Climate Change in Mountainous River Basins

Climate change in mountainous river basins Understanding climate change impacts and challenges across different spatial scales Klimaatverandering in bergachtige stroomgebieden De effecten en uitdagingen van klimaatverandering op verschillende ruimtelijke schalen (met een samenvatting in het Nederlands) PROEFSCHRIFT ter verkrijging van de graad van doctor aan de Universiteit Utrecht op gezag van de rector magnificus, prof. dr. H.R.B.M. Kummeling, ingevolge het besluit van het college voor promoties in het openbaar te verdedigen op woensdag 11 september 2019 des middags te 12.45 uur door René Reijer Wijngaard geboren op 6 maart 1990 te Heemskerk Promotoren: Prof. dr. W.W. Immerzeel Prof. dr. ir. M.F.P. Bierkens Copromotor: Dr. A.F. Lutz Utrecht Studies in Earth Sciences 193 Climate change in mountainous river basins Understanding climate change impacts and challenges across different spatial scales René R. Wijngaard Utrecht 2019 Promotoren: Prof. dr. W.W. Immerzeel Prof. dr. ir. M.F.P. Bierkens Copromotor: Dr. A.F. Lutz Examination committee: Prof. dr. Yao Tandong Institute of Tibetan Plateau Research, Chinese Academy of Sciences, China Prof. dr. M. Stoffel University of Geneva, Switzerland Prof. dr. ir. E.J. Moors IHE Delft Institute for Water Education, the Netherlands Prof. dr. R.S.W. van de Wal Utrecht University, the Netherlands Prof. dr. Y. Wada International Institute for Applied Systems Analysis, Austria ISBN 978-90-6266-551-8 Published by Faculty of Geosciences of Utrecht University, the Netherlands in: Utrecht Studies in Earth Sciences (ISSN 2211-4335) Printed by ProefschriftMaken || proefschriftmaken.nl Correspondence to René Wijngaard, [email protected]. Cover photo: the Schlatenkees and -bach in Hohe Tauern National Park, Austria (R.R. Wijngaard). Copyright © 2019 René R. Wijngaard This work is licensed under Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (https://creativecommons.org/licenses/by-nc-nd/4.0/). Chapters 2 to 5 and Appendices are based on final author versions of previously published articles, © by René R. Wijngaard and co-authors. More information and citation suggestions are provided at the beginning of these chapters. The mountains are silent - over a loud world The mountains rest - over a bustling world The mountains demand - in a softened world The mountains warm - in a cold world The mountains shine - over a dark world - Reinhold Stecher Contents Summary 11 Samenvatting 15 1 Introduction 19 1.1 Background: climate change in mountainous river basins. 19 1.2 Understanding and modelling climate change impacts at different spatial scales. 21 1.2.1 Understanding and modelling glaciological impacts of climate change at the catchment scale . 23 1.2.2 Understanding and modelling hydrological impacts of climate change at the catchment scale . 28 1.2.3 Understanding and modelling regional/basin-scale climate change impacts . 30 1.3 Research aim and outline. 32 2 Modelling the response of glaciers to historical climate change 35 2.1 Introduction . 35 2.2 Study area. 38 2.3 Data and methods. 39 2.3.1 Historical & reference daily climate forcing. 39 2.3.2 Glacier mass balance and flow model . 42 2.3.3 Model initialization. 44 2.3.4 Model calibration and validation. 45 2.3.5 Sensitivity analysis . 46 2.4 Results. 46 2.4.1 Model calibration and validation. 46 2.4.2 Model sensitivity . 50 2.4.3 Past climate forcing. 50 2.4.4 Glacier evolution & dynamics. 51 2.4.5 Anthropogenic vs. natural influences. 57 2.5 Discussion . 60 2.5.1 Uncertainties and limitations . 60 2.5.2 Shallow ice approximation. 64 2.6 Conclusions and outlook . 64 << Ama Dablam (6814 m) seen from the mountain village Pangboche (4252 m) in Sagarmatha National Park, Nepal (R.R.Wijngaard). 7 3 Hydrological response of glacierized catchments to future climate change 67 3.1 Introduction . 67 3.2 Study area. 69 3.3 Data and methods. 69 3.3.1 Field data . 69 3.3.2 Hydrological modelling . 71 3.3.3 Future climate forcing . 72 3.3.4 Modelling change in glacier extent. 73 3.4 Results. 75 3.4.1 Calibration and validation. 75 3.4.2 Change in future runoff . 76 3.4.3 Seasonality of annual flood peaks. 79 3.4.4 Low flow. 79 3.5 Discussion . 82 3.6 Conclusions and outlook . 84 4 The impacts of climate change on hydrological extremes in upstream mountainous domains 87 4.1 Introduction . 87 4.2 Study area. 90 4.3 Data and methods. 91 4.3.1 Cryospheric-hydrological modelling. 91 4.3.2 Datasets . 93 4.3.3 Calibration and validation. 95 4.3.4 Future climate forcing . 96 4.3.5 Analysis of climatic and hydrological extremes. 97 4.4 Results and discussion. 98 4.4.1 Calibration and validation. 98 4.4.2 Future climate change . .100 4.4.3 Future changes in hydrological extremes . .103 4.4.4 Uncertainties and limitations . 107 4.5 Conclusions. 109 5 Climate change vs. socio-economic development: Understanding the drivers of the future water gap in mountainous river basins 111 5.1 Introduction . .112 5.2 Study area. 115 5.3 Data and methods. 117 5.3.1 Definitions. 