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Sustaining the water supply in megacities is an enormous challenge. To address this challenge, it is especially important to predict water demand changes in megacities. This paper presents a system dynamics model to predict the future water demands of different sectors considering multiple factors, including population, structure of the economy, and water supply and use technologies. Compared with traditional methods such as the time series method and structure analysis method, the proposed model takes into account the interconnections, non-linear relationships and feedbacks between the various factors in a systems context. The model is applied to Beijing, a megacity with a population over 20 million and very limited water availability. It is found that the total water demand is likely to increase by at least 36.1% (up to 62.5%) by 2030 compared with that in 2011, and the water deficits vary from -0.36 × 109 to 1.80 × 109m3 in 2030. In addition, scenarios are designed to account for impacts associated with economic development, climate change and inter-basin water transfers. It is shown that climate change may have a large impact on the water supply reliability in Beijing. The water shortage problems can be alleviated via inter-basin water transfers. [ABSTRACT FROM AUTHOR]

Options for adapting to changing water resources' availability due to climate change have been routinely assessed for ability to alleviate expected impacts. Methods for evaluating effectiveness of adaptation options are usually based on, fundamentally different but complementary, hazards and vulnerability assessment based approaches. In this paper, we describe a framework to integrate these approaches for improved climate change adaptation policy making. We further review assessment approaches and corresponding criteria used for evaluation of planned adaptation options in the water sector. A synthesis of methods for evaluation reveals four main categories: (i) natural sciences based, (ii) social sciences based, (iii) overlapping and (iv) trans-disciplinary. Criteria from reviewed studies are classified using a scale vis-à-vis theme based classification, and unified into a criteria set covering important adaptation requirements while allowing case-specific modification. We find that important criteria, such as temporal scope of adaptation and implementability, have not been explicitly considered in scientific literature. The type of adaptation has an important bearing on evaluation and should be effectively modelled to make an informed decision regarding performance. Moreover, we suggest that it is important to explicitly consider influence of future changes in non-climatic factors along with climatic changes for a more robust analysis. [ABSTRACT FROM AUTHOR]

This paper aims to propose a decision support system (DSS) for evaluating the climate change impacts on water supply-demand and inundation; and assessing the risks for water shortage and inundation under future scenarios. The proposed DSS framework is universal and flexible, which comprises five modules integrated by a geographic information system platform, including the modules of (1) scenario rainfall and temperature projection under climate change, (2) impact assessment of water supply-demand, (3) impact assessment of inundation, (4) assessment of vulnerability and risk, and (5) adaptation strategy. A case study in southern Taiwan was performed to demonstrate how the DSS provides information on the climate change impacts and risks under future scenarios. The information is beneficial to the authorities of water resources management for understanding the spatial risks for water shortage and inundation, and planning suitable adaptation strategies for the locations with larger risks. [ABSTRACT FROM AUTHOR]