Climate Change and Water Supply - Consequences of Climate Change and Potential Adaptation Strategies - page 02

 

Quantitative and qualitative aspects of changed water availability

While precipitation and total runoffs that increase on a multi-year average may definitely improve the water supply situation in some regions, the water industry will nevertheless have to adapt to a seasonally or intermittently diminished availability of water. Whether or not a permanent or temporary reduction in water availability will lead to a critical situation for a water supply system depends on a multitude of local factors, such as the following:

  • the existence or non-existence of alternative water sources and sufficiently flexible local water abstraction facilities enabling utilities to respond to a (temporary) loss of individual abstraction types/catchment areas;
  • the existence of competing water uses and their increasing significance, if applicable (especially agricultural irrigation); and
  • the expected development of water use.

The following consequences of changes in water resources availability loom ahead:

Groundwater

A permanently declining and seasonally diminished or absent groundwater recharge entails a concurrent sinking of the water table. The water resources availability situation will deteriorate particularly where (seasonally) diminished groundwater recharge affects comparatively small groundwater systems which are less capable to buffer precipitation variabilities. Springs fed by small or near-surface aquifers are especially sensitive to changes of water resources availability.

By contrast, in regions where groundwater recharge takes place almost exclusively during winters, and where winters are getting wetter, average groundwater levels are expected to rise. This may cause water logging and damage to buildings, especially when increasing recharge is accompanied by a lower water demand.

Changes in water resources availability may also result in major groundwater quality changes, e.g. a non-dilution of contaminated groundwater may lead to higher pollutant concentrations in the raw water.

Lower back pressures caused by sinking groundwater levels will lead to deep-well pump cavitation problems and may cause wells to run dry in extreme cases.
In coastal regions, the expected sea level rise may result in salt water intrusion into coastal aquifers.

A permanently improved water resources availability is expected for regions with increasing groundwater recharges and larger groundwater resources.


 

Lakes and reservoirs

Seasonally and intermittently sinking levels of lakes and reservoirs will generally diminish raw water availability exactly during peak demands.

This may result in smaller depths of the storage volumes suitable for raw water withdrawal, a smaller portion of cold deep water (hypolimnion) and in decreasing back pressures at withdrawal points. Beyond this, the capacities to buffer polluted inflows and water withdrawal control options may be compromised.

Rain storms may adversely affect raw water quality as they may cause erosive runoffs and an increase in spillovers from separate and combined sewerage systems entailing increased inputs of sediment and particle-bound contaminants and microorganisms.

Climatic changes will more severely affect the quality of small and shallow waters and waters with a higher trophic level than that of deep and oligotrophic waters.

Watercourses

The risk of flooding increases with the rising frequency of rain storms. Floods may adversely affect groundwater quality and mobilise dangerous substances e.g. from industrial brownfields. Extremely high water levels may submerge bank filtration systems and thus directly pollute raw water.

During extremely low flows water withdrawals from rivers might need to be reduced or even ceased.

Lower river flows may lead to higher concentration of pollutants and adversely affect raw water quality. This is relevant also when river water is used for artificial groundwater recharge or bank filtration. The Polluter Pays Principle (PPP) is particularly significant against this backdrop.

Rain storms may adversely affect raw water quality as they may cause erosive runoffs and an increase in spillovers from separate and combined sewerage systems, entailing increased inputs of sediment- and particle-bound contaminants and microorganisms.

Rain storms, floods and persisting periods of drought may interfere with utility operation and, in some exceptional cases, result in a temporary water supply cut-off.