Water and climate: The gathering storm

There is enough scientific evidence to show that the increasing variability in the hydrological cycle witnessed over the last 30 years in many parts of the world is not just a blip on the meteorological time chart. It is with us to stay and the chances are it is going to intensify further as global warming adds to the climatic turbulence. Perversely too it is the developing countries of the South that are most vulnerable to the effects of climate extremes. The growing number of weather-related disasters puts ever-increasing demands on humanitarian relief and is already threatening governments’ poverty alleviation and sustainable development targets.

There is another ominous effect that compounds the impact of regular disasters. Water resource planners seek to match the forecast demands of future populations for water, food, power and industrial development with the supplies that can be made available on a sustainable basis from rivers, lakes, reservoirs and aquifers. Historically, a largely predictable hydrological cycle has meant that reservoir storage volumes and operating rules could be used to balance the effect of wet and dry seasons. Using past records of rainfall and river flows and allowing for evaporation and other losses, water engineeers and hydrologists could confidently design water management systems that would deliver dependable supplies throughout the year and regulate rivers to moderate the effects of seasonal fluctuations. Now those fluctuations have gone off the charts.

Sometimes, as in the Sahel region of Africa, it is a progressive fall in annual rainfall and average river flows that reduces the overall water availability. In other cases, like El Salvador, annual precipitation does not change, but the rain comes in brief intense storms interspersed with prolonged dry periods. The result is floods and droughts that overwhelm the capacity of the infrastructure to cope. What this means is that the hydro-meteorological design parameters may no longer be valid. Factoring in the intensified hydrological cycle and the predicted effects of climate change, for regions that already suffer from water shortage, will often mean that the average water yields are reduced, requiring storage capacity to be increased. Not always though: in the three most waterscarce regions of China, the yield from current storage facilities actually increases between now and 2050 for each of the development scenarios commonly used to model climate change.

So, water policy makers face a double challenge: more disasters mean increasing recovery costs; and, for some
regions, reduced yields make it even harder to meet the rising demands for water. The purpose of this document is to point to potential solutions.

In its report, Climate changes the water rules, the Dialogue on Water and Climate has put together a wealth of evidence on climate variability and climate change. With the help of 18 multi-stakeholder Dialogues across the globe, and inputs from thematic experts on water resources management and wider development issues, DWC has assembled a "Compendium" of coping options – a menu of actions that can help communities, governments and support agencies to adapt to today’s and tomorrow’s turbulent climate.

Click here to view a bullet-point summary of the reasons why we need to act now.