Hello. It is well-known that renewable energies, such as wind or solar energies, are intermittent. The electricity production depends on rapid variations of wind intensity or solar radiation. In comparison, hydropower is often considered as a steady resource, having low fluctuations, but it is indeed a valuable resource which is subject to weather or climate fluctuations. If we look at the monthly hydroelectric production in France, it varies during the year. The production during the winter and spring months is twice as low as in the summer or fall month. Such seasonal variation is characteristic of hydropower, which accumulates hydraulic energy in dams during winter and release it in summer. This seasonal cycle is well-known and is also found in the rivers flows. If now we look at the annual hydroelectric production in France, we see that it can vary greatly from one year to another. The mean annual production is about 64 terawatt-hour, but it can reach 80 terawatt-hour some years and sometimes fall below 50 terawatt-hour. These interannual variations are about plus or minus 25 percent. If now we look at the United States, these interannual variations can exceed 60 terawatt-hour, which is a total French hydroelectric production. The amplitude of such fluctuations is here, about plus or minus 35 percent, which is far from negligible. What are the main causes of such large interannual variations? It is necessary here to remember how we estimate the hydropower resource. We have seen earlier that hydroelectricity depends at a first approximation on the intensity of the hydrological cycle and the amount of potential energy induced by the transport of water mass on the top of the mountains. The amount of annual precipitation has therefore a direct impact on the hydroelectric production, and the annual average rainfall can vary greatly from one year to another. We find here that the interannual rainfall variations are about 20 percent, which is comparable to variations in the hydroelectric production. Moreover, if we look at the years with low precipitations, it generally corresponds to the years when the hydroelectric production is well below the average. Conversely, years with high rainfall corresponds to the years of high hydraulic reproduction. Since the lifetime of a hydroelectric dam or [inaudible] of power plant generally exceeds half a century one can wonder about the long-term evolution of precipitation and the impact of climate change on the hydroelectric production. The climate change is generally considered as the increase of the mean temperature of the Earth surface, but this increase in temperature is not uniform over the globe. Climate models predict a higher temperature increase on the continents than on the seas. This map shows what will be the geographical distribution of temperature increase at the end of the 21 centuries as a function of the increase of the mean Earth temperature. For example, if we assume that we will succeed in reducing the greenhouse gases emission in order to limit the global warming to two degrees Celsius, the increase of the mean temperature north Africa will be 1.5 times 2 degrees Celsius, which means three degrees Celsius. While in Alaska, the temperature increase will be 2 times 2 degrees Celsius, therefore, four degrees Celsius. A similar map exists for precipitations and depicts the impact of the climate change on the rainfalls. We recover here a very strong spatial heterogeneity; in some regions, increased precipitation are expected ,while in the others, a lack of precipitation is expected. Annual rainfall will decrease in the Mediterranean and increase in Asia, thus at the end of the century if global warming is contained at two degrees Celsius, Morocco will suffer an annual precipitation deficit of minus 9 times 2, which is about 20 percent. But this is an annual average and this precipitation deficit is generally much higher during the summer month when precipitations are low. A higher resolution map of precipitation changes was built for Europe in 2015. The blue areas north-eastern Europe correspond to an increase in the annual precipitation, while the orange-red areas indicate a lack of precipitation. Norway will therefore experience an increase of its hydroelectric production at the end of the century without changing its installed capacity, while Spain should experience a decrease in his production. France is located in a white region, which is a neutral zone where small variations in the annual precipitation are expected. Of course, the amplitude of these hydrological changes will depend on the intensity of the global warming. To conclude, hydraulic resources are highly dependent on the annual rainfalls and are subject to significant seasonal and interannual variations. It is also necessary to anticipate long-term trends related to climate change. Hydroelectricity is a renewable resource that is predictable at short and medium times. The electricity production can generally be predicted over the coming days. It is also a controllable resource because hydroelectric installations allows to regulate the production and very often to store hydraulic energy over long time periods. To understand the different modes of hydroelectric production, I invite you to follow the next sessions. Thank you.
