Water and climate

The disruption of the water cycle affects all human activity, with global consequences: access to drinking water, health, food security, agriculture, economic development and social progress. By reinforcing inequalities between territories, they threaten the stability of countries.

In the Fifth Report, the IPCC returns largely to this role of water and states that it is "likely that human influence has affected the global water cycle since 1960". Although one of the main limitations of the IPCC's observations, which it mentions, is the difficulty in differentiating the action of climate change from other factors, it notes that "human influence has been detected in the warming of the atmosphere and oceans, in changes in the global water cycle, in the reduction of snow and ice, in global average sea level rise". Water is therefore taking on an increasingly important role in IPCC reports, demonstrating both its role as a "privileged intermediary" for the effects of climate change and as a marker of it. The WGII devotes an entire chapter to it, Chapter 3 "Freshwater Resources", which reports on all the pressures caused or reinforced by climate change.

But water is also present transversally through different chapters. Water is thus directly involved in seven of the eight key risks mentioned:

• Risks in low-lying coastal areas resulting from storms, submersion, sea level rise, impacting livelihoods;
• Risks to large urban populations in flood-prone areas ;
• Systemic disruptions of critical services resulting from extreme events (e.g. drinking water and sanitation services);
• Food insecurity due to drought, in particular ;
• Water scarcity for agricultural populations ;
• Changes in marine and coastal ecosystems affecting Arctic and tropical populations ;
• Impacts on wetland ecosystems and their consequences ;
• The eighth risk cited concerns "heat waves" which also impact water demand and supply.

Above 2°C of warming by reference to 1990, each degree could lead to a 20% reduction in renewable water resources for at least 7% of the world's population. Approximately 80% of the population is already affected by water insecurity (availability, demand, pollution).

Climate change is therefore likely to reduce the planet's renewable water resources (surface and groundwater), exacerbating conflicts between uses, mainly in dry intertropical areas, while in high latitudes, water resources are expected to increase.

The world's demographic dynamism mechanically increases the demand for water and thus the pressure on the resource. In addition to this "digital" growth, there are profound changes in socio-economic structures, technical developments and changes in lifestyles.

Climate change is indeed a determining factor in many regions of the increase in water demand from the agricultural sector, the leading water-consuming sector with 90% of this water devoted to irrigation on a global scale.