Réf. Goudie 2006 - A

Référence bibliographique complète
GOUDIE, S.A. Global warming and fluvial geomorphology. Geomorphology, 2006, 79, 384-394.

Abstract: Future global warming has a number of implications for fluvial geomorphology because of changes in such phenomena as rates of evapotranspiration, precipitation characteristics, plant distributions, plant stomatal closure, sea levels, glacier and permafrost melting, and human responses. Potential changes in rivers are outlined in this review in the context of changes in the intensity of rainfall, the activity of tropical cyclones, runoff response (including that of Europe, dry lands and high latitude environments), and geomorphological reactions, including rates of soil erosion. In general, however, much work remains to be done to establish the full range of geomorphological responses that may take place in fluvial systems.

Mots-clés
Global warming, fluvial geomorphology, runoff, snow pack, deltas

Organismes / Contacts
St. Cross College and Oxford University Centre for the Environment, St Cross College, Oxford, OX1 3LZ, Oxford, UK

(1) - Paramètre(s) atmosphérique(s) modifié(s)
(2) - Elément(s) du milieu impacté(s)
(3) - Type(s) d'aléa impacté(s)
(3) - Sous-type(s) d'aléa
Temperature, rainfall intensity Snow cover, permafrost Floods  

Pays / Zone
Massif / Secteur
Site(s) d'étude
Exposition
Altitude
Période(s) d'observation
World (USA, China, Europe...) Rhine watershed        

(1) - Modifications des paramètres atmosphériques
Reconstitutions
 
Observations
During recent warm decades, some evidence exists that rainfall events in a number of countries have become more intense. Examples are known from the United States, Canada, Australia, Japan, South Africa [see references in the study], and Europe (Forland et al., 1998).
Modélisations
 
Hypothèses

Some key changes in the [climatic and] hydrological system associated with elevated levels of the atmospheric greenhouse: Changes in precipitation amount and seasonal distribution, possibly increased intensity of precipitation, change in balance between snow and rain, increased evapotranspiration and loss of soil moisture.


Informations complémentaires (données utilisées, méthode, scénarios, etc.)
Use of General Circulation Models by various authors for predicting global warming impact on precipitation.

(2) - Effets du changement climatique sur le milieu naturel
Reconstitutions
 
Observations
 
Modélisations
Arnell (1999) has modeled potential changes in hydrological regimes for mainland Europe, using four different GCM-based climate scenarios. While differences exist between the four scenarios, each indicates a general reduction in annual runoff in Europe south of around 50°N and an increase polewards of that. The decreases could be as great as 50% and the increases up to 25%.

The proposed decrease in annual runoff in southern Europe is also confirmed by Menzell and Burger's (2002) work in Germany, for they also suggest that peak flows will be very substantially reduced. A model by Eckhardt and Ulbrich (2003) for the Rhenish Massif in Germany found that in summer mean monthly groundwater recharge and stream flow may be reduced by up to 50%.

One of the most important rivers in Europe, the Rhine, stretches from the Swiss Alps to the Dutchcoast and has a catchment covering 185,000 km2. Models suggest that its discharge will become markedly more seasonal by the end of the century, with mean discharge decreases of about 30% in summer. The decrease in the summer discharge is related mainly to a predicted decrease in precipitation combined with increases in evapotranspiration. Increases in winter discharge will be caused by a combination of increased precipitation, reduced snow storage and increased early melt. Glacier melting in the Alps also contributes to the flow of the Rhine. Once these glaciers begin to disappear, this contribution will diminish sharply, and will eventually cease.
Hypothèses

Following a global analysis of future hydrological trends, Nijsssen et al. (2001) suggested that the largest changes in the hydrological cycle are predicted for the snow-dominated basins of mid to higher latitudes, and in particular marked changes are likely in the amplitude and phase of the annual water cycle (Arora and Boer, 2001). Some of the main tendencies in runoff that are likely to occur in Europe are: Increased winter precipitation and decreased summer precipitation, general intensification of precipitation, increased moisture loss through increased evapotranspiration, less winter snow pack, earlier melting of snow pack,smaller glacial contribution to summer flow.

Vegetation cover will respond to temperature and precipitation changes and to fire frequency, with concomitant changes in sediment yields and the operation of erosional processes. Higher atmospheric CO2 levels may stimulate plant growth and leadto changes in the efficiency of water use by plants and, thus, to transpiration and runoff (Eckhardt and Ulbrich, 2003).

Changes will occur in the amount, intensity, duration, type and timing of precipitation, which will affect river flows and groundwater recharge. On a global basis it is possible that runoff will increase in a warmer world because of a global increase in precipitation (Douville et al. 2002) and historical discharge records indicate that global runoff increases by ca. 4% for each 1 °C rise in temperature (Labat et al., 2004). Major regional differences, however, will occur.

