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Climate change and water: Understanding impacts, formulating responses

Time (GMT +01) 11:00 12:15


Prof Nigel Arnell - Director, Walker Institute for Climate Systems Research, University of Reading

Margaret Catley-Carlsson - WEF Global Agenda Council on water


Roger Calow - Programme Leader, Water Policy Programme, ODI

Professor Nigel Arnell explained that his presentation would cover four areas:

  • The consequences of climate change for water in the absence of any action
  • The effects of mitigation
  • Adaptation and uncertainty
  • New scientific developments to address uncertainty

He presented three key conclusions from the 2008 IPCC Technical Report on Climate Change and Water:

  • Changes in water quantity and quality due to climate change are expected to affect food availability, stability, access and utilisation
  • Climate change affects the function and operation of existing water infrastructure as well as water management practices: climate change demands not just “more of the same with an extra safety gap”
  • Several gaps in knowledge exist in terms of observations and research needs, in particular: there is little on practical experiences of coping with climate variability and change, and little information from developing countries

Arnell then showed a map of projected future hydrological changes. Higher latitudes are expected to become wetter, the dry subtropics drier, and the humid tropics wetter under most projections. However he pointed out some areas of great uncertainty, including the impacts on the South Asian monsoon. He then discussed some more detailed hydrological consequences of climate change:

  • Changes in timing of streamflow throughout the year
  • Changes in the frequency of extreme events such as droughts
  • The hydrological impact of glacier melting – this is not well understood
  • Potential for deterioration of water quality with increasing temperatures

Arnell explained that the link between hydrological change and the impact on water resources is complex, and depends on the characteristics of the water management system. Further, climate change is not the only driver of change in hydrological regimes. Other effects may mask or compound the climate change impact.

He then presented the effect of mitigation policies. Even with a strong mitigation policy a temperature increase of 1.2 degrees is expected, and mitigation is expected to have relatively little impact on the number of people to be affected by increased water stress.

Arnell then noted that projected hydrological effects and water resource impacts depend on which climate change projection is used. In some areas these do not agree well.

He then discussed the implications of this uncertainty for adaptation, making three key points:

  • We cannot assume the past is a good guide to the future.
  • We cannot make forecasts of the future.
  • The most credible approach is to use scenarios to describe feasible possible futures.

He explained that there are two ways to cope with these multiple scenarios:

  • A “risk-based” approach based on an evaluation of the relative likelihood of different outcomes
  • A “robustness” approach based on exploring the sensitivity of decisions to alternative scenarios.

He noted that the risk-based option is very difficult to implement and suffers some conceptual challenges. Seeking robust, flexible adaptation approaches is a better way forward.

Finally Arnell discussed two new scientific developments which may help to address the problem of uncertainty.

  1. New high-resolution climate models, which build up climate from an understanding of weather systems, are beginning to provide credible projections of likely changes in extreme events. This is very significant because most water systems are influenced more by extreme events than by average conditions, but current models are not good at projecting this variability.
  2. Forecasting techniques, focusing on some aspects of climate which seem to be predictable based on patterns of oceanic change, are beginning to provide insight into likely changes in climate over the next few decades – i.e. over adaptation timescales. This is extremely useful as till now it has been difficult to interpolate between current conditions and scenarios for 50 or 100 years in the future.

Margaret Catley-Carlson started with some facts including:

  • Freshwater is only 2.5% of the earth’s water, and of that only 1-2% is usable.
  • People require 2 litres per day for drinking, 25 for cooking and sanitation, but 2500 for food.
  • 6000 children die every day due to a lack of clean water and sanitation.
  • 90% of urban wastewater in least developed countries is untreated.
  • The poor spend more on water than the rich, and free water hurts the poor most.
  • Water tables are declining around the world, and many rivers are closing.
  • Many freshwater species are in peril and deltas and wetlands are disappearing.

She attributed the decline in the water resource to “three Ps”: Population, Prosperity (which increases demand for water and in particular meat), and Pollution.

She said that food demand is likely to double over the next 50 years due to population increase and changing diets – particularly with increased meat production. Water needs will double unless we can make productivity gains.

She highlighted that climate change will probably exacerbate existing challenges. Effects will also combine, for example higher temperatures will mean more evaporation from soil and plants, meaning less water will flow into rivers and aquifers from the soil

She then explained that her talk would discuss the implications of declining water resources for security, disasters, infrastructure, agriculture and food security, and sought to identify some escape routes.

On security, she showed that a global map of recent conflict sites and showed the overlaps with water stress hotspots. She also noted that many of these locations are also expected to experience increased water stress under climate change. However she said that most shared basins had so far avoided conflicts over water.

She then discussed disasters, showing that the occurrence of windstorms and floods has increased significantly since 1980, and much more than geophysical events, indicating the influence of climate change.

On infrastructure, she highlighted that investments made today in water-related infrastructure would have to be designed for the future as well as the present. She said that businesses often have an interest in water resources and are taking this on board– those who have not have suffered. Water is being discussed at fora such as the Business Council on Sustainable Development and World Economic Forum.

