Global Water Distribution

Global Water Distribution

Introduction

Amazingly, water (H2O) is a material. When compared to similarly related chemicals like hydrogen sulfide (H2S), which is a gas at room temperature, it is uncommon enough that it is a liquid at ambient temperature. It is easy to understand why people are captivated by it when you consider that many substances can dissolve in the liquid and that the solid form (ice) is less dense than the liquid. Water, however, is more important than this for life as we know it. Water is frequently used by astronomers as a clue that life may exist outside of our solar system. The discovery of water on Mars recently has fueled the idea that life may be present there now or may have existed there in the past.

Importantly, water is translucent. According to our estimates, life on Earth began in the sea approximately 3 billion years ago and only appeared on the land about 600 million years ago. Green plants use light to perform photosynthesis, a process that is essential for life. The development of photosynthetic creatures in the sea thousands of millions of years ago would have been possible if water had the ability to allow at least some light to pass through it. Water is a great supply of tiny molecules because it can dissolve a wide variety of compounds, including the minerals and carbohydrates needed for life.

The World Health Organization (WHO) is worried that not enough people have basic access to hygienic facilities and clean water to drink. The WHO's Director for Public Health, Dr. Maria Neira, stated in May 2014 that far too many people do not have access to even the most basic sanitation and drinking water facilities. Life depends on water, which is necessary both in large quantities and, more crucially, in high quality. We mistreat and contaminate water despite how much we depend on it, both personally and nationally.

1. Water Distribution

Only 3% of the water on Earth's surface is fresh (not salty) and potentially usable by humans, despite the fact that more than 75% of its surface is covered by water. 42 million km3 or thereabouts of freshwater is involved, however, much of this water is trapped in glaciers or polar ice caps. In actuality, less than 1% of the fresh water on Earth is accessible to humans.

Source: IGCSE Environmental Management textbook

The distribution of the Earth’s water

This is equivalent to 420 000 km3, or around 60 million litres of water for each person on Earth. An individual uses, on average, 1.5 million gallons of water annually. This occurs both directly – for drinking and cleaning, for instance – and indirectly – during the production of goods that people consume. Even if it appears like there is enough water for everyone, the reality is more complicated. Only six countries contain half of the world's freshwater supply: Brazil, Russia, Canada, Indonesia, China and Colombia. Furthermore, much of it is unfit for consumption. Consequently, supplying clean enough, safe water for everyone is difficult.

Water collection is a responsibility that women bear on a global scale and can take up to 6 hours each day. In Africa and Asia, women must go 6 kilometers on average to obtain water. According to a Tanzanian study, girls' school attendance increased by 12% when the time required to get water was cut by 15 minutes. Women who collect water may need more time to get a thorough education. The Water Cycle

Introduction

All the water on Earth passes through the water cycle all the time. In this section we look at the water cycle, how each step in the cycle works, and why the water cycle is so important to us.1. What is the Water Cycle?

The amount of water on Earth, 1 386 000 000 km3, is a constant that does not change throughout time. Water, however, may be found anywhere and comes in a variety of shapes. A specific water molecule may be present in a raindrop one moment and in glacier ice the next. It can be in a swift-moving northern river or the ocean. A shift in the location of water is frequently caused by a change in its state. A glacier's ice may melt and turn to liquid water. Then it can go into a river that empties into a lake. Water may evaporate and turn into vapour when the sun's warmth is applied to the lake.

After rising into the sky, this vapour may condense to form clouds. Precipitation is the term used to describe when the water in these clouds turns into rain or snow. It might then permeate the soil and be absorbed by a plant's roots, which would then carry it up the plant in the stream of transpiration. The loss of water by the plant during transpiration is what propels this movement. Other possibilities include that it will run off the surface of the ground in a process known as surface runoff, be intercepted by plant leaves, enter the ground through infiltration, and then become a part of groundwater flow (if it flows through rocks) or throughflow (if it flows through soil).

The main processes in the water cycle

2. The Processes in the Water Cycle

There are various processes present in the water cycle, namely:

evaporation condensation precipitation transpiration surface runoff interception infiltration groundwater flow, and throughflow. Let's have a look at each of these in greater detail.

2.1 Evaporation

Evaporation is the process by which a liquid, such as water, turns into a gas, such as water vapour, due to the input of energy, typically heat. During evaporation, the molecules of a liquid gain enough energy to break their bonds and escape into the surrounding environment as a gas.

An example of evaporation in the water cycle is when the sun heats up water in oceans, rivers, and other bodies of water, causing it to evaporate and turn into water vapour. This water vapour rises into the atmosphere and forms clouds. Without evaporation, water cannot enter the atmosphere and form clouds, which are an essential part of the water cycle that eventually leads to precipitation and the replenishment of the Earth's water supply.

2.2 Condensation

Condensation is the process by which a gas, such as water vapour, turns into a liquid, such as water, due to a decrease in energy, typically a drop in temperature. During condensation, the molecules of a gas lose energy and come together to form a liquid.

