Water Global Practice Discussion Paper Water, Poverty, and the Economy Physical Impacts of Climate Change on Water Resources Fernando Miralles-Wilhelm, Leon Clarke, Mohamad Hejazi, Sonny Kim, Kelly Gustafson, Raul Muñoz-Castillo, and Neal Graham About the Water Global Practice Launched in 2014, the Word Bank Group's Water Global Practice brings together financing, knowledge, and implementation in one platform. By combining the Bank's global knowledge with country investments, this model generates more firepower for transformational solutions to help countries grow sustainably. Please visit us at www.worldbank.org/water or follow us on Twitter at @WorldBankWater. 3 Introducing Commercial Finance into the Water Sector in Developing Countries Physical Impacts of Climate Change on Water Resources Fernando Miralles-Wilhelm, Leon Clarke, Mohamad Hejazi, Sonny Kim, Kelly Gustafson, Raul Muñoz-Castillo, and Neal Graham © 2017 International Bank for Reconstruction and Development / The World Bank 1818 H Street NW, Washington, DC 20433 Telephone: 202-473-1000; Internet: www.worldbank.org This work is a product of the staff of The World Bank with external contributions. The findings, interpretations, and conclusions expressed in this work do not necessarily reflect the views of The World Bank, its Board of Executive Directors, or the governments they represent. The World Bank does not guarantee the accuracy of the data included in this work. The boundaries, colors, denominations, and other information shown on any map in this work do not imply any judgment on the part of The World Bank concerning the legal status of any territory or the endorsement or acceptance of such boundaries. Rights and Permissions The material in this work is subject to copyright. Because The World Bank encourages dissemination of its knowledge, this work may be reproduced, in whole or in part, for noncommercial purposes as long as full attribution to this work is given. Please cite the work as follows: Miralles-Wilhelm, Fernando, Leon Clarke, Mohamad Hejazi, Sonny Kim, Kelly Gustafson, Raul Muñoz-Castillo, and Neal Graham. 2017. “Physical Impacts of Climate Change on Water Resources.” Discussion Paper. World Bank, Washington, DC. Any queries on rights and licenses, including subsidiary rights, should be addressed to World Bank Publications, The World Bank Group, 1818 H Street NW, Washington, DC 20433, USA; fax: 202-522-2625; e-mail: pubrights@worldbank.org. Cover design: Jean Franz, Franz & Company, Inc. Contents Introduction 1 Research Methods 3 Results and Discussion 8 Projected Volumetric Inflow 12 Projected Water Scarcity 14 The Socioeconomic Impacts of Future Development Scenarios on Water Scarcity 14 Projected Effects of Mitigation Policies 18 Conclusion 22 Notes 23 References 24 Physical Impacts of Climate Change on Water Resources iii Abstract T  his paper documents an initial study focused on understanding the physical impacts of climate change on water resources throughout the world. The research performed in this study is based on the application of an Integrated Assessment Model to quantify these impacts for a wide range of scenarios of socioeconomic devel- opment that offer a mix of possible futures for the availability, use, and management of water resources. Through this research and analysis, this study provides an integrated qualitative and quantitative understanding of the implications of several selected issues, including climate change and mitigation, and socioeconomic and technological develop- ments, on water scarcity and water-energy-food interactions in a global context. The understanding gained through this analysis is expected to contribute to the ongoing dialogue on the sustainability of multiple human activities and their trajectories toward global development pathways. Introduction The precise consequences of climate change on the hydrological cycle are uncertain, which makes adaptation Despite the well-recognized role of water in transmit- especially challenging. Uncertainty regarding impacts is ting climate impacts to some of the growth drivers of partly a consequence of the limitations of climate models. the economy, the water sector has been largely ignored Despite improvements in climate science, the Global in climate change deliberations. The impacts are pro- Circulation Models (GCMs) developed to project climate jected to vary by region, and are likely to include futures generate a wide range of projections that often changes in average hydroclimate patterns (precipita- disagree on both the direction and magnitude of precip- tion, surface runoff, and stream flow), as well as itation changes. Furthermore, GCMs have not been increases in the probability of extreme events. Climate designed to predict  changes in the hydrological cycle shocks are likely to impose higher costs than gradual precision required for planning and manag- and lack the ­ changes in climate averages. Prudent management of ing water resources. These errors are compounded when water resources will be pivotal in addressing the cli- projections are “downscaled” from regional to the finer ­ mate challenge—both for adapting to the effects of cli- spatial scales necessary for planning and the design of mate change and for meeting global goals to mitigate infrastructure. In addition, changes in the hydrological greenhouse gases (GHG). cycle imply that future water systems may not resemble the past (nonstationarity), so historic trends—as used in This discussion paper was authored by Fernando Miralles-Wilhelm, engineering designs—no longer serve as a reliable guide Earth System Science Interdisciplinary Center, University of for assessing and managing future risks. Maryland; Leon Clarke, Joint Global Change Research Institute, Pacific Northwest National Laboratory and University of Maryland; Identifying and analyzing the consequences of climate Mohamad Hejazi, Joint Global Change Research Institute, Pacific Northwest National Laboratory and University of Maryland; Sonny change in water resources requires integrated model- Kim, Joint Global Change Research Institute, Pacific Northwest ing that allows proper incorporation of the potential National Laboratory and University of Maryland; Kelly Gustafson, impacts of climate in the hydrological cycle into all Department of Geographical Sciences, University of Maryland; Raul Muñoz-Castillo, Department of Geographical Sciences, University of major sectors that use water, such as the urban, envi- Maryland; and Neal