Rising temperatures will affect snowfall and snowmelt (Seidel et al. 1998). Under relatively mild conditions, even a modest temperature rise might mean that snow becomes virtually unknown, being replaced by rain, so that the spring peak attributed to snowmelt would be eliminated. It would be replaced by higher flows during the winter. Under more extreme climatic conditions, all winter precipitation would still fall as snow, even with a rise in temperature. As a consequence, the snowmelt peak would still occur, although it might occur earlier in the year.


Sensibilité du milieu à des paramètres climatiques
Informations complémentaires (données utilisées, méthode, scénarios, etc.)
   

(3) - Effets du changement climatique sur l'aléa
Reconstitutions

 

Observations
 
Modélisations
 
Hypothèses
As slopes over steepened by previous glacial erosion are deprived of the buttressing effects of glaciers, they can become unstable and generate a risk of increased landsliding and debris avalanches (Kirkbride and Warren, 1999; Holm et al., 2004). Haerberli and Burn (2002) have shown the association between glacier retreat, since the Little Ice Age, and processes of slope movements, such as gravitational deformations of rock slope, rock avalanches, debris flows, and debris slides.

In mainland Europe, vulnerability to flooding seems to be increasing because of such factors as the occupation of floodplains by more people and the engineering structures, and unusually severe floods affected much of the continent during the 1990s and early 2000s (Mitchell, 2003). Therefore, a major question is the extent to which future flooding may be exacerbated by climate change.

Paramètres de l'aléa
Sensibilité du paramètre de l'aléa à des paramètres climatiques et du milieu / Facteurs de contrôle
Informations complémentaires (données utilisées, méthode, scénarios, etc.)
     

(4) - Remarques générales

 


(5) - Syntèses et préconisations

River systems will respond to global warming in some very significant ways, notably in cold, tropical and arid regions, but also more generally. Some areas will experience overall increases in runoff, while others will experience decreases. More intense rainfall may cause more widespread flooding in some catchments. The annual flow regimes will be modified by changes in such phenomena as snow packs. While bedrock and armored channels may be robust, alluvial channels may be substantially more sensitive to discharge changes, as the history of the arroyos of the American Southwest has so clearly shown. Rates of erosion and sediment yields will also change in response to precipitation changes, fire frequencies and land cover changes. Modeling studies from a range of different environments suggest that the increases in rates of erosion could be on the order of 25–50%. Coastal deltas will respond to the combined effects ofs ea level rise, local subsidence, and the speed of sediment accretion.

Therefore, while geomorphologists, following the lead of George Perkins Marsh, have historically tended to examine the effects of a range of anthropogenic processes on river systems, such as land use change, dam construction, water abstraction and inter-basin water transfers, we are nowenteringanera when such processes, while continuing to operate, will be joined by the many changes that will be caused by climate warming. Geomorphologists have yet to devote to this theme the same amount of attention that has been expended by, for example, life scientists and hydrologists. Remarkably few scenarios for future geomorphological changes have been developed. This is a major research priority.

Références citées:

Arnell, N.W., 1999. The impacts of climate change on water resources. Meteorological Office, Climate change and its impacts. Hadley Centre, Bracknell, pp. 14–18.

Arora, V.K., Boer, G.J., 2001. Effects of simulated climate change on the hydrology of major river basins. Journal of Geophysical Research 106 (D4), 3335–3348.
 
Douville, H., Chauvin, F., Planton, S., Royer, J.-F., Salas-Mélia, D., Tyteca, S., 2002. Sensitivity of the hydrological cycle to increasing amounts of greenhouse gases and aerosols. Climate Dynamics 20, 45–68.

Eckhardt, K., Ulbrich, U., 2003. Potential impacts of climate change on groundwater recharge and streamflow in a central European low mountain range. Journal of Hydrology 284, 244–252.

Haerberli, W., Burn, C.R., 2002. Natural hazards in forests: glacier and permafrost effects as related to climate change. In: Sidle, R.C. (Ed.), Environmental change and geomorphic effects in forests. CABI, Wallingford, pp. 167–202.
 
Holm, K., Bovis, M., Jacob, M., 2004. The landslide response of alpine basins to post-Little Ice Age glacial thinning and retreat in southwestern British Columbia. Geomorphology 57, 201–216.

Kirkbride, M.P., Warren, C.R., 1999. Tasman Glacier, New Zealand: 20th century thinning and predicted calving retreat. Global and Planetary Change 22, 11–28.
 
Menzell, L., Burger, G., 2002. Climate change scenarios and runoff response in the Mulde catchment (Southern Elbe, Germany). Journal of Hydrology 267, 53–64.

Mitchell, J.K., 2003. European river floods in a changing world. Risk Analysis 23, 567–574.

Nijssen, B., O'Donnell, G.M., Hamlet, A.F., Lettenmaier, D.P., 2001. Hydrologic sensitivityof globalrivers to climate change. Climatic Change 50, 143–175.