Impacts of Climate Change on Water Resources of Nepal The Physical and Socioeconomic Dimensions Dissertation Zur Erlangung des Grades: Doktor der Wirtschaftswissenschaften (Dr. rer. Pol.) an der Universität Flensburg von Narayan Prasad Chaulagain, M. Sc. Nepal Flensburg, 2006 Gutachter : 1. Prof. Dr. Olav Hohmeyer (Betreuer) Universität Flensburg Internationales Institut für Management Energie- und Umweltmanagement 2. Prof. Dr. Stephan Panther Universität Flensburg Internationales Institut für Management 3. PD Dr. Sc. Alfred Becker Potsdam Institute for Climate Impact Research ii Contents List of tables vi List of figures vii Acronyms and abbreviations ix Acknowledgement xi Abstract xii 1 Problem statement and objectives of the study 1 1.1 Background of the study and problem statement 1 1.2 Objectives 5 1.3 Organisation of the report 6 2 State-of-the-art review and development of hypotheses 7 2.0 General 7 2.1 Global climate change 7 2.1.1 Global temperature change 8 2.1.2 Change in precipitation and atmospheric moisture 10 2.2 Climate change in the Himalayan region and Nepal 11 2.2.1 Climate change in the Himalayas 11 2.2.2 Climate Change in Nepal 13 2.2.2.1 Change in temperature 14 2.2.2.2 Change in precipitation 14 2.3 Physical impacts of climate change 15 2.3.1 Impacts on water resources and hydrology- a global perspective 15 2.3.2 Impacts of climate change on water resources – the Himalayan perspective 17 2.3.2.1 Snow and glacier 17 2.3.2.2 River discharge 19 2.4 The socioeconomic impacts 20 2.4.1 Effects on the water withdrawals 21 2.4.2 Agriculture and food security 21 2.4.3 Effects on the hydropower potential 23 2.4.4 Effects on extreme events 24 2.4.4.1 Changes in flood and drought frequency 24 iii 2.4.4.2 Glacier lake outburst floods 25 2.5 Projected future climate 27 2.5.1 Future global climate 27 2.5.2 Climate change scenarios for Nepal 27 2.6 Open questions 28 2.7 Development of hypotheses 29 3 Research methodology 30 3.1 Study design and context 30 3.2 Source of data 30 3.3 Detecting the climate change 31 3.3.1 Testing for significance 32 3.4 Estimating the physical impacts of climate change 34 3.4.1 Impacts of climate change on river runoff: the Water Balance Model - WatBal 34 3.4.2 Impacts on glacier mass balance in the Nepal Himalayas 36 3.4.2.1 Empirical glacier mass balance model 37 3.4.2.2 Application of the empirical glacier mass balance model 38 3.4.2.3 Sensitivity of the glaciers in the Nepal Himalayas to temperature rise 39 3.5 Estimating the socioeconomic impacts of climate change 40 3.5.1 Impacts on the total water availability in Nepal 41 3.5.2 Impacts on the hydropower potential 41 3.5.3 Impacts on the water balance situation 42 3.5.3.1 The FAO Penman-Monteith method 43 3.5.4 Climate change impacts on agricultural production, poverty and food security 44 3.5.5 Impacts on extreme weather events 44 3.6 Limitations of the study 45 4 Empirical findings on climate change in Nepal 46 4.0 General 46 4.1 Temperature change 46 4.1.1 Empirical findings on temperature change 46 4.1.2 Discussion of empirical findings on temperature change 48 4.2 Precipitation change 51 4.2.1 Empirical findings on change in precipitation amount 51 iv 4.2.2 Empirical findings on change in number of rainy days 52 4.2.3 Discussion of empirical findings on precipitation change 54 4.3 Conclusion 55 4.3.1 Summary of findings 55 4.3.2 Open questions 56 5 Empirical findings on the physical impacts 57 5.0 General 57 5.1 Impacts on evapotranspiration and moisture balance 57 5.1.1 Empirical evidence on impacts on evapotranspiration and moisture balance 57 5.1.2 Discussion about the impacts on evapotranspiration and moisture balance 60 5.2 Impacts on the river flows 60 5.2.1 Runoff modelling of the Bagmati River at Chovar 62 5.2.2 Runoff modelling of the Langtang Khola at Langtang 64 5.2.3 Synthesis of the runoff modelling of the Bagmati River and the Langtang Khola 65 5.2.4 Discussion of the empirical evidence on the impacts on the river flows 69 5.3 Impacts of a temperature rise on snow and glacier systems 70 5.3.1 General findings 70 5.3.2 Sensitivity analysis of glacier mass balance to temperature rise 72 5.3.3 Discussion about the impacts of climate change on snow and glaciers 80 5.4 Conclusion 83 5.4.1 Summary of findings 83 5.4.2 Open questions 84 6 Empirical findings on the socio-economic impacts of climate change 85 6.0 General 85 6.1 Impacts on the water balance, agriculture and food security 85 6.1.1 Impacts on the irrigation water requirement 85 6.1.2 Impacts on the water balance situation 87 6.1.3 Impacts on the agricultural production, food security and poverty 90 6.1.4 Discussion of the impacts of climate change on water balance, Agriculture and food security 97 6.2 Impacts on the hydropower potential 99 6.2.1 Empirical findings of the impacts on the hydropower potential 99 v 6.2.2 Discussion of impacts on the hydropower potential 103 6.3 Impacts on the extreme events 104 6.3.1 Impacts on the glacier lake outburst floods 104 6.3.2 Impacts on droughts, floods and landslides 108 6.3.2.1 Snow-covered area and the extreme floods 108 6.3.2.3 Droughts, floods