Graham, Department of Atmospheric and Oceanic ronment, agriculture, and energy sectors. It also Science, University of Maryland. Physical Impacts of Climate Change on Water Resources 1 requires the use of economic resources has advanced greatly in the past decade. This paper aims to investigate tools to determine the eco- IAMs use a set of different assumptions and interre- the impacts of climate change nomic costs and benefits of dif- lated factors simultaneously and include both physi- on water resources throughout ferent adaptation strategies. cal and social science models that consider the world, and specific effects demographic, political, and economic variables that on water-dependent sectors The use of Integrated affect greenhouse gas emission scenarios. IAMs allow of the economy, such as urban, Assessment Models (IAMs) to researchers to explore interactions between sectors energy, and agriculture sectors. identify the physical impacts and to understand the potential ramifications of of climate change on water ­climate actions. Figure 1 illustrates a typical IAM. Figure 1. A Typical Integrated Assessment Model (IAM) Human Earth Systems Managed Economy Security Food ecosystems Population ENERGY Transport Settlements Science Technology Health Atmospheric Coastal Carbon Chemistry Sea Ice Zones Cycle Earth system Oceans Hydrology Ecosystems models Biogeophysical Earth Systems 2 Physical Impacts of Climate Change on Water Resources Research Methods can also be used to compare the relative effects of socioeconomic and technological changes to the The analysis in this paper is conducted utilizing an effects of climate change. IAM called the Global Change Assessment Model (GCAM) as the main analytical tool.1 The analysis Finally, the study examines the implications of limited involves setting up and running multiple GCAM sim- water resources on energy and agricultural decisions. ulation scenarios to shed light on three important Simulations are carried out with and without con- questions: straining water resources as a limited resource in 1. What are the physical impacts of climate change water-using sectors (such as domestic water supply, on  water scarcity around the world, and particu- energy, and agriculture). The results shed light on any larly on surface runoff? changes in water demands by sector due to changes in water availability in the coming decades. 2. What are the impacts of future development scenar- ios under consideration on water scarcity? A ssessment Model Using the Global Change ­ 3. What are the impacts of implementing climate (GCAM) to Quantify Impacts of ­Climate Change change mitigation on water scarcity? The research questions posed in this paper are focused To investigate the physical impacts of climate change on quantifying the impacts of climate change, future on water scarcity, the results from multiple GCMs are development scenarios, and intervention policies on used as inputs into GCAM, to assess the level of uncer- water resources throughout the world. This research tainty propagating from climate models and their impli- also lays the groundwork for an analytical tool that can cations on water scarcity conditions at the scale of be used to support decisions not only in the scenarios individual countries. Three GCMs that span the range of documented in this paper, but other policy and interven- uncertainty (wet, dry, and normal) are selected to drive tion options that may be considered moving forward. the GCAM simulations, with and without accounting for The methodological procedure used in this investi- the impacts of climate change on water availability. The gation can be summarized by the following major results allow for a comparison between the uncertain- steps: ties surrounding climate models and the corresponding distribution of water scarcity around the world. • A given climate model is selected as input, providing spatial and temporal distributions of climate vari- Next, several Shared Socioeconomic Pathway scenar- ables such as temperature and precipitation. ios (SSPs) are simulated, using hydrologic inputs from the GCMs, to show how socioeconomic and techno- • These climate variables are used in GCAM to run its logical development might affect water demands, water supply (hydrology) submodel (Hejazi et al. and consequently water scarcity in different basins. 2013, 2014a, 2014b). SSPs describe potential future pathways for the evo- • The GCAM numerical solution procedure is based on lution of key aspects of society that would affect our a partial-equilibrium economics approach that is abilities to mitigate, and adapt to, climate change. documented in references such as Edmonds and Five SSPs were selected for this study that reflect a Reilly (1983), Brenkert et al. (2003), Kim et al. (2006), broad range of possibilities. The analysis focuses on and Clarke et al. (2007). quantifying regional water demands for different uses of water resources, and projecting river basins • GCAM outputs include water withdrawal under water scarcity. The results of these simulations (demands) for each of the major water-using Physical Impacts of Climate Change on Water Resources 3 economic sectors (such as food production, energy ­ Map 1. GCAM Links Economic, Energy, Land-use, Water, and Climate Systems generation, and municipal supply); these outputs are also used to calculate a water scarcity indicator (WSI). • These outputs are generated for each one of the modeling scenarios simulated in GCAM (including 32 energy the reference scenario, SSPs, mitigation scenario, regions as discussed later in this paper). A Brief Description of GCAM 283 land The Global Change Assessment Model (GCAM) is an regions Integrated Assessment Model (IAM) for exploring consequences and responses to global change.2 Climate change is a global issue that impacts all 233 water regions of the world and all sectors of the global basins economy. Thus, any responses to the threat of cli- mate change, such as policies or international agree- ments to limit greenhouse gas emissions, can have wide-ranging consequences throughout the energy system, as well as on water resources, energy genera- numerous technology options to produce, transform, tion, food production, land use, and land cover. IAMs and provide energy services as well as to produce agri- endeavor to represent all world regions and all sec- culture and forest products, and to d ­ etermine land use tors of the economy in an economic framework in and land cover. Outputs of GCAM