Water-Related Climate Risks
Content Table
Future changes in the hydrological cycle may have important impacts on the society, e.g. with regard to flood risks, water availability and water quality. Although climate observations do not show consistent global trends in the hydrological cycle despite of the global warming in the past century, strong regional and seasonal changes are possible. Even if for some regions the mean hydrological cycle may not change, a change in the intensity distribution of precipitation may have significant impacts (Lorenz et al. 2008).
Changing water levels, temperatures and flow will in turn affect food supply, health, industry, transportation, and ecosystem integrity.
Climate change and the water cycle
In their third assessment report, the Intergovernmental Panel on Climate Change (IPCC) concludes that the Earth’s surface is warming, average precipitation patterns are changing and global sea level rises.
Spatial variability in the hydrological cycle and its development are large, leading to large differences between the regions, as compared to a global average. There is still relatively high uncertainty in prediction of regional climate development. Across most climate change scenarios, an increase in annual mean precipitation in high latitudes and Southeast Asia, and decreases in central Asia, the area around the Mediterranean, southern Africa and Australia is projected (IPCC, 2001).
However, climate change will not only induce a gradual change in annual means. Climate change (natural and man-made) has a significant impact on the hydrological cycle. Higher greenhouse gases concentration in the atmosphere causes changes in the energy balance on the Earth surface, resulting in a higher atmospheric temperature, and thus, according to the basics of thermodynamics, an ‘intensification’ of the hydrological cycle.
As a consequence, it is expected that climate extremes will increase substantially. Small changes in climate may have a large impact on the probability distribution of extreme weather events (floods, drought, storms) in space and time, and on the intensity of extremes (IPCC, 2001).
Recently, a number of groups and institutions analysed the occurrence of hydro-meteorological disasters and the corresponding human and economic costs posed on societies (e.g. World Bank, 2005; UNDP, 2004; IFRC, 2001). A trend in the increasing number of disasters can already be documented (see Figure 1).
Figure 1: Number of disasters reported (source: IFRC, 2001)
Key changes to the hydrological cycle (associated with an increased concentration of greenhouse gases in the atmosphere and the resulting changes in climate) include:
- Changes in the seasonal distribution and amount of precipitation.
- An increase in precipitation intensity under most situations.
- Changes in the balance between snow and rain.
- Increased evapotranspiration and a reduction in soil moisture.
- Changes in vegetation cover resulting from changes in temperature and precipitation.
- Consequent changes in management of land resources.
- Accelerated melting glacial ice.
- Increases in fire risk in many areas.
- Increased coastal inundation and wetland loss from sea level rise.
- Effects of CO2 on plant physiology, leading to reduced transpiration and increased water use efficiency (Goudie 2006).
Droughts
The term drought may refer to a meteorological drought (precipitation well below average), hydrological drought (low river flows and low water levels in rivers, lakes and
groundwater), agricultural drought (low soil moisture), and environmental drought (a combination of the above). The socio-economic impacts of droughts may arise from the interaction between natural conditions and human factors such as changes in land use, land cover, and the demand for and use of water. Excessive water withdrawals can exacerbate the impact of drought.
In regions that are already suffering from drought, climate change is expected to have an exacerbating effect: it may cause a decrease in precipitation combined with an increase in evapotranspiration. Climate change would make marginal areas into drought areas. Increases in agricultural intensity and population density on top of climate change contribute further to drought situations. The consequences of hydrological droughts depend on regional / local circumstances (soil type, crop type, availability and depth of groundwater, water storage etc.).
Droughts affect rain-fed agricultural production as well as water supply for domestic, industrial and agricultural purposes. Some semi-arid and sub-humid regions, e.g., Australia, western USA and southern Canada, and the Sahel, have suffered from more intense and multi-annual droughts.
Floods
Sea level rise at the moment is about 10-20 cm per century, but the climate change will increase the speed of absolute SLR due to thermal expansion of water at higher temperatures and the melting of glaciers and land ice. Recent global estimates show a rise of several to a number of decimetres above the 1900-level at present and up to a metre in the coming century on top of the ongoing land subsidence in certain areas. However, there are large differences between regions in relative sea level rise.
Several factors contribute to the increase of river floods. In almost all mountainous regions, glacier retreat is causing a decrease in snow melt, leading to a lower base flow in rivers. With higher temperatures winter snow melts quicker, leading to an increase in peak flows. Furthermore, almost all models predict more dynamics in rainfall patterns leading to even more pronounced peak flows in rivers. Regional climate change projections differ substantially with respect to peak rain fall, snow and glacier developments. In combination with climate drivers, changing land use will still remain to be on of the main culprits behind increased flood risks in the future.
Tropical Storms
The influence of global warming on the occurrence and magnitude of tropical storms is subject to an ongoing scientific discussion. Many climate models (but not all) also predict an increase in the magnitude of tropical storms. Furthermore, with increasing sea water temperatures, the geographical area in which cyclones can develop could extend, resulting in larger coastal zones under risk.
-------------------------------------------------
Examples of possible impacts of climate change due to changes in extreme precipitation-related weather and climate events, based on projections to the mid- to late 21st century. These do not take into account any changes or developments in adaptive capacity (IPCC 2008):
Related Articles
Article 1
Article 2
Article 3
References
Biemans, H. et al. 2006. Water and Climate Risks: A Plea for Climate Proofing of Water Development Strategies and Measures. Co-operative Programme on Water and Climate. The Netherlands
IFRC, 2001. World Disasters Report 2001. International Federation of Red Cross and Red Crescent Societies. Geneva, Switzerland
IPCC, 2008. Climate Change and Water. IPCC Technical Paper VI.
Lorenz, S.J. et al. 2008. Global Water Cycle and Climate Change. In Lozán et al. "Global Change: Enoguh Water for All?", Wissenschaftliche Auswertungen, Hamburg
UNDP, 2004. Reducing Disaster Risk: A Challenge for Development. A global report.
UNDP, 2004. Reducing Disaster Risk: A Challenge for Development. A global report.
World Bank, 2005. Natural Disaster Hotspots: A global risk analysis. World Bank. Washington, D.C.
http://www.climate.org/topics/water.html
Links
Link 1
Link 2
Link 3