On food security, she stated that climate change could mean agricultural losses equivalent to the entire grain crops of the US and India combined. She presented a map showing that in several critical grain-producing areas (parts of India, the US, China and Europe), water withdrawals are already exceeding the natural supply.

Catley-Carlson then discussed ways forward. She emphasised the need for “soft” solutions such as protecting forests and wetlands, addressing industrial pollution, and integrated water resource management, and noted that some countries have taken steps forward. Saudi Arabia, for example, has abandoned major wheat irrigation programmes in the desert. It is now buying tracts of land elsewhere to grow food on, a trend she suggested was likely to increase. She also presented graphs showing the huge yield increases that have been achieved since the 1940s, and emphasised that efforts have to be made to increase yields in sub-Saharan Africa in particular, by both investing in expanded irrigation and upgrading rain fed agriculture. The productivity attained from livestock water can be also be increased by changing to new breeds.

Finally, she noted that the changes needed are principally not scientific or technical advances, but changes in the institutional and political systems managing water. Politicians who attempt to charge more for water tend not to be elected. She concluded that the real problem is the question of for whose benefit policy is made – the answer is seldom the poor. Yet we have no choice but to manage water better.

Questions from the floor followed the presentations. These included the following:

  • Are the models used by the IPCC, which do not incorporate newly recognised feedback systems such as Arctic methane, too far out of date? Arnell responded that while models are continually improved and made more robust, we should not wait until they are perfect to start using them. He also explained that the models currently being used do include most of what is going to cause change.
  • Is there a role for a water footprint similar to the carbon footprint concept? Catley-Carlson replied that footprints are useful in policy terms because they are easy to understand, but their simplicity is also a problem. The water footprint of any item depends on where it is made, and local context also determines whether production is a valuable source of income or an unsustainable drain on resources.
  • What do the white areas on the maps of projected changes in run-off indicate? Arnell replied that these are areas where the different projections (which are averaged to produce the map) do not agree on a direction of change so there is no best estimate of how runoff will change.
  • How accurate are alarmist articles predicting conflict over water? Catley-Carlson cited Aaron Woolf’s work in response, which has shown that cooperation usually outdoes conflict in shared basis. His thesis is that where countries have a reasonable relationship and strong institutions for other relations such as trade, they are likely to cooperate over water. Where the opposite is true, however, sharing water could catalyse conflict. She gave the example of the US-Canada International Joint Commission which has successfully mediated water sharing.
  • Is population the most certain and largest short-term impact on water resources? Catley-Carlson responded that population is a major driver, and that climate change will probably cause huge migrations out of difficult areas. But she noted that population is a sensitive issue that is not widely discussed.
  • How can subsistence farmers be encouraged to take on higher risk strategies to increase their production? Catley-Carlson replied that many subsistence farmers have shown an amazing ability to adapt, but that there will be limits to adaptation and ultimately many will need to move off the land to increase their incomes.
  • Why does free water hurt the poor most? Catley-Carlson explained that water supply systems in many places are in disrepair and have not been extended to poor areas because they are severely underfunded, leaving the poor dependent on more expensive private water provision from vendors and similar. Where there are fair tariffs for water, poor people pay less and there is money to invest in network expansion to cover everyone – e.g. Kigali and Entebbe.
  • Given the decline in water resources, why has a decreasing share of ODA been allocated to water over the last ten years? Catley-Carlson replied that ODA has to be responsive to the priorities of receiving governments, and water (and particularly sanitation) are often not high on their agendas. There is a lack of effective demand for financing in water. She also observed that more could be done to raise local financing such as from pension funds.
  • Nicholas Stern said that adaptation was “development in a hostile climate” – yet Arnell stated that we cannot just do “more of the same” – what is the answer? Arnell replied that adaptation must take place in the context of development. The extra dimension in adaptation is not the techniques used but the degree of uncertainty, demanding new criteria of robustness and flexibility not just dollar returns based on fixed estimates. Catley-Carlson observed that this will be difficult for the lending and granting communities to handle.


The importance of freshwater to our life support system is now widely recognised, as are the consequences of water insecurity and water resources degradation. There are many pressures on water – population growth, urbanisation, land use change and the need to grow more food, to name but a few. Climate change is an added pressure, but how much do we know about its impacts on water systems and livelihoods, which areas and populations are most vulnerable, and what can we do to ensure that human and environmental needs are protected? 

In this, the eigth meeting in the ‘Climate Change and International Development’ Series, Professor Nigel Arnell and Dr Margaret Catley-Carlson discussed the scientific evidence linking climate change and water in developing countries, and the threats and opportunities arising from existing and future climate variability. So far, these issues have not been adequately addressed in either climate change analyses or policy debates in the water sector, as the recent IPCC Technical Paper on Climate Change and Water recognises. This meeting was therefore a timely and important contribution to a much needed discussion.