include projections order to explore interactions between sectors and of future energy supply and demand and the resulting understand the potential ramifications of climate greenhouse gas emissions; and radiative forcing change mitigation actions. and  climate effects of 16 greenhouse gases, aerosols, and short-lived species at 0.5×0.5 degree resolution—​ A key advantage of GCAM over some other IAMs is that contingent on assumptions about future population, ­ it is a Representative Concentration Pathway (RCP)- economy, technology, and climate mitigation policy. class model. This means it can be used to simulate sce- On the water side, six  major water use sectors are narios, policies, and emission targets from various considered: agricultural irrigation, municipal water ­ sources, including the Intergovernmental Panel on supply, primary resource extraction (energy/mining), Climate Change (IPCC). livestock production, electricity generation, and indus- GCAM is formulated in a dynamic-recursive modeling trial manufacturing. approach, with technology-rich representations of the economy, energy sector, land use, and water resources Representative Concentration Pathways (RCPs) linked to climate models that can be used to explore Representative concentration pathways are used to climate change mitigation policies including carbon ­ make assumptions about climate change mitigation taxes, carbon trading, regulations, and accelerated levels. RCPs are four greenhouse gas concentration deployment of energy technology (map  1). Regional (not  emissions) trajectories adopted by the IPCC for population and labor productivity growth assumptions its fifth Assessment Report (AR5) in 2014 (Moss et al. drive the energy and land-use systems, employing 2008). They describe four possible climate futures, all 4 Physical Impacts of Climate Change on Water Resources of which are considered possible depending on how resources; groundwater data are obtained from the much greenhouse gases are emitted in the years to FAO’s Aquastat database.4 come. The four RCPs—RCP2.6, RCP4.5, RCP6.0, and • Runoff and inflow data are aggregated from monthly RCP8.5—are named after a possible range of radiative to average annual estimates. forcing values in the year 2100 relative to preindustrial • The WSI for each country is calculated (annually) as: values (increases of +2.6, +4.5, +6.0, and +8.5 W/m2, respectively) (Weyant et al. 2009). Demands WSI = Runoff + Inflow The RCPs are consistent with a wide range of possi- ble  changes in future anthropogenic (man-made) A water scarcity index value of 0.4 or higher (WSI ≥ 0.4) GHG  emissions. RCP2.6 assumes that global annual is used in this study to denote severe scarcity; (0.2 ≤ GHG emissions (measured in CO2-equivalents) peak WSI < 0.4) denotes moderate scarcity; (0.1 ≤ WSI < 0.2) between 2010 and 2020, with emissions declining denotes low scarcity; and (WSI<0.1) denotes no scar- substantially thereafter. Emissions in RCP4.5 peak ­ city, or abundant water resource availability in a coun- around 2040, then decline. In RCP6.0, emissions try as compared with water demands. peak around 2080, then decline. In RCP8.5, emis- sions continue to rise throughout the twenty-first Global Climate Models (GCMs) century. For this study, three different Global Climate Models (GCMs) are selected to represent different climate For the purposes of this study, a “no climate policy” model assumption and formulations, in an effort to reference scenario has been implemented in GCAM to provide a robust envelope of impacts of climate change reflect “reference” or baseline efforts toward climate on water resources and the corresponding analysis of mitigation. RCP4.5 is used as a “climate policy” sce- results. nario to reflect the implementation of climate mitiga- tion policies in GCAM simulations. CCSM. The Community Climate System Model5 is a GCM  developed by the University Corporation for Water Scarcity Index Atmospheric Research (UCAR). The coupled compo- The Water Scarcity Index (WSI) for a given GCAM sim- nents include an atmospheric model (Community ulated scenario is determined as follows: Atmosphere Model), a land-surface model (Community Land Model), an ocean model (Parallel Ocean Program), • Water demands (total water withdrawals) are simu- and a sea ice model (Community Sea Ice Model) lated in GCAM; these results are downscaled to the (Hoffman 2006). grid scale and mapped up to country scale. • The hydrology (water supply) module in GCAM is GISS. The Goddard Institute for Space Studies6 GCM is used to generate runoff estimates using climate primarily aimed at the development of coupled atmo- sphere-ocean models for simulating Earth’s climate information from the three GCMs—CCSM, GISS, and system. Primary emphasis is placed on investigation of FIO-ESM—at the basin level.3 climate sensitivity globally and regionally, including • The surface runoff generated is mapped up to the the climate system’s response to diverse forcings such country scale. as solar variability, volcanoes, anthropogenic and nat- • The total inflow into each country is calculated as ural emissions of greenhouse gases and aerosols, and the sum of available surface runoff and groundwater paleoclimate changes. A major focus of GISS GCM Physical Impacts of Climate Change on Water Resources 5 simulations is to study the human impact on the cli- investigate climate impacts as well as options for miti- mate, as well as the effects of a changing climate on gation and adaptation. One component of these new society and the environment. scenarios is a set of alternative futures of societal devel- opment known as the shared socioeconomic pathways FIO-ESM. The FIO Earth System Model7 is a GCM devel- (SSPs). The conceptual framework for the design and oped by the First Institute of Oceanography in China. It use of the SSPs calls for the development of global path- includes an ocean surface wave model in addition to ways describing the future evolution of key aspects of atmosphere, ocean, land, and ice components, and is society that would together imply a range of challenges coupled with a simulation model of the fully global car- for mitigating and adapting to climate change. bon cycle process and its interactions with the climate system. The historical simulation of the global carbon O’Neill et al. (2015) present the “SSP narratives,” a set of cycle follows the design of the CMIP5 (Climate Model five qualitative descriptions of future changes in demo- Inter-comparison Project