and landslides caused by the changing precipitation pattern 111 6.3.3 Discussion of the impacts of climate change on the extreme events 114 6.4 Conclusion 116 6.4.1 Summary of the findings 116 6.4.2 Open questions 116 7 Conclusions and recommendations 118 7.0 General 118 7.1 Conclusions 118 7.2 Recommendations 119 7.3 Propositions for future research 121 Bibliography 123 Annex vi List of Tables Table 2.1 GCM estimates of temperature and precipitation changes for Nepal 28 Table 3.1 Descriptions of reference meteorological stations 31 Table 4.1 Annual and seasonal mean temperature trends of reference stations 47 Table 4.2 Minimum, maximum and mean annual temperature trends 48 Table 4.3 Annual temperature trends of reference stations for 1988-2000 48 Table 4.4 Analysis of trends in annual precipitation records 51 Table 4.5 Fluctuations of number of rainy days at reference stations 52 Table 4.6 Trends in number of rainy days as per daily precipitation 53 Table 4.7 Analysis of precipitation at Rampur, Kathmandu and Daman 54 Table 5.1 Sensitivity analysis of atmospheric moisture to a temperature rise 58 Table 5.2 Sensitivity of soil moisture storage with a temperature rise at Kathmandu Airport 59 Table 5.3 Precipitation and runoff of the Langtang Khola and the Bagmati River 61 Table 5.4 Sensitivity of the river runoff to climate change at the Chovar station 63 Table 5.5 Sensitivity of the Langtang Khola runoff to climate change 65 Table 5.6 Sensitivity of monthly runoff to temperature and precipitation changes 67 Table 5.7 Summary of sensitivity analysis of glaciers at Langtang 74 Table 5.8 Glacier mass balance rates with different temperature change scenarios 76 Table 5.9 Sensitivity of glacier ice-reserve to a temperature rise in Nepal 77 Table 6.1 Sensitivity of potential evapotranspiration to a temperature rise 86 Table 6.2 Sensitivity of the irrigation water requirement to a warming 87 Table 6.3 Water supply and demand situation at Chovar 89 Table 6.4 Poverty analysis and measurement in Nepal 91 Table 6.5 Sensitivity of calorie supply to a warming for average population 95 Table 6.6 Sensitivity of calorie supply to a warming for different income groups 96 Table 6.7 All-Nepal average monthly and annual hydrograph 100 Table 6.8 Sensitivity of hydropower potential in Nepal with temperature rise 101 vii Table 6.9 Sensitivity of hydroenergy potential in Nepal with temperature rise 102 Table 6.10 Sensitivity of melt- and rainwater to temperature change in Nepal 105 Table 6.11 Snow-covered areas and the ratio of maximum to minimum instantaneous flows in some selected hydrological stations 108 Table 6.12 Sensitivity of snowfall to temperature increases in the Nepal Himalayas 112 Table 6.13 Sensitivity of rainfall to temperature increases in the Nepal Himalayas 113 List of Figures Figure 2.1 Variations of the earth’s surface temperature 9 Figure 2.2 Annual temperature trends for 1976-2000 9 Figure 2.3 Annual precipitation trends for 1900-2000 10 Figure 2.4 Temperature trend as a function of elevation on the Tibetan Plateau 12 Figure 3.1 Conceptualization of water balance for the WatBal model 35 Figure 4.1 Mean temperature anomalies (1971-2000) 46 Figure 4.2 Fluctuation of standardised precipitation (1971-2000) 52 Figure 5.1 Mean monthly moisture balance at Kathmandu Airport 58 Figure 5.2 Comparative mean monthly hydrographs 61 Figure 5.3a Modelling the Bagmati River Runoff at Chovar (1976-1980) 63 Figure 5.3b Modelling the Langtang Runoff at Langtang (1993-1998) 64 Figure 5.4 Sensitivity of the runoff to temperature at Chovar 66 Figure 5.5 Sensitivity of runoff to precipitation at Chovar 67 Figure 5.6 Comparative sensitivity of river runoff (T+2, P-10 scenario) 68 Figure 5.7 Basin areas at Langtang 70 Figure 5.8 Average glacier mass balance with altitudes 71 Figure 5.9 Monthly glacier mass balances at Langtang 72 Figure 5.10 Sensitivity of glacier mass balance in altitudes 73 Figure 5.11 Sensitivity of glacier-ice reserve to a warming 76 Figure 5.12 Sensitivity of glacier surface area to a warming 78 viii Figure 5.13 Distribution of glaciers with areas in Nepal 78 Figure 5.14 Sensitivity of glaciers to a warming in Nepal 79 Figure 5.15 Sensitivity of glacier-melt water to a warming 79 Figure 5.16 Sensitivity of total water availability to a warming in Nepal 80 Figure 6.1 Water balance at Chovar 88 Figure 6.2 Sensitivity of annual water balance situation at Chovar 89 Figure 6.3 Change in water balance at Chovar 90 Figure 6.4 Consumption patterns in Nepal 92 Figure 6.5 Sensitivity of hydropower potential to warming 101 Figure 6.6 Sensitivity of liquid water to a warming 105 Figure 6.7 Tsho Rolpa Glacier Lake and its development 107 Figure 6.8 Snow-covered area and extreme floods in Nepal 109 Figure 6.9 Hypothetical changes in peak discharges of the Bagmati River at Chovar 110 ix Acronyms and Abbreviations AD of the Christian era (from the Latin anno domini) AET actual evapotranspiration BP before present CBS Central Bureau of Statistics, Nepal CO2 carbon dioxide DHMN Department of Hydrology and Meteorology, Nepal DIO Department of Irrigation, Nepal e.g.