ANÁLISIS HORIZONTAL DEL BALANCE GENERAL Y ESTADO DE RESULTADOS DEL BNF SUC ZARUMA AÑO 2009.

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UNIT 2 HYDROLOGY AND WATER CYCLE

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total amount of water on earth remains about the same(>1,404 million km³ or 370 billion gallons) from year to year but water moves from one compartment to another (compartments e.g seas, rivers etc).

The hydrologic process supplies fresh water to land masses and plays an important role in creating a habitable climate and moderating temperature all over the world.Water movement back to the seas and glaciers are important forces which shape the land masses and re-distribute materials.

Plants absorb water from the ground and pump it into the atmosphere through the process called transpiration. This process involves evaporation of water from plant and soil surfaces and is described as evapotranspiration.Water evaporates as water vapor into the air. Ice and snow can sublimate directly into water vapor. About 75% of annual precipitation is returned to the atmosphere by plants. Solar energy drives the hydrologic cycle by evaporating water from surfaces. All the physical, chemical and biological processes involving water as it travels in the atmosphere, over and beneath the Earth’s surface and through growing plants are important in the hydrologic cycle.

There are many pathways that the water molecules may take in the continuous cycle of preciptation and returning to the atmosphere. It may take millions of years as when resident in ice caps or flow through rivers into the seas. It may soak into the soils (infiltration) and later be evapoated from the soil surface into the atmosphere or indirectly through plants (tranpiration) back into the atmosphere. It may percolate through the soil into the groundwater aquifers or reservoirs or may flow into streams, rivers or springs.

Water is tapped for use in homes, industries and used water is returned to the cycle by discharging into streams or on the soil surface from where it can evaporate or sink into the soil.The processes involved in the water cyle include evaporation, precipication, groundwater flow and other components.

The hydrologic cycle also involves the exchange of heat energy which causes temperature changes. For example, during evaporation, water takes up energy from the environment and this cools the environment. On the other hand, during condensation, water releases energy to its surroundings causing warming. The water cycle is important in maintaining life on earth.

By transfering water from one place to another, or one reservoir to another, the water cycle purifies the water, replenishes the land with fresh water and transports minerals to different parts of the world. The water also reshapes

57 the geological features of the earth through erosion and sedimentation. The water cycle also influences the earth’s climate due to heat exchange.

In the hydrologic cycle, water moves constantly between aquatic, atmospheric and terrestrial compartments driven by the solar energy and gravity. The total annual run off from land to the oceans is about 10.3 x 10¹⁵ gallons.

3.2 Description of the Water Cycle

Rising air currents take the vapour up into the atmosphere where cooler temperatures cause it to condense into clouds. Air currents move water vapour around the world; cloud particles collide, grow, and fall out of the sky as precipitation. Some precipitation falls as snow or hail, and can accumulate as ice caps and glaciers (store frozen water for thousands of years).

Snow packs thaw, melt, and the water flows over land as snowmelt. Most water falls back into the oceans or onto land as rain, where the water flows over the ground as surface runoff. Some runoff enters rivers and flow towards the oceans. Runoff and groundwater are stored as freshwater in lakes. Part of the runoff flows into rivers, some soaks into the ground as infiltration. Some water infiltrates deep into the ground and replenishes aquifers (store freshwater for long periods of time). Some infiltration stays close to the land surface and can seep back into surface-water bodies (e.g.

the ocean) as groundwater discharge. Some groundwater finds openings in the land surface and comes out as freshwater springs. Over time, the water returns to the ocean and the cycle starts again.

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Fig 5: Schematic Representation of the Water or Hydrologic Cycle (Source:Domenico and Schwartz,1990)

The hydrologic cycle begins with the evaporation of water from the surfaces of the ocean and earth. As moist air is lifted, it cools and water vapour condenses to form clouds. Moisture is transported around the world and then returns to the surface as precipitation. On reaching the surface, 3 processes may occur:

1) Evaporation of water back into the atmosphere.