Phase 5) long-term simula- graphics, human development, economy and lifestyle, tion experiments. The simulation results are used to 8 policies and institutions, technology, and environment evaluate the performance of the model, including the and natural resources. Development of the narratives atmosphere, ocean, land surface, and biogeochemical drew on expert opinion to identify key determinants of process of the ocean and terrestrial ecosystems. these challenges that were essential to incorporate in the narratives, and combine these elements in the nar- Shared Socioeconomic Pathways (SSPs) ratives in a manner consistent with their interrelation- Long-term scenarios play an important role in research on ships. The narratives are intended as a description of global environmental change. The climate change plausible future conditions at the level of large world research community is developing new scenarios inte- regions that can serve as a basis for integrated scenar- grating future changes in climate and society to ios of emissions and land use, as well as analyses of climate impact, adaptation, and vulnerability. ­ Figure 2. Shared Socioeconomic Pathways (SSPs) Within the conceptual framework for integrated sce- Representing Different Combinations of Challenges narios, the SSPs are designed to span a relevant range to Mitigation and Adaptation of uncertainty in societal futures. Unlike most global scenario exercises, the relevant uncertainty space that the SSPs are intended to span is defined primarily by SSP 5: SSP 3: the nature of the outcomes, rather than the inputs or (Mit. Challenges Dominate) (High Challenges) elements that lead to these outcomes. Therefore, the challenges for mitigation Fossil-fueled Regional Rivalry A Rocky Road SSP outcomes are specific combinations of socioeco- Socioeconomic Development Taking the Highway nomic challenges to mitigation and socioeconomic SSP 2: (Intermediate Challenges) challenges to adaptation. That is, the SSPs are intended Middle of the Road to describe worlds in which societal trends result in SSP 1: SSP 4: making mitigation of, or adaptation to, climate change (Low Challenges) (Adapt. Challenges Dominate) Sustainability Inequality harder or easier, without explicitly considering climate Taking the Green Road A Road Divided change itself. The SSPs used for this study are illus- trated in figure 2. Socioeconomic challenges for adaptation Figure 3 shows key assumptions made by the five SSPs Source: adapted from O’Neill et al. 2015. of future global population, GDP, and GDP per capita, 6 Physical Impacts of Climate Change on Water Resources Figure 3. Global Population, GDP, and GDP per capita Made by Each of the Five SSPs a. Global population 14,000,000 12,000,000 10,000,000 8,000,000 Thousands 6,000,000 4,000,000 2,000,000 0 30 40 70 80 50 60 90 10 20 00 15 05 25 35 45 55 65 75 85 95 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 21 Ref SSP1 SSP2 SSP3 SSP4 SSP5 b. Global GDP 500,000,000 450,000,000 400,000,000 350,000,000 Million 1990US$ 300,000,000 250,000,000 200,000,000 150,000,000 100,000,000 50,000,000 0 30 40 70 80 50 60 90 10 20 00 15 05 25 35 45 55 65 75 85 95 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 21 Figure continues next page Physical Impacts of Climate Change on Water Resources 7 Figure 3. continued c. Global GDP per capita 70,000 60,000 50,000 Thousands 1990US$/per 40,000 30,000 20,000 10,000 0 30 40 70 80 50 60 90 10 20 00 15 05 25 35 45 55 65 75 85 95 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 21 Ref SSP1 SSP2 SSP3 SSP4 SSP5 Note: Ref = reference scenario; SSP = Shared Socioeconomic Pathway. which were used as inputs for the GCAM simulations. suggests that the amount of surface water globally Table 1 summarizes socioeconomic data assumed by will remain practically fixed throughout the coming the SSPs. decades. Results and Discussion These results underscore a main message that fresh- Globally, total runoff volume is water is a finite resource with multiple uses, and thus Estimates of total annual run- confidently estimated to remain requires careful management with due consideration off volume for the three GCMs relatively constant throughout of issues of water quality and efficiency. used in this study are shown the 21 century. However, st in figure 4. This is the sum of While the total global runoff volume, an indicator of runoff is likely to decline substantially in some countries the runoff generated for the overall water availability may not vary significantly and regions, including Russia, 233 water basins around the over the next decades, there are some variations worth Central Asia, Central Africa, world in GCAM. The figure noting among regions and countries. and the Middle East. shows that the three different climate models agree that Map 2 displays estimated runoff depth around the there is not a significant trend (upward or down- world, as predicted by the three GCMs for the year ward) of the total runoff volume generated; this 2050 (maps showing changes to 2100 were generated, 8 Physical Impacts of Climate Change on Water Resources Table 1. Shared Socioeconomic Pathways as Implemented in GCAM SSP4 SSP1 SSP2 SSP3 Medium- SSP5 High-income Low-income income Socioeconomics Population in 2100 6.9 billion 9 billion 12.7 billion 0.9 billion 2.0 billion 6.4 billion 7.4 billion GDP per capita in 2100 $46,306 $33,307 $12,092 $123,244 $30,937 $7,388 $83,496 Fossil resources Coal Med/Low Med/Med High/High Med/Low Med/Med Med/High High/High (technological Conventional gas and oil Med/Med Med/Med Med/Med High/Low High/Low High/Low High/High change/acceptance) Unconventional oil Low/Med Med/Med Med/Med Med/Low Med/Low Med/Low High/High Electricity Nuclear High Med High Low Low Low Med (technology cost) Renewables Low Med High Low Low Low Med CCS High Med Med Low Low Low Low Fuel preference Renewables High Med Med High High High Med Traditional biomass Low Low High Low Low High Low Energy demand Buildings Low Med Low High Med Low High (service demands) Transportation Low Med Low High Med Low High Industry Low Med Low High Med Low High Agriculture and Food demand High Med Low High Med Low High land use Meat demand Low Med High Med Med Med High Productivity growth High Med Low High Med Low High Trade Global Global Global Regional Regional Local Global SPA policy Afforestation Limited No land afforestation policy Pollutant Emissions factors Low Med High High High High Low emissions Note: Med = medium; SPA = [Shared Policy Assumption]. but