What is water security and how is it impacted by climate change?

What is water security?

Water is essential to humans’ everyday existence and for a range of economic activities in rural, urban and industrial contexts. Yet access to water varies dramatically, from simply turning on a nearby tap to needing to walk, queue for and carry water, sometimes over long distances. Water can also be a threat: poor water quality can make people seriously ill, while floods are among the most damaging and deadly climate-related hazards.

The Sustainable Development Goal on water articulates the global aspiration to ‘ensure availability and sustainable management of water and sanitation for all’. However, this goal is far from being achieved and 771 million people globally lack basic access to clean drinking water. 

All of these aspects of water are encompassed in the concept of water security. Definitions generally include the need for a reliable supply of clean, safe water in the context of variability that is being exacerbated by climate change (e.g. changes to precipitation patterns), problems with water supply systems, and competition over access to water. Water security also means an acceptable level of protection against flooding (or water-related hazards more broadly) and consideration of water’s role in supporting healthy ecosystems such as maintaining water levels for wildlife in wetlands habitats.

An essential feature of water security is the recognition of profound interconnections between the physical (hydrological) and social systems around water resources – in other words, that human activities both shape and are shaped by water systems. Addressing these physical and human dimensions together is vital to making progress on water security as safe amounts of good quality water need to be present and reliably accessible to all. Accessibility requires effective provision, allocation, management and pricing of water resources – all of which are strongly influenced by social and political values. 

Maintaining and improving water security represents a set of major, cross-cutting challenges. This was recognised at the 2023 UN Water Conference: “Adding to the pressure, more than 90% of disasters are water-related, with climate change hitting hardest through water”. However, making climate-resilient progress on water security to secure safe water for all requires sustained political and public attention, alongside more finance and approaches to water management that consider the needs of all types of users.

What does climate change mean for the water cycle and water security?

Climate change is occurring as a complex mix of slow onset trends such as warming, changes in variability or fluctuations in conditions (whereby places become on average wetter or drier), and changes in the frequency and intensity of extreme events. Many of the most significant environmental and societal effects are likely to manifest through impacts on the hydrological (water) cycle and, in turn, on water security.

Changes in the timing, amount, intensity and state of precipitation (as snowfall or rainfall), and in atmospheric evaporative demand (the potential loss of water from the Earth’s surface, driven by atmospheric factors), will alter the availability of surface and groundwater sources. The characteristics of the land’s surface, including land use and land cover – which may change in response to higher temperatures and human activity – will also affect changes to the water cycle. The effects of glacier and snow cover shrinkage in mountain environments reflect complex interactions between water resource systems and glacial meltwater. Demand for water and future water security will be determined by a range of influences, both related to climate change (e.g. for irrigation) and not (e.g. population growth and urbanisation).

While there is very high confidence that climate change is ongoing and set to continue, there is less certainty around how exactly key elements of the water cycle will evolve. Uncertainty is particularly high in relation to future precipitation patterns, due largely to differences between climate model results and exacerbated by the fact that precipitation may fluctuate over the course of decades, inducing wet and dry periods in the same location over time. Overall, however, there will be a higher frequency and intensity of floods. It is also expected that precipitation globally will increase because warmer temperatures increase evaporation and allow the atmosphere to hold greater volumes of water vapour.

Recent events are highlighting the vulnerability of water supply systems to prolonged drying, for example the ‘Millennium drought’ in Australia, and drought conditions in California. Cape Town’s high profile ‘Day Zero’ brought the city close to a major water supply crisis as reservoirs were almost depleted. While drought was not the only cause, the Cape Town case exemplifies the kind of threat that climate change represents for water security.

The implications of climate change for water security range from large-scale shifts in the flows of transboundary river systems (that cross multiple territories) to disruptions to local unimproved water sources (which include unprotected wells, springs and surface water). Changing patterns of extremes will also increase flood risk with consequences for individual and community wellbeing through physical impacts and the psychological effects of risk exposure and trauma recovery.

Wide-ranging secondary effects of climate change on food and energy production and land use are likely to cause even further disruption to water management systems.

How are water resources managed?

Management of water resources underpins urban water supply, provision of agricultural irrigation (which is globally by far the largest consumer of water) and industrial processes such as the cooling of power plants. Traditionally, management has relied on the assumption that our climate and water sources are stable (or ‘stationary’) over the long term, but climate change undermines this assumption.

While water management systems already have strategies to deal with a certain level of variability and uncertainty (e.g. water storage, water demand management and early warning systems), it is questionable whether these will be sufficient to cope with the projected rate and magnitude of change to water resources under climate change.

Investments in large-scale water infrastructure are still often made under the assumption that rainfall or streamflow patterns will resemble historical patterns (i.e. they are stationary over the long term). But with their long operational lifetimes they will be exposed to a much wider range of variability and extremes than currently experienced. This poses severe risks to performance and while guidelines for incorporating climate resilience into large-scale water projects are emerging, these are optional and rarely adopted.

What adaptation is needed?

Uncertainty about how the climate will evolve continues to have an important bearing on practical approaches to adaptation in the water sector. Currently, climate models lack the spatial and temporal detail often required for adaptation planning. This means that adaptation should factor greater levels of uncertainty into water resource planning and consider how water systems can cope with a wide range of future climate conditions, alongside other factors such as increasing urbanisation, development and population growth.

Water resource planners and managers are learning to address these new challenges while practitioners are grappling with changing risk profiles and their operational implications. Adaptation requires technical and engineering strategies (e.g. water storage, water saving devices, flood protection measures) to secure safe water supply as well as socioeconomic responses to maintain a sustainable level of demand and equitable accessibility. Early warning systems for flood or drought events may integrate physical (improved forecasts) and social elements (improved risk communication). Involving communities and stakeholders at all points in these processes can guide effective and robust adaptation pathways that are tailored to local contexts.

Factoring climate change into planning is already becoming a requirement in some jurisdictions. For example, the UK’s Climate Change Act requires Water Resource Management Plans which are to be published every five years covering a minimum period of 25 years. Adaptation options proposed for the UK include achieving formal international standards of resilience, strengthening building regulations, water metering and enhanced drought management.

While there are many adaptation strategies to strengthen resilience and water security, challenges include unequal access to certain options and a lack of detailed evidence on their effectiveness, particularly at higher levels of global warming.

This Explainer was written by Declan Conway.