2) Penetration of water through the surface into the groundwater through a process called infiltration. Groundwater may seep into the oceans, rivers and streams or is released into the atmosphere through transpiration.

3) The balance of the water that remains on the earth’s surface is the runoff which enters lakes, rivers, streams and is carried into the oceans where the cycle begins again.

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3.3 Changes in the Hydrologic Cycle over Time

The water cycle describes the processes that drive the movement of water throughout the hydrosphere. The storehouses for most of the water on Earth are the oceans. It is estimated that about 95% of the 1,386,000,000 km³ (world's water supply), is stored in oceans. The oceans supply about 90% of the evaporated water that enters the water cycle.

Ice caps and glaciers accumulate in the cold seasons and reduce the amounts of water in the other compartments but the ice melts in warm periods ice storage reduces and water contents of other compartments increase.

3.4 Impacts of Human Activities on the Water Cycle

Human activities that affect the global water cycle in some important ways include agriculture, industry, alteration of the chemical composition of the atmosphere, construction of dams, deforestation, aforestation, removal of groundwater from wells, water abstraction from rivers and urbanisation.

1) One of the main sources of atmospheric water is transpiration from the dense vegetation making up tropical rain forests. Deforestation changes the amount of water vapour in the air. This in turn most likely alters local and global weather patterns.

2) Another change in the water cycle caused by humans results from pumping large amounts of water from groundwater to use for irrigation and domestic purposes. This can incease therates of evaporation over land and unless this loss is balanced by an increased rainfall over land, groundwater supplies will get depleted.

3) The water cycle drives the movement of water through out the hydrosphere.Much of the water is stored in different compartments.

4.0 CONCLUSION

The water cycle is important for the circulation of water on earth among all the compartments. This cycle is driven by the solar energy and makes water available to man and other living organisms.

5.0 SUMMARY

In this unit, we discussed the hydrological cycle, changes in the cycle over time and the human influences that have affected the cycle over time.

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6.0 TUTOR –MARKED ASSIGNMENT 1. Explain the hydrologic or water cycle.

2. Discuss the changes in the hydrologic cycle over time.

3. Explain the impacts of human activities on the water cycle.

7.0 REFERENCES/FURTHER READING

Arctic Climatology and Meteorology. Condensation. Retrieved on 2006-10-24.

Dr. Art's Guide to Planet Earth. The Water Cycle. Retrieved on 2006-10-24.

http://ga.water.usgs.gov/edu/watercycleoceans.html USGS, The Water Cycle: Water Storage in Oceans - Retrieved on 2008-05-14

Jouzel, J.; Masson-Delmotte, V.; Cattani, O.; Dreyfus, G.; Falourd, S.;

Hoffmann, G.; Minster, B.; Nouet, J. et al. (2007). "Orbital and Millennial Antarctic Climate Variability over the Past 800,000 Years". Science 317 (5839): 793–796.

Ohio State University Extension Fact Sheet. Nitrogen and the Hydrologic Cycle. Retrieved on 2006-10-24.

PhysicalGeography.net. Introduction to the Hydrosphere. Retrieved on 2006-10- 24.

Strobel, N. (2010). "Planetary Science". Accessed on September 28, 2010.

Dvořák, R. (2007). Extrasolar Planets. Wiley-VCH. pp. 139–140.

Retrieved 2009-05-05.

Wikipedia .org accessed on 6^th March, 2011 Water cycle. (2009). Science Mission Directorate. Retrieved on 7^th January,2009.

Wikipedia Free Online Dictionary, retrieved on 12^th October, 2012

United States Geological Survey (2013).What is hydrology and what do hydrologists do? USGS, US Department of Interior.

http://ga.water.usgs.gov/edu/hydrology.htm accessed 29^th January, 2013.

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UNIT 3 TRANSPORT AND EXCHANGE PROCESSES