are excluded for brevity). Runoff depth, measured significant disagreement between the models on run- as total runoff divided by total land area, provides a off in South America, with two of the three (CCSM and better means of comparing runoff trends among coun- FIO) predicting relatively stable runoff patterns tries than measuring runoff in water volume because it throughout the continent, but GISS predicting extreme allows for large countries to be compared with smaller short falls in runoff in Brazil, Colombia, Ecuador, Peru, countries. Some trends can be summarized as follows: and República Bolivariana de Venezuela. • North America. There are no major variations in • Europe and Central Asia. There is a consistent trend runoff; the overall trend is for a small decrease in toward lesser runoff in all model simulations, with runoff in Canada and the United States, but some the Russian Federation showing a sharp decrease in simulations (CCSM and GISS) project small increases runoff in the second half of the century. for the United States by 2050. • East Asia. The runoff profile is relatively stable and • Central America. There is a consistent trend toward high (particularly in the Pacific). All simulations project diminishing runoff across all three models. There is runoff decreases in China. Two (CCSM and GISS) out of Physical Impacts of Climate Change on Water Resources 9 Figure 4. Estimates of Global Runoff Generation Using the CCSM, FIO, and GISS Climate Models 45,000 40,000 Total annual runo (billion m3/yr) 35,000 30,000 25,000 20,000 15,000 10,000 5,000 0 1975 2000 2025 2050 2075 2100 CCSM FIO ESM GISS Note: Global runoff generation reflects the sum for all countries. CCSM = Community Climate System Model; FIO-ESM = First Institute of Oceanography Earth System Model; GISS = Goddard Institute for Space Studies Model. Map 2. Change in Global Runoff by Country 2005–50 mm/year a. CCSM (Community Climate System Model) 1 60°W 1 40°W 1 20°W 1 00°W 80°W 60°W 40°W 20°W 0° 20°E 40°E 60°E 80°E 1 00°E 1 20°E 1 40°E 1 60°E 1 80° 80°N 80°N 60°N 60°N 40°N 40°N 20°N 20°N 0° 0° 20°S 20°S Legend Model: CCSM | Years: 2005–2050 Change in Runo (mm/yr) 40°S 40°S > –200 –200 60°S – –100 60°S –100 – 0 0 – +100 80°S 80°S +1001 80° – +200 1 60°W 1 40°W 1 20°W 1 00°W 80°W 60°W 40°W 20°W 0° 20°E 40°E 60°E 80°E 1 00°E 1 20°E 1 40°E 1 60°E > +200 Map continues next page 10 Physical Impacts of Climate Change on Water Resources Map 2. continued b. GISS (Goddard institute for space studies) model 1 60°W 1 40°W 1 20°W 1 00°W 80°W 60°W 40°W 20°W 0° 20°E 40°E 60°E 80°E 1 00°E 1 20°E 1 40°E 1 60°E 1 80° 80°N 80°N 60°N 60°N 40°N 40°N 20°N 20°N 0° 0° 20°S 20°S Legend 40°S 40°S Model: GISS | Years: 2005–2050 Change in Runo (mm/yr) 60°S 60°S < –200 –200 80°S – –100 80°S –100 1 80° – 0 1 60°W 1 40°W 1 20°W 1 00°W 80°W 60°W 40°W 20°W 0° 20°E 40°E 60°E 80°E 1 00°E 1 20°E 1 40°E 1 60°E 0 – +100 +100 – +200 > +200 c. FIO-ESM (First Institute of Oceanography Earth System Model) 1 60°W 1 40°W 1 20°W 1 00°W 80°W 60°W 40°W 20°W 0° 20°E 40°E 60°E 80°E 1 00°E 1 20°E 1 40°E 1 60°E 1 80° 80°N 80°N 60°N 60°N 40°N 40°N 20°N 20°N 0° 0° Legend 20°S 20°S Model: FIO | Years: 2005–2050 Change in Runo (mm/yr) 40°S 40°S < –200 –200 60°S – –100 60°S –100 – 0 – +100 080°S 80°S +100 1 80° – +200 1 60°W 1 40°W 1 20°W 1 00°W 80°W 60°W 40°W 20°W 0° 20°E 40°E 60°E 80°E 1 00°E 1 20°E 1 40°E 1 60°E > +200 Physical Impacts of Climate Change on Water Resources 11 the three climate model simulations in GCAM show a is more or less stable (but still in the low range, decreasing trend in runoff for Bangladesh, Cambodia, always below 200 mm/yr). Lao PDR, Myanmar, Thailand, and Vietnam. ­ eneration. • Africa. There is a greater variation of runoff g In the southern part of the continent, countries like • India. The results are mixed. Simulation results South Africa and Botswana show a consistent trend for  South Asia show runoff projections for India toward lesser runoff. Countries in the lower latitudes increasing during the second half of the century (20N to 20S) exhibit small variations in runoff when using the CCSM climate model as input. Using (less than +/- 100 mm/yr) in general. The GISS model the FIO as input results in a fairly stable runoff gen- input produces larger decreases in runoff toward the eration rate. Using GISS as climate model input second half of the century in the Central African results in a slight decrease in runoff for India as early Republic, the Democratic Republic of Congo, Malawi, as 2025 that continues in the second half of the Mozambique, Tanzania, Zambia, and Zimbabwe. century. • Middle East and North Africa. There is a consistent Projected Volumetric Inflow trend toward decreasing runoff to the lower runoff The rate of volumetric inflow into each country is pre- ranges. The Islamic Republic of Iran appears to be sented in map 3 for each of the climate models for the somewhat of an exception; its runoff generation rate year 2050. Volumetric inflow accounts for streamflow Map 3. Inflow Distribution by Country, 2050 (km3/year) a. CCSM (Community Climate System Model) 160°W 140°W 120°W 100°W 80°W 60°W 40°W 20°W 0° 20°E 40°E 60°E 80°E 100°E 120°E 140°E 160°E 180° 180° 80°N 80°N 60°N 60°N 40°N 40°N 20°N 20°N 0° 0° 20°S 20°S Legend 40°S 40°S Model: CCSM | Year: 2050 Inflow (km3/yr) 60°S 60°S 0.00–10.00 10.01–50.00 50.01–100.00 80°S 80°S 100.01–200.00 180° 160°W 140°W 120°W 100°W 80°W 60°W 40°W 20°W 0° 20°E 40°E 60°E 80°E 100°E 120°E 140°E 160°E 180° 200.01–500.00 500.01–1000.00 1000.01–2000.00 >2000 Map continues next page 12 Physical Impacts of Climate Change on Water Resources Map 3. continued b. GISS (Goddard Institute for Space Studies) Model 160°W 140°W 120°W 100°W 80°W 60°W 40°W 20°W 0° 20°E 40°E 60°E 80°E 100°E 120°E 140°E 160°E 180° 180° 80°N 80°N 60°N 60°N 40°N 40°N 20°N 20°N 0° 0° 20°S 20°S Legend GISS | Year: 2050 Model: 40°S 40°S Inflow (km3/yr) 0.00–10.00 60°S 60°S 10.01–50.00 50.01–100.00 100.01–200.00 80°S 80°S 200.01–500.00 180° 160°W 140°W 120°W 100°W 80°W 60°W 40°W 20°W 0° 20°E 40°E 60°E 80°E 100°E 120°E 140°E 160°E 180° 500.01–1000.00 1000.01–2000.00 >2000 c. FIO-ESM (First Institute of Oceanography Earth System Model) 160°W 140°W 120°W 100°W 80°W 60°W 40°W 20°W 0° 20°E 40°E 60°E 80°E 100°E 120°E 140°E 160°E 180° 180° 80°N 80°N 60°N 60°N 40°N 40°N 20°N 20°N 0° 0° 20°S 20°S Legend Model: FIO | Year: 2050 40°S 40°S Inflow (km /yr) 3 0.00–10.00 60°S 60°S 10.01–50.00 50.01–100.00 100.01–200.00 80°S 80°S 200.01–500.00 180° 160°W 140°W 120°W 