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Conferences

Conference Papers

European Geosciencs Union (EGU): Vienna, Austria: (April 23 - 28)

2023

Title: Identification of an elevational breakpoint where climatic signal changes for the growth of Larix decidua tree-rings in a glacier-fed river basin in the Swiss Alps.

Abstract: Tree-rings are a valuable proxy for reconstructing past environmental conditions such as climate at annual or intra-annual resolutions. Tree-ring dating has an enormous potential for better understanding climate dynamics under a changing climate. In Alpine regions, changes in climate may well lead to switches between temperature-limitation and precipitation-limitation. However, such changes cannot be separated from local environmental influences such as altitude and aspect. In this study, we applied the standard statistical approaches of dendrochronology to understand climate-growth relationships as a function of elevational gradients to understand how altitude conditions the impacts of climate change impacts on tree growth. For the growth of European Larch (Larix decidua) trees in the Turtmann river basin (2000 m a.m.s.l.), a glacier-fed river basin in the Swiss Alps, located in south-western Switzerland, we find that climate warming is leading to some switching from temperature limitation to precipitation limitation and vice-versa according to altitude. The climate-growth relationship further reveals that the growth of Larix decidua in this river basin is positively correlated with the October and November temperature of the previous year (r= 0.46, a=0.01). Comparing these changes with other tree-ring chronologies from the international tree-ring data bank (ITRDB) for the same species at much lower elevation transects  (e.g. 1500 m and 900 m a.m.s.l) show that the tree growth switches from temperature limitation to precipitation limitation. The growth of Larix decidua for these lower elevation trees correlates positively with the current year June-July precipitation (r= 0.40, a=0.01). A number of factors including differences in micro-climate and the effects of aspect (i.e. north versus south facing) across the elevational gradient are most likely to be responsible for these differences. Therefore, in the context of Swiss Alps where the temperature is rising at more than twice the global average, there is likely a breakpoint where the signal changes from temperature-limitation to precipitation-limitation across the elevational gradient and that climate change is causing this breakpoint to rise with altitude through time.

Tree Rings in Archaeology, Climatology, and Ecology (TRACE): Erlangen, Germany: (May 24 - 27)

2022

Title: Identification of an elevational breakpoint where climatic signal changes for the growth of Larix decidua tree-rings in a glacier-fed river basin in the Swiss Alps.

Abstract: The earlywood and latewood chronologies of the stable oxygen (d18O) and hydrogen (d2H) isotopes derived from tree-rings show a distinctive pattern of intra-annual variations in isotopic compositions in the Turtmänna river basin located in south-western Switzerland. This basin has a high altitudinal range from 4,150 m to 678 m above sea level, with extensive glacier cover above 2,500 m above sea level. An upstream hydropower dam (2,200 m a.s.l) takes off almost all glacial melt, but this is then compensated for by water supply from rainfall and snow melt from un-exploited basins downstream. Without the impact of hydropower we would expect a downstream gradient in the depletion of stable isotopes, which should be reflected in the stable isotope signature of trees. To assess whether or not these trends are seen in the stable isotope records of trees in this catchment, we double-cored a European Larch (Larix Decidua) tree proximal to the river and distal to the river, at a site close to the hydropower dam (site-1), intermediate (site 2) and distal (site-3), as well as a reference tree. The standard chronology after crossdating dated back to 1851 (i.e. 170-years record) shows decreasing growth over the last two decades. Growth was correlated positively with precipitation (r= 0.50), and negatively with temperature (r= 0.30) during the growing season. Results suggest a progressive temporal increase in d18OTR in both earlywood and latewood reflecting a switch to rainfall supply from snow-melt, and to snow-melt from glacier-melt.

EGU: Vienna, Austria: (May 23 - 27)

Title: Use of stable isotope signals from tree rings for tracing combined effects of climate change and
hydropower on glacier-derived Turtmann river basin, Switzerland

Abstract: Stable isotope analyses (e.g. of δ18O, δ2H) combined with the tree-ring dating have enormous potential for tracing freshwater resource availability under changing climate and in the context of the impacts of other human activities. In this study, we analysed the isotopic composition of tree-rings in-combination with the anatomical analysis of the European Larch (Larix Decidua) species from different sites from upstream to downstream along the Turtmänna river in the south-western Switzerland. The results show distinctive pattern of year-to-year tree-ring growth changes from the constructed chronology dated back to 1851 (i.e. 170 years long). A trend of declining growth was observed in the last two decades. Declining growth was correlated (r = 0.50) with declining precipitation and with increasing temperature (r = 0.30) during the growing season (between June to October) of previous and current years. The isotopic analysis shows a constant depletion in δ18O in the trees fed by glacial meltwater close to the river as compared to the trees fed by precipitation distal to the river. Evidence suggests that under climate change, close-to-river trees are becoming more dependent on river-derived water associated with glacier melt and hence upon the impacts of hydropower on instream, water availability.

