6C - Uncertainty
Climate change resulting from short term oscillations (ENSO cycles) and global warming increase the uncertainty in the system; this causes concerns over the future of water supplies. (F: Projections of future drought and flood risk)
One of the problems with this forecasting of possible changes to the hydrological cycle is distinguishing between the impacts of long-term climate change and those of the short-term oscillations associated with El Niño events. A further complication results from the fact that ENSO cycles are associated both with extreme flooding in some parts of the world, and extreme drought in others.
What is perhaps of more concern is the potential impact of short-term climate change (regardless of whether or not it is related to ENSO cycles) on global water supplies.
Factors leading to diminishing water supply and increased uncertainty
- Increases in annual temperature lead to greater evaporation from surface water and reservoirs in summer, although spring discharge may increase
- Greater rates of evapotranspiration, desiccation of forest stores
- Impact of oscillations, e.g. ENSO, is leading to increasingly unreliable patterns of rainfall, e.g. less predictable monsoons
- More frequent cyclone and monsoon events threaten water supplies intermittently
- Increased intensity and frequency of droughts as a result of global warming and oscillation is issue for rainfed agriculturalists
- Depleted aquifers lead to problems with groundwater
- Decreasing rainfall in many areas as a result of global warming
- Loss of snow and glaciers as a store threatens many communities in mountain ares, e.g. Himalayas
Uncertainty arises because modern scientific research is unable to make confident forecasts about the future availability of water. But even if scientists were able to do this, there are other important unknowns to be taken into account, such as possible advances in water technology and factors related to the demand side, such as population growth and the rising tide of global development.