Mountains have been the source of inspiration to human beings in history, with their magnificence and great silence. As the famous mountain photographer Ansel Adams said, "No matter how sophisticated you may be, a large granite mountain cannot be denied - it speaks in silence to the very core of your being.” On the other hand, one of the attributes of our Almighty Creator is to tie many different purposes to a single creation , and mountains are no different. For a geologist, mountains are like “water towers of the world.” We may have seen man-made water towers in cities. They are water storages which are built purposefully tall, perhaps taller than any other buildings in the city. The function of these water towers is to store enough water to provide the residents of the city a consistent supply of water for one day during the maximum (day) and minimum (night) usage times. The “water towers of the world” act in the same way for the people of the Earth, but on a yearly basis instead of a daily basis.
On the face of the Earth, mountain regions are defined as areas more than 1000 m in elevation. Although mountains cover only 27% of the total land area of the planet, the percentage of the world population who are dependant on the mountains is much larger. In terms of water dependency, about 70% of the population uses water originated in the mountains. This ratio becomes close to 100% in arid regions. Interestingly, the water towers of the world are generally located in the arid regions of the world. It is not unusual to see an arid lowland region with a big river crossing it. These regions are usually connected to a nearby mountain from which the river originated. The significance of the mountains is mentioned in the Bible as the following: "For the Lord is the great God, the great King above all gods. In his hand are the depths of the earth, and the mountain peaks belong to him. The sea is his, for he made it, and his hands formed the dry land” (Psalm 95:3-5).
All great rivers of the world originate in mountains. For example, the arid region of Central Asia is watered by the Tarek, Amu Darya, and Tarim Rivers. All of the big rivers of China and India originate in Tibet. Pakistan is dependant on the Indus River. Asia Minor and Northern Arabian Peninsula are supplied by Euphrates and Tigris Rivers while Northern Africa is supplied by Nile River. All Australian waters are supplied by rivers originating from eastern highlands, and Europe is supplied by the Po, Rhine, and Tiber Rivers, which originate in mountainous areas. This makes mountain water strategically important in these areas, and in fact, some countries prefer to keep their need of mountain water a secret!
Here it is worth discussing the global water cycle in order to understand the peculiar role of the mountains. All of the precipitation onto land comes from evaporation on land and oceans. A significant portion of the land precipitation goes back to seas and oceans via river discharge every year. And the main source of fresh water for humans and other living organisms comes from rivers. For low-land precipitation (as opposed to mountain precipitation) the discharge happens rather quickly, within weeks. Therefore, humans build dams in order keep the water for longer periods of time. Another longer term solution to keep more water on land is planting trees, which benefits not only humans but all other living creatures!
For mountains, the water cycle works quite differently. Since the mountains are in high elevations, precipitation starts early in the late fall and continues until the end of spring. The river discharge does not begin until early summer. Especially in arid regions, the low-land discharge mostly diminishes by early spring, and no predictions can be made as to how arid the coming summer will be. On the other hand, because of lower temperatures in the mountains, evaporation is also minimal, which makes them efficient natural storages. At the end of spring when the lowland precipitation starts to diminish, the mountain water discharge begins in a steady manner and continues during the entire summer season. When we look at the yearly usage of water even in a humid region like Europe, more than 50% of the water during the hottest and driest months of June and July is released from the Alps. This percentage is more than 95% in arid regions of the world, such as Mesopotamia and North Africa. The Holy Quran mentions the storage of bounties, including water, explicitly as the following: "There is not a thing but the stores (for its life and sustenance) are with Us, and We do not send it down except in due, determined measure. And we send the winds to fertilize; and so We send down water from the sky, and give it to you to drink; it is not you who are the keepers of its stores” (15/21-22).
Since lowland water discharge is mainly controlled by precipitation, it is also unpredictable and rather quick. This is particularly inconvenient for farmers who have to make business plans for the entire of the year ahead of time. The knowledge of yearly precipitation is vital for farmers to make reliable investments. In lowland areas, prediction of water distribution months in advance is very difficult, and almost impossible before it actually precipitates! (In fact, an area of geological sciences is devoted to forecasting precipitation. This is also important for preventing causalities in potential floods). On the other hand, mountain discharge offers stability during the year, which makes life much easier for farmers.
Mountains are generally seen in our distant horizons of our living areas with their magnificence and silence. They have many benefits that we may or may not be aware of. Indeed they are the water towers of the world.
H. Huseyin Erdem is an earth scientist living in the USA.