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Title: Evaluation of climate and hydrological models for impact projections in the Upper Indus basin
Authors: Pritchard, David Michael William
Issue Date: 2019
Publisher: Newcastle University
Abstract: Water resources in the Indus basin are under acute and growing stress. How climate change will affect this situation in the coming decades depends substantially on responses in the datasparse mountains of the upper basin. However, model projections of changes in the cryosphere-dominated hydrology here are highly uncertain. Integral to this uncertainty are challenges in: characterising near-surface climate fields needed for model input; selecting appropriate model structures to balance process fidelity with data availability; and understanding the wide spread in climate model projections used in impact assessments. As such, this thesis aims to identify pathways for refined hydrological projections in the upper Indus basin through in-depth evaluation of climate, cryospheric and hydrological models. Firstly, using the High Asia Refined Analysis (HAR), the study assesses how relatively high resolution regional climate modelling can help describe spatiotemporal variability in nearsurface climate. The HAR exhibits substantial skill in many respects, but particularly in capturing the complex patterns of precipitation in the basin. Some seasonally varying biases in temperature and incoming radiation suggest deficiencies in snow and cloud representations that are likely resolvable. Secondly, the Factorial Snowpack Model (FSM) is driven with the HAR to examine the feasibility and required structure of process-based snowpack modelling. Model correspondence with local observations and remote sensing is good for a subset of FSM configurations using a prognostic albedo parameterisation, as well as a representation of liquid water retention, drainage and melt/refreezing cycles in the snowpack. The multiphysics approach additionally highlights the inputs and processes needing further investigation, which include the atmospheric stability adjustment. Thirdly, using an adapted FSM program and TOPKAPI-ETH, simplified representations of cryospheric processes are compared with more process-based approaches. This helps to identify where systematic differences in hydrological response occur and their connection with spatial and temporal scales. It is found that an enhanced temperature index (ETI) model exhibits behaviour and climate sensitivity more akin to energy balance formulations than a classical temperature index model. However, there may be structural limits to the fidelity of the ETI formulation under cloudy conditions, while further attention is needed on the translation of surface melt to runoff, especially at high elevations. ii The study then moves to examine controls on regional trends and variability simulated by climate models, focusing on temperature in CMIP5 GCMs. While the models partly reproduce key regional atmospheric circulation influences, variation in summer temperature responses depends on differing snow and albedo representations. Ultimately this may offer some potential to constrain temperature projections. Finally, using CMIP5 and HAPPI GCM outputs, the study explores climate and hydrological projections under selected global warming stabilisation scenarios. This shows that shifts in the timing of runoff are discernible even for low warming targets. Overall water availability may depend particularly on natural variability in precipitation, but in dry years the pressures on water resources in the basin could worsen in future. Further efforts to constrain the range of projections using observations and process-based reasoning are required, but effective water resources management in the basin is likely to depend on increasing resilience to a wide range of climatic and hydrological variability.
Description: Ph. D. Thesis
Appears in Collections:School of Engineering

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