117 5.3.2 Modelling framework . .117 5.3.3 Data . .119 5.3.4 Future climate and socio-economic development. 120 5.3.5 Analysis of environmental flows . .121 5.4 Results and discussion. 122 5.4.1 Future climate change . .122 5.4.2 Blue water availability . .122 8 5.4.3 Blue water consumption. 125 5.4.4 Blue water gap. 128 5.4.5 Environmental flows. 132 5.4.6 Comparison with other studies. 134 5.4.7 Uncertainties and limitations . 135 5.5 Conclusions. 137 6 Synthesis 139 6.1 Simulating the response of glaciers under a changing climate . .139 6.2 Hydrological projections at the catchment scale . 140 6.3 Modelling hydrological extremes in mountainous river domains . .141 6.4 Quantifying supply and demand changes in glacier and snowmelt dominated river basins . 143 6.5 Cryospheric-hydrological impacts of climate change in mountainous river basins . .144 6.6 Research novelties . 145 6.7 Challenges, recommendations, and research outlook . 146 6.7.1 Improvements in modelling the essential components of the high-altitude water cycle . .146 6.7.2 Assessing climate change impacts in mountain regions. 152 6.7.3 Bridging the scale gap: from catchment-scale to regional/basin-scale. 154 6.7.4 From understanding climate change impacts to adaptation. 156 Bibliography 159 Appendix A - Supplement to Chapter 3 184 Acknowledgements 186 About the Author 189 Financial support 191 9 10 Summary Freshwater resources are essential for human life. Significant portions of freshwater are provided by mountains, which are largely determined by meltwater originating from glaciers and snow reserves, and orography-induced precipitation that is generally higher in mountain ranges than in surrounding lowlands. Mountain ranges can, due to their large storage potential, act as water towers, sustain seasonal water availability, and provide important water resources for agriculture, drinking water supply, energy production, shipping, tourism, industry, and ecosystems. For this reason, mountain water resources can be considered as important freshwater resources for billions of people living in mountain regions and surrounding lowlands, and it does illustrate the high vulnerability of mountain regions to climate change. Climate change is expected to impact the hydrology and cryosphere of mountainous river basins. Surface and groundwater availability will likely be affected and the frequency and intensity of natural hazards are expected to change. It can therefore be expected that climate change will have a large impact on the society and the environment; impacts that will be amplified with the anticipated socio-economic developments and associated changes in water demand. Understanding climate change impacts in mountainous river basins is challenging due to the complexity of the mountain environment and the wide range of scales on which mountain-hydrological processes can occur. This makes it necessary to examine these effects at different spatial scales. The research described in this thesis aims therefore at understanding the cryospheric and hydrological impacts and challenges of climate change across different spatial scales in mountainous river basins. To this end, novel modelling approaches have been developed and applied to assess the effects of climate change at catchment- and regional/basin- scale. Ongoing global warming has resulted in a widespread retreat of glaciers since the end of the Little Ice Age. To attribute the response of glaciers to natural and anthropogenic historical climate change over time a spatially-distributed coupled glacier mass balance and ice-flow model is developed and applied that does not require a priori information about the flowline geometry of glaciers. The model is applied for the debris-covered Langtang Glacier in the Central Himalayas and the clean-ice Hintereisferner in the European Alps from the end of the Little Ice Age (1850) to the present-day (2016). The model is forced with four bias-corrected climate models that represent region-specific cold-dry, cold-wet, warm-dry, and warm-wet climate conditions. To isolate the effects of human- induced climate change on glacier mass balance and dynamics, runs are selected from the climate models with and without further anthropogenic forcing after 1970 until 2016. The model outcomes reveal that both glaciers experience the largest reduction in area and volume under warm climate conditions and that simultaneously with changes in glacier area and volume, surface velocities generally decrease over time. Without further anthropogenic forcing the analysis reveals that the decline in glacier area and volume is smaller, indicating that the response of the two glaciers can mainly be attributed to anthropogenic climate change. Here, a debris-covered glacier shows a limited retreat and tends to lose less mass due to insulation of the glacier surface by a layer of supraglacial debris, where a clean-ice glacier responds faster to climate change and shows a larger retreat.

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