Climate change and impacts on water

Climate can be defined as the set of meteorological phenomena that define the average state of the atmosphere in a given locality at a given time. In the current state of knowledge, it remains complicated to establish the dynamics of an average climate for planet Earth. However, it would seem that all scientists agree that global warming is underway, and that most of them see a direct implication of carbon dioxide emissions into the atmosphere as a result of human activity. Thus, the observation of changes in the average state of the Earth's atmosphere seeks to find justification in the interactions with all the Earth's components: the atmosphere, the hydrosphere, the biosphere and the lithosphere. For over 10 years, the experts of the IPCC (Intergovernmental Panel on Climate Change) have been working to explain the facts and predict the future climate, for whom "warming of the climate system is unequivocal". The IPCC's successive reports, the first of which was completed in 2001, demonstrate this assertion through the strong correlation between changes in atmospheric CO ₂ content, linked to the explosion in fossil fuel consumption since the early 20th century, and rising air temperatures.

However, while the core of certainties is growing, controversies persist. Scientists are also showing that atmospheric CO ₂ content alone cannot account for the variation in mean temperature, explaining at the same time the current slowdown in warming despite the growth in CO ₂ content in the atmosphere. Against this backdrop of certainties and uncertainties, international and national measures to limit the impact of climate change are struggling to get off the ground. These actions can be classified into two broad categories: mitigation and adaptation. Does the level of uncertainty and certainty affect the implementation of these measures? What about water resources?

The most foreseeable consequences, particularly for coastal areas, concern sea-level rise. However, the implications are far-reaching for the entire water cycle: evaporation, precipitation, runoff and marine intrusion. Hydrological modelling, coupled with climate modelling, therefore seeks to predict the impact of these climatic changes on hydrosystems. Given the current state of knowledge, where do the greatest uncertainties lie today: in climate change or in the impact on the hydrological cycle?

After describing the certainties and uncertainties in the observed and projected climate change phenomena, this article will focus on the impact of climate change on the water cycle. What will be the scale of the changes? How can freshwater use be regulated in...