Water Resources in the 21st Century

A Policy Statement of the American Meteorological Society
(Adopted by AMS Council on 30 May 2017)

The provision of adequate fresh-water resources for people and ecosystems will be one of the most critical and potentially contentious issues facing society and governments at all levels during the 21st century. Water is fundamental for all life on Earth — for agriculture, energy production, sanitation, ecosystem health, transportation, and recreation. Yet, the demands upon water resources are ever increasing from population growth and migration, land use changes, and pollution on the local, national, and global levels — problems likely to be exacerbated over the next several decades by hydrologic change.

UN-Water, 2013, defines water security as “the capacity of a population to safeguard sustainable access to adequate quantities of acceptable quality water for sustaining livelihoods, human well-being, and socio-economic development, for ensuring protection against water-borne pollution and water-related disasters, and for preserving ecosystems in a climate of peace and political stability.” As such, we understand that water security is a leading element of U.S. National Security.

In light of these challenges, the American Meteorological Society (AMS) issues this statement and is committed to work with public,  commercial, and academic organizations at all levels, and seeks the support of the Congress, the Administration, and international partners in pursuing sustainable solutions. The broader water resource community must be engaged with the atmospheric science community using collaborative and integrative methods to identify key priorities and to meet information needs. Two grand challenges are identified below.

Quantifying and Adapting to Hydrologic Change

Hydrologic Change is the combined result of climate change and human modifications of the water cycle including local- to regional-scale water management and uses and landscape change. These influences introduce both variability over time and long-term trends by altering the statistical properties of key hydrologic variables, from surface water to deep aquifers, on multiple timescales.

It is increasingly clear that traditional water planning approaches, developed under the assumption of hydrologic stationarity, are no longer adequate. Current (and projected) levels of hydrologic change severely diminish the value of the historical hydrologic record as a guide to what the future may hold. Further complexity is added when balancing multiple and changing human and environmental demands.

New approaches to incorporating information about water-related risks will be needed to support adaptation. The AMS community can contribute by providing insights on the likelihood of near-term extreme weather as well as water resource impacts that will result from hydrologic changes. Given that precipitation is a primary forcing in hydrologic models, an increased focus on improving quantitative precipitation forecasts is needed;  improving the reliability of short-term to seasonal hydrologic forecasts, through better computational and data resources, and new space- and ground-based observations must also be a priority.  

The capacity to project the hydrologic impacts of anthropogenic climate change at spatial scales important for water resource management remains limited. Current global climate models cannot explicitly resolve many hydrologically important processes including orographic or convective precipitation and most land surface feedbacks. However, improved regional projections from statistical or physically based downscaling techniques and the development of higher resolution global climate models are helping to clarify the uncertainties surrounding future hydrologic change and to quantify plausible scenarios of climate change impacts.

Planning under Multifaceted Uncertainty

Emerging hydrologic and socioecological changes lead to a high degree of uncertainty regarding the future of hydrologic systems and human and ecological impacts, creating a need for new water resource management strategies. Planning activities now need to incorporate adaptive risk management as a response to large and persistent uncertainties.

An emerging paradigm shift in water resource planning gives explicit attention to the robustness of management options under uncertainty. One approach adopts a structured decision-making framework, which focuses on quantitatively identifying options that will perform adequately under a broad range of plausible future conditions, while meeting the need to incorporate flexibility when designing long-lived infrastructure or negotiating operating agreements. Flexibility can involve designs that reduce the costs of future modifications, or simply that are engineered to avoid catastrophic failure. 

To be effective, robust planning requires a sound understanding of what is and is not known about future hydrologic change at specific locations. The AMS community can contribute by identifying hydrologic scenarios that adequately represent both natural variability and climate change uncertainties, while the water management community can provide guidance on the relevance of those efforts. A two-way exchange between the atmospheric science and water resource management communities will allow mutual learning and close collaborative exploration of potential solutions. This coupling and synthesizing of comprehensive interdisciplinary scientific information will be critical for successful planning and adaptations in the 21st Century.


  • Water resources may be one of the greatest sources of contention in the 21st century, and emerging hydrologic spatiotemporal variabilities and trends will exacerbate many of those disagreements.
  • Water resources challenges from changes in climate, land cover, and water management are unavoidable, and require increased coordination between atmospheric scientists, engineers, hydrologists, and the broader resource community.
  • Research efforts focused on revealing, quantifying, and — where possible — reducing climate and hydrologic uncertainties can inform and support water resources policy-making, planning, and management.
  • Living with uncertainty requires flexible engineering and adaptive risk management practices and policies that can help us to realize assured long-term sustainability.
  • The large reservoir of scientific expertise and energy that the AMS membership comprises can be key to meeting many of these challenges.



[This statement is considered in force until May 2022 unless superseded by a new statement issued by the AMS Council before this date.]