100°W 80°W 60°W 40°W 20°W 0° 20°E 40°E 60°E 80°E 100°E 120°E 140°E 160°E 180° 500.01–1000.00 1000.01–2000.00 >2000.00 Physical Impacts of Climate Change on Water Resources 13 in rivers crossing from one country to another, plus The Socioeconomic Impacts of Future the contribution of groundwater ­ storage within a Development Scenarios on Water Scarcity basin (or country). Because of this, inflow is more of a In order to determine the socioeconomic impacts of hydraulic process than a hydrologic one. This means future development scenarios on water scarcity, both that the inflow flux is driven more by land surface fea- the future supply and demand of water are estimated tures (such as soil type, land use, geology, and geo- and compared, to determine regions where water morphology) than by climate (which has a primary scarcity may arise. Hydrologic inputs (supply) into influence on the rate of runoff generation through its the WSI calculation (runoff and inflows) come from relationship with rainfall and temperature); thus the the three GCMs used in the prior section, while water results for inflow into countries show lesser depen- demands are dictated by the SSP scenarios simulated. dence on the climate model used. These water demands are summarized in figure 5, broken down by water demand sector. SSP1 results in Projected Water Scarcity a curbing of water demand starting in the year 2050, business-as-usual) scenario for Finally, the reference (­ and the decrease occurs across all demand sectors. these GCAM simulations is used to portray the current SSP2 results show an increase in water demand fol- and future status of water stress/scarcity around the lowed by  a plateau toward 2070 and a very slight climate mitigation world without the introduction of ­ decrease in  water demand across all sectors toward ­policies. Map 4 shows the sim- the end of the simulation period in 2095. SSP3 results ulation results for the Water show, as  expected, a continuous increase in water Global trends in water Scarcity Index (WSI) in the ref- demand across all sectors, with particular strong demand and water scarcity erence scenario, comparing ­rrigation water use. SSP4 results shows a growth in i will be strongly affected by years 2005, 2025, 2050, and water demand that plateaus starting in 2060, a similar socioeconomic factors, with a 2095. trend to that found in SSP2. However, SSP4 stabilizes significant majority of water at lower  ­ values than those in SSP2, reflecting the going to irrigated agriculture. These results illustrate three lesser energy generation and use of water in SSP4; key trends in the WSI. First, increased efforts  for mitigation reduce the pressure there is a general trend upward in water scarcity in the over water resources. majority of countries of the world; this is reasonable to expect given increased pressure in water resources (increased demand) as a result of population growth, This effect is further illustrated in figure 6, which development, and other factors. Second, the WSI ­displays total global water demand across the five results appear to be fairly consistent across the three SPs, as well as water demand for three select sectors: climate models used; this suggests that water scarcity agriculture, electricity, and municipal use. Starting is dominated by water demands rather than by the with total water use, the image shows that there is a climate-influenced water availability (surface and ­ very large plausible range of water demand by groundwater). Finally, it appears that severe and mod- 2100, ranging from 4,500 billion km3/year for SSP1 to erate water scarcity around the world will increase sig- 6,500 billion km3/year for SSP3 and SSP5. This implies nificantly within the next few decades (between 2025 that future global demand for water is highly depen- and 2050), particularly in countries such as China, dent on socioeconomic factors. For irrigation, the India, and Mexico, and the Middle East and North range is much tighter between the five SSPs, implying Africa (MENA) region. that socioeconomic factors will not play a large role in 14 Physical Impacts of Climate Change on Water Resources Map 4. Water Scarcity Indicator per Country a. 2005 and 2025 CCSM FIO GISS b. 2050 and 2095 CCSM FIO GISS No scarcity Low scarcity Moderate scarcity Severe scarcity Note: CCSM = Community Climate System Model; FIO = First Institute of Oceanography Earth System Model; GISS = Goddard Institute for Space Studies Model. Physical Impacts of Climate Change on Water Resources 15 Figure 5. Water Demand (Global Water Withdrawal) for the Five SSPs and Broken Down by Major Water-using Sectors billion m3/year SSP5 SSP3 7,000 7,000 Global water withdrawal Global water withdrawal 6,000 6,000 5,000 5,000 (billion m3/yr) (billion m3/yr) 4,000 4,000 3,000 3,000 2,000 2,000 1,000 1,000 0 0 20 5 20 5 05 25 20 5 45 20 5 65 20 5 85 95 05 25 20 5 45 20 5 20 5 20 5 20 5 95 1 1 3 5 7 3 5 6 7 8 20 20 20 20 20 20 20 20 20 20 Socioeconomic challenges for mitigation SSP2 7,000 Global water withdrawal 6,000 5,000 (billion m3/yr) 4,000 3,000 2,000 1,000 0 20 5 05 25 20 5 65 20 5 85 95 20 5 20 5 1 3 4 5 7 20 20 20 20 20 SSP1 SSP4 7,000 7,000 Global water withdrawal Global water withdrawal 6,000 6,000 5,000 5,000 (billion m3/yr) (billion m3/yr) 4,000 4,000 3,000 3,000 2,000 2,000 1,000 1,000 0 0 20 5 20 5 25 05 20 5 45 20 5 65 20 5 85 95 05 25 20 5 45 20 5 20 5 20 5 85 95 1 1 3 5 7 3 5 6 7 20 20 20 20 20 20 20 20 20 20 20 Socioeconomic challenges for adaptation Municipal Primary energy Manufacturing Electricity Livestock Irrigation Note: SSP = Shared Socioeconomic Pathway. determining agricultural water use. Global water use the year 2100. This is driven mostly by the assumption for electricity generation, on the other hand, shows of a much larger size of the economy implicit in SSP5. a  very large spread between SSP1 and SSP5, with a The relationship between the SSPs and the key water-us- nearly 300 percent increase in water withdrawal ing sectors—energy and food—is illustrated in figure 10. predicted for the latter scenario over the f ­ ­ormer by 16 Physical Impacts of Climate Change on Water Resources Figure 6. Water Demand (Global Water Withdrawal) across Five SSPs, by Sector a. Total global water demand b. Irrigation agriculture 8,000 4,500 7,000 4,000 3,500 6,000 3,000 5,000 2,500 km3/yr km3/yr 4,000 2,000 3,000 1,500 2,000 1,000 1,000 500 0 0 15 15 05 25 35 45 55 65 75 85 95 05 25 35 45 55 65 75 85 95 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 