Programme OS3g Climate change: disasters
and extreme events
Impact of climate change on hydrological risks
Author(s): Philippe Cantet,
CEMAGREF, 3275 route de Cézanne CS 40061,
Provence, Cedex 5.
Keyword(s): climatic changes, hourly rainfall generation model, rainfall-flow model, hydrologic
Session: OS3g Climate change: disasters
and extreme events
Nowadays, climate changes are widely considered a reality by scientists (IPCC,
2001). Since the preindustrial period, observations have shown a significant evolution of mean annual pluviometry
(higher or lower depending on the geographical area). Nevertheless, scientists cannot easily evaluate its impact on
the extreme hydrometeorologic phenomena using classical statistical techniques. This problem comes from a lack of
distancing in the observed rain event time series to evaluate the tendency of extreme phenomena. Besides, global
climatic models show many difficulties in modelling extreme meteorological processes. Only studying the flow is not
sufficient because of changes in basin, independently of climate change (urbanisation, fire, deforestation, hydraulic
installations…). An original approach to study climate change is proposed by modelling flood generator processes
using an hourly rainfall generation model adapted to different climates  coupled with rainfall-runoff modelisation
The main objective of the research is to evaluate, by rainfall-runoff modelisations, which impacts climate
changes might have on floods. For example, evolution of climatic boundaries, which are important in the translation in
hydrologic risks, will be studied.
To show the detection of climate changes, parameters of the rainfall stochastic
generator are evaluated from many ranges of time and calculated by different statistical tests. In contrast to classical
methods, the model parameters are calculated by mean climatic characteristics and not by extreme values. So the
three parameters: occurrences of events, duration of events, and the intensity of rainfall, which are particularly well
adapted to examine rain signals, are not sensitive to the sample. By the variability of the characteristics of rain
detected by chronicles of observed rainfalls or anticipated by atmospheric models and by rainfall-flow modelisation,
impacts on hydrological risk are studied. Moreover, tests on future scenarios are possible, to evaluate the impact of
climate changes and also of landscape use. Our previous research has allowed us to product climatic typology of
rainfall by using model parameter settings. The rainfall and rainfall-runoff models have already been regionalised, with
actual climate hypothesis, on the part of French territory, but also on the Italian piemont , in a Spanish region, in the
Caribbean and on Reunion Island. On these territories, the cartographic evolution of hydrologic risk can be
evaluated with climatic change hypothesis.
 Arnaud P., Fine J.A., Lavabre J., 2007. An
hourly rainfall generation model adapted to all types of climate. Accepted in Atmospheric Research.
P., Lavabre J., 2002. Coupled rainfall model and discharge model for flood frequency estimation. Water Resources
Research, 38(6) 1075-1085.