An example of condensation in the water cycle is when water vapour in the atmosphere cools down and condenses into tiny droplets, forming clouds. As more water vapour condenses onto these droplets, they grow larger and heavier until they fall to the Earth's surface as precipitation, such as rain, snow, sleet or hail. Without condensation, there would be no clouds to produce precipitation, and the water cycle would not be able to provide the Earth with the freshwater that is essential for life.

2.3 Precipitation

Precipitation is the process by which water falls from the atmosphere to the Earth's surface in the form of rain, snow, sleet or hail. It occurs when the air becomes saturated with water vapour, which condenses and forms clouds. When the clouds become heavy with water droplets, the water falls back to the ground as precipitation.

An example of precipitation in the water cycle is when water vapour in the atmosphere condenses into clouds. When the clouds become too heavy with water droplets, they release the water back to the Earth as precipitation. For instance, rain falls from the clouds and onto the ground, replenishing rivers, lakes, and other bodies of water. Snowfall is another form of precipitation, which occurs when water vapour freezes into ice crystals in the clouds and falls to the ground.

2.4 Transpiration

Transpiration is the process by which plants absorb water through their roots and release it into the atmosphere through their leaves as water vapour. It is similar to evaporation, but it specifically refers to the water loss from plants. Transpiration helps to regulate the water cycle by returning water to the atmosphere, where it can be recycled and used again.

An example of transpiration in the water cycle is when water is taken up by the roots of a plant and transported up to the leaves. Once in the leaves, the water evaporates and is released into the atmosphere as water vapour. This water vapour can then condense and form clouds, which can lead to precipitation, continuing the water cycle. Additionally, the water that is taken up by plants can also be used by animals that consume the plants, completing the cycle of water through living organisms.

2.5 Surface runoff

Surface runoff refers to the movement of water across the surface of the Earth, often caused by precipitation or melting snow, that does not infiltrate into the ground. Instead, it flows over the land and eventually makes its way into rivers, lakes and other bodies of water.

An example of surface runoff in the water cycle would be when rain falls on the ground and runs downhill into a nearby river or stream. This water may also collect in puddles or form small streams or creeks as it flows across the land. Surface runoff plays an important role in replenishing water sources and supporting the natural ecosystem, but it can also lead to erosion and pollution if not properly managed.

2.6 Interception

Interception refers to the process by which precipitation, such as rain or snow, is caught and held by the leaves, branches and stems of plants before it reaches the ground. This intercepted water can then evaporate, be taken up by the plants, or slowly release into the soil.

An example of interception in the water cycle would be when rain falls on a forest canopy. The leaves and branches of trees act as interceptors, catching and holding the rainwater. Some of this water may evaporate directly from the leaves, while some of it may trickle down the stems and branches and eventually enter the soil. This process is important for sustaining the health and growth of plants, and also for regulating the flow of water through the ecosystem.

2.7 Infiltration

Infiltration refers to the process by which water from precipitation or snowmelt penetrates into the soil and percolates downward through the soil layers, ultimately becoming groundwater. It is an essential component of the water cycle, as it replenishes groundwater and provides moisture for plant growth.

An example of infiltration in the water cycle would be when rain falls on the ground and seeps into the soil. The water may initially collect in small depressions or pores in the soil, but will eventually move downward due to gravity and capillary action, where it will become part of the groundwater system. The rate of infiltration can be affected by factors such as soil type, vegetation cover, and the intensity and duration of rainfall. Infiltration is an important process for replenishing aquifers and sustaining the health of ecosystems that rely on groundwater.

Infiltration is the entry of water into the soil surface, while percolation is the downward movement of water through the soil profile.

2.8 Groundwater flow

Groundwater flow refers to the movement of water within the underground aquifer system. It is an essential component of the water cycle, as it plays a critical role in regulating the flow of water through the environment.

An example of groundwater flow in the water cycle would be when water that has infiltrated into the soil moves downward and collects in underground aquifers. This water may then flow through the aquifer system, eventually discharging into surface water bodies such as streams, rivers and lakes. Groundwater flow is influenced by factors such as the permeability and porosity of the underground geology, the elevation of the water table, and the presence of underground aquifers or channels. It is an important process for sustaining the water supply for human and ecological needs, and for maintaining the balance of the water cycle.

2.9 Throughflow

Throughflow refers to the movement of water within the soil, from the point of infiltration to the point where it enters the stream or groundwater system. Throughflow occurs when the soil becomes saturated and cannot hold any more water, causing the excess water to flow laterally through the soil layers.

An example of throughflow in the water cycle would be when rainwater infiltrates the soil and moves downwards until it reaches an impermeable layer, such as rock or clay. When this layer is reached, the water cannot move any further downwards and begins to flow laterally through the soil layers, eventually reaching a stream or groundwater system. The movement of water through the soil layers in this way is known as throughflow.

Throughflow is an important process in the water cycle as it can transport water and nutrients through the soil, influencing plant growth and the availability of water resources for human use.