Hydrological Cycle: Its Impact on Agriculture

Water is essential for all life – for people, plants, and animals. How much water we have and how we use this water determines the productivity of our land – how many people, plants, and animals it can support. You cannot create or destroy fresh water. There is a limited amount of water on the Earth that flows in a cycle. This cycle is commonly known as the hydrological cycle.

Climate change is affecting when, where, and how much water is available. Subsequently, extreme weather events such as droughts and heavy precipitation severely impact the water resources. Climate changes will lead to an increase in these extreme weather conditions. It can cause a lack of adequate water supplies(water scarcity), flooding, or degraded water quality.

All these factors impact civilization, now and throughout the history of human civilization. These challenges can affect the economy, energy production, usage, human health, transportation, agriculture, national security, natural ecosystems, and recreation. Consequently, it becomes essential to understand the phenomena of the hydrological cycle.

What is a Hydrological Cycle?

The hydrological cycle is also commonly known as the water cycle. It describes the material flow of water throughout the Earth. It comprises a series of steps that explain how water moves across the Earth and changes various forms. These steps result in continuous circulation of water between oceans, the atmosphere, and the land. The hydrological cycle involves natural phenomena that include precipitation, runoff, and storage before finally returning to the atmosphere.

The precipitation can be in snow and rain, and the return of water to the atmosphere through transpiration and evaporation. Throughout the history of Earth, the natural cycling of water through various locations on the Earth has existed. Consequently, it means that the amount of water has been relatively constant. Water is continuously in motion, and little has been added or lost over the years.

Components of Hydrological Cycle 

The hydrological cycle has two primary components, namely, storage and movement. The storage component deals with where water in the system resides or “rests” as it moves from one water body to another. 

For example, water storage in a lake occurs through some movement ie movement of water, such as precipitation in the form of rain. After entering the lake, it stays there for some time in its storage period. Eventually, the water moves back out through some movement, such as discharge into a river, evaporation into the atmosphere, or migration into the subsurface groundwater system.

It is important to note that water changes state from solid to liquid water and from liquid to gas. For changing the state, water requires energy. The evaporation and transpiration from continents and the evaporation of water from the oceans are essential components of the hydrologic cycle that involves a change of state and energy input. Since nature follows the energy conservation law, the energy to fuel this cycle comes from the Sun.

Hydrological Cycle – Water Storage

Water storage in the hydrologic cycle is essential. Water is stored in three main places: the atmosphere, on the surface of the Earth, and underground. These water storage areas are collectively termed reservoirs, including oceans, glacier ice, groundwater, lakes, soil moisture, the atmosphere, and the rivers. Collectively, all the water storage areas make up the hydrosphere. More than 97% of the world’s water is in the oceans as saltwater.

Since the overwhelming majority of water is in oceans, it can be seen as the starting and ending point of the cycle. Water that starts from the sea evaporates up into the atmosphere, where most of it falls back into the ocean as rain. Additionally, a much smaller amount falls onto land as rainfall.

Water moves from one reservoir to another via various transport mechanisms. However, it can stay in storage for varying periods. The water movement can be pretty erratic from place to place, but we have trends for how long certain reservoirs retain their water. The average length of time that water remains in any reservoir in the hydrological cycle is defined as the residence time.

The soil moisture lasts a couple of months, while water in the atmosphere gets renewed every fortnight. Replenishing water in great lakes happens every 50 to 100 years, while groundwater lasts anywhere from 100 to 10 000 years. The ice caps hold water the longest, with residence times of up to 200 000 years.

The geologic features related to the soil types and the nature of underground rocks present at the storage locations decide the type of storage on the land surface and below the ground.

Hydrological Cycle – Water Movement

There are different ways that water moves across the planet in the water cycle. All of these different movement methods are important in maintaining water levels in certain locations around the globe, evaporation condensation is one such cycle.

Evaporation

The sun’s rays heat oceans, ponds, lakes, rivers, and other water bodies. Water evaporates and rises into the atmosphere as water vapor. 97.5% of the earth’s water is in the ocean, so a large amount of water enters the atmosphere through evaporation at the ocean’s surface.

Evapotranspiration

When water vapor leaves a vegetated surface in a practical scenario, it is generally difficult to distinguish between transpiration from plants and evaporation from the soil surface. Therefore, these combined processes are commonly termed evapotranspiration.

Impact of global temperatures on Hydrological Cycle

The hydrological cycle largely depends on the solar energy received by the Earth. Higher temperatures result in more evaporation, condensation precipitation, and higher humidity. Global warming is likely to significantly affect the hydrological cycle due to the emissions of greenhouse gases. Since a warm Earth means a moist atmosphere, the hydrological cycle will become more intense. Consequently, the precipitation and river flow will increase by 10% to 40% in tropical locations.

Additionally, the forecast points to a decrease in precipitation up to 30% in dry locations/ Therefore, floods will become a regular feature in areas with more rain. At the same time, droughts will affect arid places. The frequency of hurricanes and typhoons is very likely to increase.

Role of  Hydrological Cycle in Agriculture

Some portion of precipitation infiltrates into the soil. It is ok for the infiltration rate of the soil to be less than the rainfall intensity. In such a scenario, excessive precipitation becomes runoff, which is one of two causes of erosion. Not all runoff reaches the ocean. Some evaporate while some are collected in different size impoundments. Some infiltrate into the soil, and the vegetation uses some portion. The water used by plants may disappear quickly, or it may become part of the plant processes. Water can remain in plants for extended periods, but it eventually returns to the hydrological cycle.

The precipitation which infiltrates into the soil also takes different paths. Some fall on areas of deep soil and percolates deeply into the earth. Other infiltration may reach an impervious layer close to the surface and start moving horizontally at a rapid pace. The underground horizontal movement may end at some surface water or flow out of the ground as a spring or an artesian well. It may eventually land up in the ocean. Horizontal movement through the soil may be as ver slow as a few inches per year. Once the water reaches the sea, the sun causes it to evaporate, and the cycle begins again.

Water Conservation and Hydrological Cycle

You can use the hydrologic cycle to explain the importance of water conservation. Activities such as pumping, dam building change the amount and direction of the flow of water. Any water captured by a dam not only reduces the amount of water available to downstream users. Additionally, it also changes the amount of water that infiltrates into the soil and evaporates into the atmosphere and this water vapor condenses to form rain. Contamination, in the form of chemicals, silt, and so forth, added to the water at one point in the cycle may remain in the water and cause problems for the following user.

Agricultural practices may also have negative impacts on water quality. Improper agricultural methods may elevate concentrations of nutrients, fecal coliforms, and sediment loads. Increased nutrient loading from animal waste can lead to eutrophication of water bodies which may eventually damage aquatic ecosystems.

Conclusion

Water influences the intensity of climate variability and change. It is the key part of extreme events such as drought and floods. Its abundance and timely delivery are critical for meeting the needs of society and ecosystems.

We use water for drinking, industrial applications, irrigating agriculture, hydropower, waste disposal, and recreation. It is essential to protect water sources both for human uses and ecosystem health. In many areas, the depletion of water supplies occurs due to population growth, pollution, and development. These stresses have been made worse by climate variations and changes that affect the hydrologic cycle.