GCAM v4.3 SSP-RCP-GCM Output Databases

This analysis makes deterministic classifications of how, when water resources are limited and constrained, the human and climate systems interact. The relative effects of both systems on water scarcity are quantified at global and basin scales across 15 global futures that include five different socioeconomic conditions (the Shared Socioeconomic Pathways, SSPs) and four different climatic conditions (the Representative Concentration Pathways, RCPs). These 15 scenarios are used to first analyze a 'Human Alone' component by isolating the human impact on future scarcity. This is accomplished by holding all climate variables to their 2005 levels while altering socioeconomic growth and technological change. General circulation model (GCM) derived climate impacts for five models are applied to establish 75 'Human and Climate' scenarios which allows for the quantification of climate impacts. Climatic impacts to water supply, agricultural productivity and change, hydropower availability, and building energy demands are applied from 5 different bias-corrected GCMs to make a suite of 75 climate runs. By subtracting the human derived impacts from the 'Human Alone' scenarios, from the 'Human and Climate' scenarios the climate impact is isolated. First, the drivers of future water scarcity are evaluated by isolating the impacts that both humans and climate have while accounting for feedbacks between humans, energy, and land. Secondly, the simultaneous impacts that human and climate systems have on water scarcity are analyzed by determining whether each system is increasing or decreasing scarcity in all global water basins. We describe the GCAM model, the scenario components, climate derived impacts, and the calculations of scarcity changes and attribution. This study uses the global change assessment model (GCAM), with inclusions of water constraints to both renewable and nonrenewable sources of water, to investigate the relative contributions of climate and human systems on water scarcity regionally and globally under a wide range of scenarios. GCAM links socioeconomics, the energy system, land-use change, climate, and the water sector. GCAM is a market-equilibrium model that allows for prices to be adjusted within each time step to ensure that the supply and demand of goods and services remains equilibrated at each time step allowing for simultaneous market clearing across sectors. This study accounts for a limited supply of water by employing cost resource curves across all 235 basins that follow a logit formulation to determine the share of each water source (renewable surface water, nonrenewable groundwater, and desalinated water) needed to meet the water demands within all basins. As depletion of various water sources increases the extraction price increases, which leads to compounding price increases on the goods and services that require higher-priced water sources.

本分析针对水资源受限约束的情境下，人类系统与气候系统的相互作用模式开展确定性分类判定。本研究在全球及流域尺度下，针对涵盖5种社会经济情景（共享社会经济路径，Shared Socioeconomic Pathways, SSPs）与4种气候情景（典型浓度路径，Representative Concentration Pathways, RCPs）的15个全球未来情景，量化了两类系统对水资源短缺的相对影响。这些15个情景首先被用于分析“仅人类影响”组分，即通过剥离人类对未来水资源短缺的影响来实现：具体做法是将所有气候变量固定在2005年水平，同时改变社会经济增长与技术变革轨迹。研究选取5个通用环流模式（General Circulation Model, GCM）的气候影响结果，构建75个“人类与气候共同影响”情景，以此实现气候影响的量化分析。采用5种经过偏差校正的GCM，将气候对供水、农业生产力及变化、水电可获得性以及建筑能源需求的影响纳入其中，形成75组气候驱动模拟集合。通过从“人类与气候共同影响”情景中减去“仅人类影响”情景下的人类驱动影响，即可剥离得到气候系统的单独影响。首先，本研究通过剥离人类与气候的各自影响，同时考虑人类、能源与土地系统间的反馈机制，评估未来水资源短缺的驱动因素；其次，通过判定全球所有流域内人类与气候系统分别是加剧还是缓解水资源短缺，分析两类系统对水资源短缺的协同影响。本研究详细阐述了全球变化评估模型（Global Change Assessment Model, GCAM）、情景组分、气候驱动影响以及水资源短缺变化与归因的计算方法。本研究采用GCAM，纳入可再生与非可再生水资源的约束条件，旨在探究多种情景下气候与人类系统对全球及区域水资源短缺的相对贡献。GCAM实现了社会经济系统、能源系统、土地利用变化、气候系统与水资源部门的耦合联动。GCAM属于市场均衡模型，允许在每个时间步长内调整价格，确保各时段内商品与服务的供需保持均衡，实现跨部门市场的同时出清。本研究针对235个流域采用遵循logit公式的成本资源曲线以核算有限水资源供给：通过该曲线确定各流域内满足用水需求所需的各类水源（可再生地表水、非可再生地下水以及淡化水）的占比。随着各类水源的枯竭，取水成本不断攀升，进而推高依赖高成本水源的商品与服务的价格，形成价格叠加上涨效应。