2021

Swiss Geosciencs Meeting (SGM): Geneva, Switzerland: (November 19 - 20)

Title: Changes in the growth of tree-rings and their water sources in relation to climatic changes in the
Turtmann river basin, Switzerland

Abstract: Climate change has important impacts both on water-related risks (e.g., flooding) and water-related resources, notably the reduction of glacial meltwater in mountain regions including Alpine catchments. Water-related risks (e.g. extreme events) can be identified by detecting the unexpected growth changes in tree-rings (often called pointer years), whereas water-related resources (e.g. changing water sources) can be traced by isotopic compositions analysed for cellulose extracted from tree-rings.  A pilot study in the Turtmänna river catchment (110 km2), south-western Switzerland, indicates distinctive patterns of climate change via the tree-rings in two different species. The tree-ring width (TRW) chronologies from cores of Larix decidua (larch) and Picea abies (spruce) collected from four different zones (at 3 km intervals) along the 18 km long Turtmänna river, downstream of the Turtmannsee reservoir, shows that in the last two decades (2000-2020) the trees have experienced a steady decline in their growth (approx. 50%) with higher fluctuations in year-to-year growth that correlate strongly with recent climate warming. The longest TRW chronology was constructed for 146 years (dated back to 1874) in site-4, which demarcates a strong positive correlation with reference chronology (Gleichläufigkeit or GLK = 73%, p < 0.001). Furthermore, the results also provide evidence that the growth of tree-rings even of the same species within the same zone differs significantly from trees next to the river compared to the trees that are more distal to the river. This supports the hypothesis that the growth of the trees that have direct access to the proglacial streams likely depend on glacier-meltwater induced runoff, whereas the trees that are distal to the river predominantly depend on groundwater accessibility that may decrease with decreasing amounts of precipitation. In comparison to picea abies, larix decidua shows higher sensitivity to regional climate fluctuations and some years of unexpected growth changes are well correlated with the years of rockfall events. However, this research work is currently at a preliminary stage. Further work will trace water sources by trees that are even more distal to the river and hence further assess the impacts of water intake from the stream on the tree-ring growth in the Turtmänna river catchment.

2019

International Conference on Water and Flood Management (ICWFM): Dhaka, Bangladesh: (March 02 - 04) [details​]

Title: A GIS-based Monte Carlo Least Cost Path (MC-LCP) method for assessing the outburst flood risk from Phunri Glacial Lake, Sikkim Himalayas, India

Abstract: Glacial Lake Outburst Floods (GLOFs) are one of the most potent natural hazards in the Himalayan region, posing significant threat to the millions residing downstream from their occurrence sites along the region’s foothills and extensively threatening built infrastructure and livelihoods. This paper examines the efficacy of a GIS-based Monte Carlo Least Cost Path (MC-LCP) method for assessing the GLOF induced risks from the Phunri Lake, which is located in the source region of the Teesta River, an important right bank tributary of the River Brahmaputra located at in the eastern Indian state of Sikkim. We analysed high resolution multispectral satellite imageries from 2000 to 2018 and digital elevation model for lake inventories,and modelled potential GLOF risk downstream of this lake using GAPHAZ (Glacier and Permafrost Hazards) framework. Our results show that this lake has increased its areay by 0.1 km2 from 2011 to 2018. Our further investigation highlights that at 100 iterations in MC-LCP model, this lake has the potential of generating a GLOF which can travel 89.1 km downstream and innundate 22.8 km2 of land area, including affecting 205 buildings, 31.8 km of long road and some of the other major infrastructures such as bridges, hydropower plants etc. In this study, we also highlighted the urgent need of extensive monitoring of this highly hazardous lake for mitigating future risk.

World Congress on Disaster Management (WCDM): Mumbai, India: (Jan 29 - Feb 01) [details​]

Title: Modelling the outburst flood from Lhonak Glacial Lake of Sikkim Himalaya for GLOF risk assessment using GIS and HEC-RAS.

