5 Changing climate
The climate is believed to be changing as a result of increased emissions of some gases to the atmosphere by human activities, especially by our use of fossil fuels. The UK Climate Impacts Programme (UKCIP) has identified that mean annual temperatures in the UK have increased by about 0.7 °C over the last 300 years, with most of this, about 0.5 °C of warming, occurring during the 20th century. This warming is predicted to continue throughout the 21st century.
Detailed prediction of climatic change is difficult, because of the natural variability of the climate, which may magnify or reduce the effect of climate change on a shorter timescale. Some events that we have been experiencing recently (droughts and floods) may be part of the natural variability, or extremes caused by the changing climate.
Planning for future water resources in the UK has to take into account climatic changes. Current (2004) climatic change predictions by UKCIP suggest that:
- the average annual temperature across the UK will rise by between 2 °C and 3.5 °C by 2080;
- the warming will be greater in the south and east of the UK;
- winters will become wetter and summers will become drier, though even by the 2020s, changes will still be within the range of the natural variations we experience now;
- the annual variability of rainfall will increase — there will be both more wet years and more dry years.
Climate change affects planning for water resources in three ways.
- Demand for water Domestic water use is likely to increase due to hotter summers, mainly due to increased washing and garden watering. The total impact on industrial water use is uncertain; some uses will increase (e.g. water cooling is less efficient at higher temperatures so the demand may increase) and some will decrease. Agricultural water demand will increase (e.g. for greater irrigation and more drinking water for livestock).
- Availability of water Higher winter rainfall will increase river discharge, reservoir replenishment and aquifer recharge in winter, but summer discharges and infiltration will decrease, particularly in the south and east. Water availability will therefore become less reliable. Evaporation will increase due to higher temperatures.
- Environmental impact Changes in river discharge and groundwater levels will have an impact on the plants and animals that rely on the water environment; some will thrive under the changed conditions and some will find it hard to survive. Designated conservation areas will need protection by reducing abstractions to maintain summer flows and groundwater levels (Figure 9).