IMPACT OF CLIMATE VARIABILITY ON GLACIER MASS BALANCE IN REGIONAL, BASINAL AND LOCAL SCALE

Abstract

Glacier Mass Balance (MB) is essential in order to understand the response of glaciers with changing climate system. The warming climate may lead to a shift in the hydrological regime of the glacier in terms of snow-fed runoff timing and snow-fed to rainfall-dominated hydrological regimes. Apart, the changing glacier mass can modify the hydrological cycle and river flow, which also creates concerns about the sustainability of streamflow in the summer season. Therefore, reliable estimation of MB and its interaction with climate are important to quantify the response of glacier change with future climatic variability. The mountains of the Himalayan region hold the largest ice masses outside the polar regions, even several major rivers originated from these mountains, and its downstream regions are densely populated. However, the Himalayan mountains are characterized by data scarcity due to their complex topography and varying climatic conditions, limiting the continuous monitoring of glacier changes using in-situ observation. In a changing climatic boundary condition, an appropriate model for MB estimation and glacier characterization are required that can represent the key controlling mechanism. Due to the lack of continuous glaciological and meteorological observations, the monitoring and modelling of the MB over the Himalayan glaciers are a major challenge. To overcome this limitation, the utility of remote sensing data presented a great advantage for MB estimation in time and space. In this thesis, we use Gravimetric twin satellite data for regional surface mass change measurement over the glaciers of the Karakoram and Himalayan (KH) region. The spatio-temporal mass change distribution and its trends are estimated in order to assess the hotspot/coldspot region of mass variation and their further influence on streamflow in the near future. The regional mass change estimation is important because it provides us insight into what is exactly happening in the KH region other than glacier mass loss. During the study of regional-scale mass variation, we have also established an interconnection between the mass change and climatic (former) variables as well as with the other influential (impacted/latter) variables. After analyzing the regional mass change and influence of forcing variables, we selected the Chandra basin (western Himalayas) for the basinal scale glacier MB estimation. This basin is mainly considered due to the higher mass loss (observed from the regional-based mass variation); therefore, a detailed investigation is needed. A spatially distributed mass balance model has been developed for the basinal scale to ensure that all the necessary physical variables and processes are correctly incorporated into the model. A new multi-step physical-based Energy Balance Model (EBM) has been carried out by parameterizing the energy balance components and also modelled the air temperature at the spatial extent. To test the model, a calibration/validation has been performed using the in-situ observation of the Himansh station (located within the basin) and with the published MB. The model observations suggested that the spatially distributed EBM at the catchment scale can bridge the gap between regional observation-based mass change and point-scale-based studies. The results of basinal MB demonstrated that the Batal glacier shows a significant loss in its mass than the nearby glaciers, i.e., Sutri Dhaka glacier (showing a considerable mass loss) over the observational period. These two glaciers have similar climatic conditions and orientations, despite having varying melt conditions by controlling debris thickness over the glacier surface. Therefore, we have selected the Batal and Sutri Dhaka glaciers for locale-scale glacier MB estimation. Over these two selected glaciers, the glacier feature classification and shift in isotherm have been quantified to monitor temporal glacier variation. Then, the glacier surface velocity, modelled ice thickness, and total stored volume are estimated against the remote sensing data. The associated uncertainties of the modelled ice thickness and surface velocity are measured to test the reliability of the observations. Despite this, the locale scale MB has been calculated by the difference between different Digital Elevation Models (DEMs) and compared the results with the reported MB. The model finding of locale MB illustrated that the Batal glacier experienced more mass loss due to the presence of debris that contributes to a higher rate of melting than the Sutri Dhaka glacier. To derive the MB from regional to local, we have used a hierarchical methodology to connect the changes of MB with the spatial extent and also with the climatic interaction. With this methodology, we have not required in-situ observations for modelling the MB; however, it uses field observation for calibration and validation of the obtained results. The overall varying climatic variables and their relationship with water availability are presented in objective-1. The regional scale mass changes and contribution of hydro-meteorological variables are discussed in objective-2, and the model developed in objective-3. Finally, a detailed mass balance analysis and glacier characterization are mentioned in objective-4. Overall, the obtained results and developed model are likely to be important for the research community of glaciologists, hydrologists, decision-makers, water resource managers, and civil engineers (for understanding the streamflow under the summer season at the time of dam construction). This thesis can also be a benchmark for modellers in the high-altitude region and facing the problem of data scarcity to evaluate their experimental approaches. In a broader context, the results of this thesis can be used for predicting the river runoff and water stress/water availability in both upstream and downstream regions.