How will global warming and climate change impact water security?
Global warming and climate change could in fact bring back an old stating back into circulation: “Water, water everywhere but not a drop to drink”
Fresh water is crucial to human society – not just for drinking, but also for farming, washing and many other activities. It is expected to become increasingly scarce in the future, and this could at least partly due to climate change.
Understanding the problem of fresh water scarcity begins by considering the distribution of water on the planet. Approximately 98% of our water is salty and only 2% is fresh. Of that 2%, almost 70% is snow and ice, 30% is groundwater, less than 0.5% is surface water (lakes, rivers, etc) and less than 0.05% is in the atmosphere.
A relevant effect of warming is to increase the amount of water that the atmosphere can hold, which in turn can lead to more and heavier rainfall when the air cools. That sounds like great news, doesn’t it? Global warming could lead to more rains, and that should mean more freshwater, right?
Unfortunately, it might not! Although more rainfall can add to fresh water resources, heavier rainfall leads to more rapid movement of water from the atmosphere back to the oceans, reducing our ability to store and use it. When snow and ice collect on mountaintops, water is released slowly into reservoirs as it melts throughout the spring and summer. With heavy and frequent rain, reservoirs fill quickly to capacity in the winter, which can also result in excess water runoff that can’t be stored. Because rain flows faster than melting snow, higher levels of soil moisture and groundwater recharge are less likely to occur.
Yet another impact of higher temperatures is the melting of inland glaciers. This again sounds like a positive development from a water availability perspective, as this will increase water supply to rivers and lakes. Yes, indeed it will, but what happens when all the glaciers have melted? Essentially, such a rush melting of glaciers could result in an oversupply of water to some regions in the short term (which means the water will be under-utilized) and in the medium and long run, the availability of fresh water from these sources could be curtailed significantly. A really sub-optimal scenario.
Global warming is also expected to lead to reduced rainfall in what are already dry regions, especially the sub-tropics.
The overall effect of all the above phenomena is an intensification of the water cycle that causes more extreme floods and droughts globally, both negatively affecting fresh water availability. That is, even in the short term, some regions will have an oversupply and under-utilization and other regions will have a severe short supply.
Hardly the kind of situation any planner worldwide would wish for!