Ref SSP1 SSP2 SSP3 SSP4 SSP5 c. Electricity d. Municipal 900 1,000 800 900 700 800 700 600 600 500 km3/yr km3/yr 500 400 400 300 300 200 200 100 100 0 0 15 05 25 35 45 55 65 75 85 95 15 05 25 35 45 55 65 75 85 95 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 Ref SSP1 SSP2 SSP3 SSP4 SSP5 Note: Ref = reference scenario; SSP = Shared Socioeconomic Pathway. Global generation of electricity tends to follow a similar first century. However, as figure 6 shows, the twenty-­ pattern to that of the water demand for electricity shown SSP1 predicts significantly less water consumption in in figure 6. The levels of energy production is signifi- the electricity sector than the other SSPs. Water demand cantly greater in SSP5 than in the other four scenarios, for global food production tapers off and then declines again because of the assumption of a much larger econ- in all scenarios (SSP1 and SSP5 circa 2050, SSP2 and SSP4 omy. It is interesting to note that SSP1, SSP3, and SSP4 all circa 2070) except for SSP3. This is mostly consistent predict similar ­ levels of energy production throughout with the irrigation water use trends shown in Figure 6. Physical Impacts of Climate Change on Water Resources 17 Figure 7. Energy and Food Production at the Global Scale for the Different SSPs a. Global electricity generation b. Food production (crops) 400 12,000 350 10,000 300 8,000 250 Pca/yr EJ/yr 200 6,000 150 4,000 100 2,000 50 0 0 15 05 25 35 45 55 65 75 85 95 15 05 25 35 45 55 65 75 85 95 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 Ref SSP1 SSP2 SSP3 SSP4 SSP5 Note: Ref = reference scenario; SSP = Shared Socioeconomic Pathway. Projected Effects of Mitigation Policies climate change mitigation policy (6.0 W/m2) and not ­ (4.5  W/m2) is not large enough to result in a signifi- Finally, two simulation scenar- cant difference in total water supply. As in the results Simulations show that ios are compared to determine for the no mitigation policy case, implementing a cli- mitigation policies that the potential effects that miti- mate policy with RCP4.5 does not result in a signifi- reduce greenhouse gas gation policies may have on cant trend (upward or downward) of the total runoff concentrations throughout future water scarcity. Under the volume generated, suggesting that the amount of sur- the 21st century will have “no mitigation policy” scenario face water globally remains practically fixed through- little impact on water scarcity. (SSP1) water demand follows a out the coming decades. Map 5 displays the spatial trajectory that reaches 6.0 W/m2 distribution of runoff depth around the world under a in 2100, while water supply is calculated using climate climate mitigation policy, showing some variations scenario RCP6.0. Under a “mitigation policy” scenario worth noting among regions and countries. (SSP1 with a mitigation policy), water demand follows a trajectory that reaches 4.5 W/m2 in 2100, while water When there are no constraints on water demands, the supply is calculated using climate scenario RCP4.5. results represent a response to changes only in demand Figure 8 shows the estimates of total annual runoff and energy from the mitigation policy put in place. volume for the three GCMs used in this study, under Since SSP1 is a sustainable scenario—and without a cli- a  climate mitigation policy scenario. When these mate policy the radiative forcing is 6.0 W/m2, while results are compared to those presented in figure 4 with the policy it is 4.5 W/m2—the difference in forcing for the GCAM reference scenario, the global amount is not large enough in this scenario and the results do of runoff generated is practically the same. The differ- not show a dramatic difference in total water demand ence in radiative forcing between implementing a (figure 9). 18 Physical Impacts of Climate Change on Water Resources Figure 8. Estimates of Global Runoff Generation using the CCSM, FIO, and GISS Climate Models under a Climate Mitigation Policy billion m3/year 45,000 40,000 35,000 30,000 Total annual runoff 25,000 20,000 15,000 10,000 5,000 0 1975 2000 2025 2050 2075 2100 CCSM FIO ESM GISS Note: The estimates include the sum for all countries. CCSM = Community Climate System Model; FIO-ESM = First Institute of Oceanography Earth System Model; GISS = Goddard Institute for Space Studies Model. Map 5. Distribution of Changes in Global Runoff by Country, under a Climate Mitigation Policy, Projected using Climate Models CCSM, GISS, and FIO, Year 2050, mm/year a. CCSM (Community Climate System Model) 160°W 140°W 120°W 100°W 80°W 60°W 40°W 20°W 0° 20°E 40°E 60°E 80°E 100°E 120°E 140°E 160°E 180° 180° 80°N 80°N 60°N 60°N 40°N 40°N 20°N 20°N 0° 0° 20°S 20°S Legend CCSM | Year: 2050 Model: 40°S 40°S Runoff (mm/yr) 0.00–50.00 60°S 60°S 50.01–100.00 100.01–200.00 200.01–300.00 80°S 80°S 300.01–500.00 180° 160°W 140°W 120°W 100°W 80°W 60°W 40°W 20°W 0° 20°E 40°E 60°E 80°E 100°E 120°E 140°E 160°E 180° 500.01–700.00 700.01–1000.00 >1000 Map continues next page Physical Impacts of Climate Change on Water Resources 19 Map 5. continued b. GISS (Goddard Institute for Space Studies) Model 160°W 140°W 120°W 100°W 80°W 60°W 40°W 20°W 0° 20°E 40°E 60°E 80°E 100°E 120°E 140°E 160°E 180° 180° 80°N 80°N 60°N 60°N 40°N 40°N 20°N 20°N 0° 0° 20°S 20°S Legend GISS | Year: 2050 Model: 40°S 40°S Runoff (mm/yr) 0.00–50.00 60°S 60°S 50.01–100.00 100.01–200.00 200.01–300.00 80°S 80°S 300.01–500.00 180° 160°W 140°W 120°W 100°W 80°W 60°W 40°W 20°W 0° 20°E 40°E 60°E 80°E 100°E 120°E 140°E 160°E 180° 500.01–700.00 700.01–1000.00 >1000 c. FIO-ESM (First institute of oceanography earth system model) 160°W 140°W 120°W 100°W 80°W 60°W 40°W 20°W 0° 20°E 40°E 60°E 80°E 100°E 120°E 140°E 160°E 180° 180° 80°N 80°N 60°N 60°N 40°N 40°N 20°N 20°N 0° 0° 20°S 20°S Legend FIO | Year: 2050 Model: 40°S 40°S Runoff (mm/yr) 0.00–50.00 60°S 60°S 50.01–100.00 100.01–200.00 200.01–300.00 80°S 80°S 300.01–500.00 180° 160°W 140°W 120°W 100°W 80°W 60°W 40°W 20°W 0° 20°E 40°E 60°E 80°E 100°E 120°E 140°E 160°E 180° 500.01–700.00 700.01–1000.00 >1000 Note: CCSM = Community Climate System Model; FIO-ESM = First Institute of Oceanography Earth System Model; GISS = Goddard Institute for Space Studies Model. 