The Human Thirst for Water Under Global Change: What and where are the Future Risks?

The future of water availability and security is of paramount importance. A climacteric challenge toward the future sustainability of this precious resource is to identify where and when water may become substantially limited in the coming decades and what are the key drivers. The sustainability of water resources are affected by many factors that include: population, wealth, energy, land use, as well as climate. Yet, prediction systems are challenged by uncertainties in models and observational support as well as the practical and theoretical limits-to-prediction of the Earth's systems. This limits any one forecast of a potential future as actionable information - and the scientific community has moved toward risk-based assessments to provide a likelihood of outcomes - to the fullest extent possible.

We present a synopsis of recently published and ongoing analyses from experiments with the MIT Integrated System Model (IGSM) linked to a Water Resource System (WRS). These experiments address the future of water stress in a global context as well as with regional lenses over the United States and a large portion of Southern and Eastern Asia. By 2050, global economic growth and population change can lead to an additional 1.8 billion people living under at least moderate water stress, with 80% located in developing countries. Combined, socioeconomic growth and uncertain climate change lead to a 1.0–1.3 billion increase of the world’s 2050 projected population living with overly exploited water conditions—where total potential water requirements will consistently exceed surface water supply. Using a large ensemble of scenarios that are consistent across economics, emissions, climate, population, etc., we develop risk portfolios of water stress over a large portion of Asia (Figure 1) and isolate the effects of socioeconomic growth (population and wealth) and climate change. We find the number of people under water stress more than doubles from about 800 million to 1.7 billion by 2050. These insights point to needed actions to adapt and protect future water supplies. Further experimental simulations are presented to demonstrate the utility of widespread adaptive measures that include: enhanced storage and transfer as well as water-use efficiency and reduced consumption.