which belongs to near Mull Gaon, Sanchal forest, and Alubri basty. Most of the area (47.70%) is observed in 'moderate' LSZ. Only 1.32% and 31.7% are kept in ‘very low’ and ‘low’ LSZ, respectively, through the study area. The description capability of the technique for LSZ is significant as the area under the curve (AUC) is 72.10%. The validation of the study using the frequency density of the landslides (FDL) also indicates the 'very high' LSZ is associated with the maximum (2.19/km2) FDL. The work will be needful to develop the overall socio-economic condition of such kind of tectonically sensitive region by proper effective planning.

Architecture and Source of Alluvial Fan deposits of the Gish and Lish Rivers, Sikkim-Darjeeling Himalaya, India

The Gish and Lish rivers are flowing through Higher Himalaya, Lesser Himalaya, Sub Himalaya and Quaternary Alluvium of the Sikkim- Darjeeling region. These thrust bounded tectonostratigraphic zones are comprised of different lithologies. Comparative sedimentological studies of the sediments of these rivers were undertaken to understand landforms developed by these rivers and source to sink relationships of these sediments. The Gish River fans are broad and wider as compared to the narrow and linear shaped fans of the Lish River. Textural analysis of these fan sediments revealed high energy conditions of deposition within these rivers. The petrographic analysis of the Gish River sediments shows dominance of Quartz (Qt63%F4% L33%) in the framework components, while the Lithic metamorphic fragments (Lm62% LV0% Ls 38%) show dominance over Lithic sedimentary fragments. This is also supplemented by the dominance of Quartz Polycrystalline grains (Qp62% Lv0% Ls38%) over Lithic sedimentary fractions. The Lish river sediments show dominance of Lithic fragments (Qt39% F2% L59%) in the framework components, while the Lithic sedimentary fragments (Lm44% Lv0% Ls56%) show dominance over lithic metamorphic fragments. This is also supplemented by Lithic sedimentary fractions (Qp41% Lv0% Ls59%) dominance over the Quartz Polycrystalline grains. These results of Quartz dominance in the Gish River sediments indicate higher contribution is from gneissic and metamorphic sources. While, Lithic dominance in the Lish River sediments infers higher contribution from sedimentary and metamorphic sources.

Assessment of the naturalness and anthropogenic transformation of the habitats of small mountain streams in different climate zones

The study compares the quality of the habitats of mountain streams in sections without visible human integration and those permanently transformed by human activity between mountain areas in different climate zones. Three mountain streams with small catchments (10–20 km2) characterized by different natural conditions were selected for the research. The selected streams are Bystrzanka (Beskid Niski, Polish Carpathians), Peshok (Darjeeling Himalaya in India), and Fanshen (Hengduan Shan in China). Field studies were carried out using the British River Habitat Survey (RHS) method. Habitat quality was analyzed based on the following indicators: Habitat Quality Assessment (HQA) and Habitat Modification Score (HMS). The obtained results indicated that sections of mountain streams located in upper catchment areas show greater habitat naturalness in relation to stream sections in lower areas. This results from the greater variety and number of natural hydromorphological elements in streams and the close vicinity of channels. In both upper and lower stream sections, regardless of the degree of naturalness and anthropopressure, the same RHS attributes have the greatest impact on the HQA and HMS values. Similar regularities in the degree of naturalness and anthropogenic modifications of the habitat between the upper and lower reaches of streams can be also expected in other mountain areas, apart from areas not affected by human activities.

Diversity and Distribution of Vascular Epiphytic Flora in Sub-temperate Forests of Darjeeling Himalaya, India

Aims: This communication deals with the diversity and distribution including host species distribution of vascular epiphytes also reflecting its phenological observations. Study Design: Random field survey was carried out in the study site to identify and record the taxa. Host species was identified and vascular epiphytes were noted. Study Site and Duration: The study was conducted in the sub-temperate forests of Darjeeling Himalaya which is a part of the eastern Himalaya hotspot. The zone extends between 1200 to 1850 m amsl representing the amalgamation of both sub-tropical and temperate vegetation. The study was conducted during the year 2018-2019. Methodology: Process of random sampling collection was followed. Host trees with CBH >30 cm were identified and percentage of distribution of epiphytes in the host tree was analyzed and divided into two zones depending on the abundance of epiphytes. Data for the epiphytic plant specimens were collected in the field. Exsiccates were made with the collected voucher specimens and were deposited at the Calcutta University Herbarium (CUH) following the conventional methodology. Study on the taxa are based on their host tree distribution, micro-habitat and phenological status. The location and altitude of the study sites were recorded by global positioning system. Results: A total number of 115 species under 70 genera and 31 families have been identified with 65% other vascular angiosperms (basal angiosperms and eudicots) and 16% monocots. Orchidaceae among the monocots represented 36% with 41 species and 18 genera. Ferns and lycophytes include 25% of the diversity with 29 taxa under 6 families. Most favorable host trees were Ficus auriculata Lour., Ficus neriifolia Sm., Saurauia nepalensis DC., Erythrina variegata L., Macaranga denticulata (Blume) Müll. Arg., Cryptomeria japonica (Thunb. ex L.f.) D. Don and Engelhardia spicata Lechen ex Blume. Conclusion: The other vascular angiosperms preferred wet monsoon for flowering whereas spring season was most favourable for Orchidaceae. Although a healthy number of vascular epiphytes have been identified, a number of threats are still prevailing in the regions which are mostly anthropogenic. Proper collaborative strategies have to be maintained for its conservation.