20 Physical Impacts of Climate Change on Water Resources Figure 9. Global Water Withdrawal under SSP1 in Mitigation Policy and a No Mitigation Policy Scenarios a. With mitigation policy 6000 5000 Global water withdrawal (billion m3/yr) 4000 3000 2000 1000 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 b. Without mitigation policy 6000 Global water withdrawal (billion m3/yr) 5000 4000 3000 2000 1000 0 70 80 90 10 20 30 40 50 60 55 65 75 85 95 05 25 35 15 45 00 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 21 USA Russia Europe_Non_EU Canada Taiwan Pakistan Europe_Eastern Brazil Southeast Asia Middle East EU-15 Australia_NZ South Korea Mexico EU-12 Argentina South Asia Japan Colombia Africa_Western South America_Southern Indonesia China Africa_Southern South America_Northern India Central Asia Africa_Northern South Africa European Free Trade Central America and Africa_Eastern Association Caribbean Note: SSP = Shared Socioeconomic Pathway. Physical Impacts of Climate Change on Water Resources 21 Figure 10. Difference in Global Water Withdrawal under SSP1 between Mitigation Policy and No Mitigation Policy Scenarios for the 32 GCAM Regions 80 Africa_Eastern Africa_Northern Africa_Southern Africa_Western Argentina 60 Australia_NZ Brazil Canada Di erence in regional water withdrawal (billion m3/yr) Central America and Caribbean Central Asia 40 China Colombia EU-12 EU-15 Europe_Eastern 20 Europe_Non_EU European Free Trade Association India Indonesia Japan 0 Mexico Middle East Pakistan Russia South Africa –20 South America_Northern South America_Southern South Asia South Korea Southeast Asia Taiwan –40 2000 2050 2100 USA Note: Difference = No mitigation policy (Reference) – Mitigation policy. EU = European Union. Global water withdrawals actually decrease slightly Conclusion with the mitigation policy implemented, but some This paper documents an initial study focused on regions of the world decrease while others increase, as understanding the physical impacts of climate change is shown in figure 10. China and India see significant on water resources throughout the world. The research increases in water use as a result of the mitigation pol- performed in this paper is based on the application of icy, while the rest of South Asia (excluding India), an IAM (GCAM) to quantify these impacts for a wide Western Africa, much of North America (Mexico, range of scenarios of socioeconomic development that United States), and Central America and the Caribbean offer a mix of possible futures for the availability, use, see the largest decreases in water withdrawal. 22 Physical Impacts of Climate Change on Water Resources and management of water resources. The understand- global water withdrawals, but some regions of the ing gained through this analysis is expected to contrib- world decrease while others increase. ute to the ongoing dialogue on the sustainability of Data on future projections of water supply and demand multiple human activities and their trajectories toward for different climate and socioeconomic development global development pathways. scenarios generated through this study need to be val- idated at the regional and country levels so they can Through this research and analysis, this study pro- provide reliable intelligence for purposes of water vides an integrated qualitative and quantitative resources assessment and management. understanding of the implications of several selected issues, including climate change and mitigation, IAMs such as GCAM provide a quantitative economic socioeconomic and technological developments on framework for an integrated analysis of water supply water scarcity, and water-energy-food interactions in and demand, multiple demand sectors, climate inputs, a global context. and other forcing factors such as land use change, policy interventions, and technological developments. ­ A key message that follows from these results is that, These models provide a viable tool to explore addi- at a global scale, the rate of runoff generation will not tional issues related to the water-energy-food nexus. vary significantly over this century. These results Further research can be focused on such issues as the reinforce the notion that freshwater is a finite implications of groundwater availability and changes in resource with multiple uses, requiring careful man- pumping costs on future water supply and its effect on agement with due consideration of issues of water urban services, energy, and food security; the repercus- quality and efficiency. While the global runoff vol- sions of removing existing distortions (subsidies) in ume may not vary significantly over the coming water availability and distribution in the future; the decades some variations are worth noting among economic costs of noncooperation across basins/coun- regions and countries. tries/regions and the potential benefits of cooperation; Simulation results show a general upward trend in quantifying trade-offs in water availability and its water scarcity in the majority of the world’s countries; impact on major economic sectors; defining effective this is reasonable to expect given increased pressure adaptation strategies/investments that are necessary to on water resources (increased demand) as a result of mitigate the impact of climate change on water scarcity population growth, development, and other factors. and stress; and identifying and planning key invest- These Water Scarcity Index results appear to be fairly ments at regional and country levels to address eco- consistent among the three climate models used, sug- nomic water scarcity. gesting that water scarcity is dominated by water demands rather than by the climate-influenced water Notes availability (surface and groundwater). Severe and 1. http://www.globalchange.umd.edu/models/gcam. moderate water scarcity around the world is likely to advance significantly between 2025 and 2050, in coun- 2. GCAM is a publicly available, open source modeling tool, developed and  maintained by the Pacific Northwest National Laboratory, part tries and regions where water is already somewhat of  the US Department of Energy. It is available at http://www​ scarce, such as China, India, Mexico, and the Middle .­globalchange​.umd.edu/models/gcam/download/. Further details East and North Africa. about GCAM can be found on its wiki site: https://wiki.umd.edu/gcam. 3. CCSM = Community Climate System Model; FIO-ESM = First Institute Implementing climate change mitigation policies of Oceanography Earth System Model; GISS = Goddard Institute for (emissions reduction) results in a slight decrease in Space Studies Model. Physical Impacts of Climate Change on Water Resources 23 4. http://www.fao.org/nr/water/aquastat/main/index.stm. 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