Browsing by Subject "Himalaya"
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Item Debris-covered glaciers : modeling ablation and flood hazards in the Nepal Himalaya(2016-05) Rounce, David Robert; McKinney, Daene C.; Maidment, David R; Hodges, Ben R; Catania, Ginny A; Yang, Zong-LiangDebris-covered are ubiquitous in the Nepal Himalaya and significantly alter the glaciers response to climate change and have large implications on the development of glacial lakes. The thickness of the debris is largely heterogeneous over the course of the glacier thereby promoting ablation in areas of thin debris and retarding ablation in areas of thick debris. The debris thickness typically increases towards the snout of the glacier, but can be difficult to measure as field measurements are time-consuming and laborious. This body of work utilizes satellite imagery in conjunction with a debris-covered glacier energy balance model to reasonably estimate the spatial variations in debris thickness for glaciers in the Everest region of Nepal. Sub-debris ablation rates may be computed using the same energy balance model, but requires detailed information regarding the properties of the debris and the surface processes. Detailed field data was collected over the 2014 melt season on Imja-Lhotse Shar Glacier to estimate many of the debris properties. This data was also used to model the sub-debris ablation rates to develop an understanding of the critical properties (i.e., thermal conductivity, albedo, and surface roughness) and processes (i.e., accounting for the latent heat flux) required to accurately model the impact of the debris. The heterogeneous debris cover often causes higher melt rates upglacier, which diminishes the glacier’s topographic gradient thereby promoting glacier stagnation and the development of glacial lakes. These glacial lakes form behind terminal moraines comprising soil and loose boulders that are susceptible to fail causing a glacial lake outburst flood (GLOF). GLOFs can have devastating impacts on infrastructure and communities located downstream; however, assessing the risks associated with these floods has traditionally required detailed field campaigns that are difficult to perform as these glacial lakes are located in remote areas at high altitudes. This body of work develops a holistic hazard assessment using solely remotely sensed data to objectively characterize the threat of a GLOF. This hazard assessment provides valuable information concerning potential GLOF triggers that may be used to direct future field campaigns and ultimately the management actions associated with these glacial lakes.Item Global change : projecting expansion of invasive species and climate change impacts at the tree-tundra ecotone in the Himalaya(2014-08) Mainali, Kumar Prasad; Parmesan, Camille, 1961-; Singer, Micheal; White, Joseph; Young, Kenneth; Simpson, BerylModeling the distribution of species, especially of invasive species in non-native ranges, has multiple challenges. We develop some novel approaches to species distribution modeling aimed at reducing the influences of these challenges and improve realism of projections. We estimated species-environment relationship with four modeling methods, viz., random forest (RF), boosted regression trees (BRT), generalized linear models (GLM), and generalized additive models (GAM), running each of them with multiple scenarios of (1) sources of occurrences and geographically isolated background ranges, (2) approaches of drawing background points, (3) alternate sets of predictor variables. When a species' distribution is in a non-equilibrium state, as is the case for most invasive species, model projections are very sensitive to the choice of training dataset. Contrary to previous studies, we found that model accuracy is much improved by using a global dataset for model training (both presences and background points from the world), rather than restricting data input to the species' native range. Projections outside the training region, especially in invaded regions, can be very different depending on the modeling method used. Globally projecting, we show that vast stretches of currently uninvaded geographic spaces in multiple continents harbor highly suitable habitats for Parthenium. Projections away from the sampled space (i.e. into areas of potential future invasion), can be very different with different modeling methods, raising questions about the reliability of ensemble projection. Data-driven models that efficiently fit the dominant pattern but exclude highly local features in dataset and model interactions as they appear in data (e.g., boosted regression trees) improve generalization of the species distribution modeling. Alpine treelines are responding to current climate change worldwide. To understand tree line dynamics and its potential drivers, we studied the primary two dominant tree species, Abies spectabilis (AS) and Rhododendron campanulatum (RC), on the north facing slope of two mountains in central Nepal. We determined spatial pattern of regeneration potential, mortality and abundance for various size/age classes, and we identified the most important drivers of such patterns. We also conducted a reciprocal transplant experiment on saplings of RC, moving them between species limit and treeline that were spaced apart by 150m. Young plants (<2m tall) of RC have higher density above treeline than below treeline. Mature plants (>2m tall) of RC, on the contrary, show insignificant trend towards higher density below treeline than above. Mortality of RC was always lower above treeline than below, independent of size class. AS saplings have extremely lower density above treeline than below, with mature plants being virtually absent above treeline. Elevation was identified as the only significant predictor of the decrease in density of both species above treeline. The saplings are progressively younger and shorter with distance above treeline. Both species are regenerating faster above treeline than below. These results are consistent with upward shift of the tree line of RC as a result of recent amelioration of temperature. Climatic extremes during spring affect mortality and leaf size whereas growth is affected by summer climate. Individuals from the species limit, if they survive, perform better when moved downhill than they do at home, and also out-perform the locals. Although the upper elevational boundary of RC is shifting upward, these results indicate that strong differences still exist between individuals across a short elevational gradient, with individuals at the extreme limit of the species range being more tolerant to extreme climate conditions but less tolerant of competition compared to individuals only 150m lower in elevation.