Abstract: ‘Himalaya’ is known as the third pole and the water tower of Asia which is the home of many natural hazards. Glacial Lake Outburst Floods (GLOFs) are among the most gigantic natural hazards posing significant threats to the livelihoods and infrastructures downstream. This study assesses the potential downstream risk from the Lhonak glacial lake by modelling the GLOF using GIS based Monte Carlo Least Cost path (MC-LCP) method and compare the model output with more stochastic two dimensional HEC-RAS model. The Lhonak Lake  is located at an elevation of 5218m and is expanding drastically over few decades. High resolution multispectral satellite images of spatial resolution 5.8m (Resourcesat-1, LISS-IV) for two different time periods (2018 and 2011) and the ALOS PALSAR Digital Elevation Model (DEM) data of spatial resolution 12.5m, were processed to derive the required information for modelling. The MC-LCP model was then executed at three different iterations (50, 100 and 500) for simulating the potential GLOF scenarios. The latest glacial lake inventory database of January 2018 revealed that it covered an area of 1.3 km2 which had increased by 0.2 km2 from 2011, probably due to an overall temperature rise across the entire Teesta River Basin, inducing further glacial melt, and held an estimated 51054972 m³ volume of water. At 100 iterations, the lake had the potential to generate a 73.4 km long GLOF event downstream, which would inundate an area of 14 km2 and adversely affect 43 buildings (covering 0.02 km²), 3.2 km length of roads and 1.4 km² and 9 km² of vegetation cover and open land respectively. Whereas, the HEC-RAS flood inundation model showed that a similar GLOF event (73.7 km long) would inundate 23.8 km² of total catchment area and affect 113 buildings (0.01 km²), 14.9 km road lengths, 5.4 km² of vegetation cover and 13.8 km² of open land. Based on the cumulative score of all possible risks of a GLOF event in an outburst scenario using the GIS based MC-LCP model, this lake was considered to be highly hazardous, requiring urgent action to mitigate its high potential risk. It was also noticed that the newly developed MC-LCP method enabled an improved flow routing scenario and was capable of generating acceptable flood extents, even in a region of complex topography, enhancing its status as a significant first-pass hazard assessment tool for flood inundation mapping in the data poor Himalayan region.

National Seminar on Negotiating Nature, Culture and the Future: Presidency University, Kolkata, India: (Feb 28 - Mar 01) [details ]

Title: First-Pass GIS-based MC-LCP method for GLOF modelling in the data-poor Himalayan region.

Abstract: Glacial Lake Outburst Floods (GLOFs) are one of the most potent natural hazards in the Himalayan region, posing significant threat to the millions residing downstream from their occurrence sites along the region’s foothills and extensively threatening built infrastructure and livelihoods. This paper examines the efficacy of a GIS-based Monte Carlo Least Cost Path (MC-LCP) method for assessing the GLOF induced risks from the Phunri Lake, which is located in the source region of the Teesta River, an important right bank tributary of the River Brahmaputra located at in the eastern Indian state of Sikkim. We analysed high resolution multispectral satellite imageries from 2000 to 2018 and digital elevation model for lake inventories,and modelled potential GLOF risk downstream of this lake using GAPHAZ (Glacier and Permafrost Hazards) framework. Our results show that this lake has increased its areay by 0.1 km2 from 2011 to 2018. Our further investigation highlights that at 100 iterations in MC-LCP model, this lake has the potential of generating a GLOF which can travel 89.1 km downstream and innundate 22.8 km2 of land area, including affecting 205 buildings, 31.8 km of long road and some of the other major infrastructures such as bridges, hydropower plants etc. In this study, we also highlighted the urgent need of extensive monitoring of this highly hazardous lake for mitigating future risk.

Royal Geographical Society's Annual International Conference (RGS-IBG): Cardiff University, United Kingdom: (Aug 28-31) [details​]

2018

Title: Dynamics of Land Use Change in the Middle Teesta Watershed (India) between Pre-Monsoon and Post-Monsoon Study Periods, Using Remote Sensing and GIS Technique.

Abstract: Teesta Watershed in the Eastern Himalayan region is predominant by monsoon rainfall on which most of the agricultural activities depend. The aim of this paper is to analyse the changes in Land Use between Pre and Post Monsoon period of a year in the Middle Teesta Watershed of India. Landsat 8 OLI and Cartosat 1 DEM data have been used in both the Erdas Imagine and ArcGIS environments to prepare the Land Use / Land Cover map using supervised classification with maximum likelihood (MXL) method. Based on the land use map of Pre Monsoon (March 2016) and Post-Monsoon (December 2016), a change map has been generated to understand the pattern of land use transformation in terms of changed and unchanged area. Normalised Difference Vegetation Index (NDVI) and Normalised Difference Water Index (NDWI) were used to assess the vegetation cover and distinguish the water body from non-water surface respectively.  The study area covers 168293.79 hectares (1682.94 sq. km) of land from two districts (Darjeeling and Jalpaiguri) of West Bengal State which received 720. 36 cm annual rainfall in 2016. The result shows that the vegetation covered 54.16% of the total area during pre-monsoon period which reduced by 0.76% in post-monsoon and the area of agricultural land decreased by 1.01% during the time because of a massive flood on August 2016 in the study area, whereas, built-up area increased by 1.61% because of new roads, canals and buildings constructed for flood damage control. The change map illustrates that 1713.06 hectares (17.13 sq. km) of agricultural land have been transformed to other land use classes during the study period. An accuracy assessment has also been performed using Kappa Coefficient which shows the coefficient value 1 for pre monsoon land use and 0.99 for post-monsoon land use land cover of the Middle Teesta watershed.

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