1. Unit 1 The Hydrologic Cycle
Prepared and Presented by: Nelsa English
Course: Water Resources: Conservation and Management (ENVS 4114)

2. Importance of Water “Water is Life”
All living things depend on Fresh Water
Salt content < 1% or 1000ppm
Blue and Green water
In Humans water composes
69% of the human body
85% of the brain
35% of bones
83% of blood
90% of liver
All terrestrial biota, ecosystems, and humans depend on fresh water.
The flow of water vapour in the form of transpiration, interception and evaporation from the soil, water bodies, and vegetation is considered green water and runoff and groundwater recharge is considered blue water

3. Importance of Water Contd.
Function of water in the human body
aiding in digestion and absorption of food
regulates body temperature and blood circulation
carries nutrients and oxygen to cells
removes toxins and other wastes
cushions joints and protects tissues and organs, including the spinal cord, from shock and damage

4. Importance of Water Contd.
Function of Water in Plants
Plants consist of 85-98% water
Growth
Production of sugars
Fills new plant cells
Turgidity
Acts as a transport mechanism
Cooling via transpiration
Plants grow because of photosynthesis, which is uptake of CO2 for the production of sugars (carbohydrates or assimilates). These consist of carbon (C), hydrogen (H) and oxygen (O). Both H and O are obtained from water.
Water contributes to plant growth is by filling new plant cells. This causes an increase in weight (growth) mainly at night. Although much water is taken up at day, it does not directly make the plant grow, as the water uptake at daytime is needed to compensate for the water loss by transpiration. At night, in contrast, the transpiration is very limited as there is no sun shine. This avails most of the water taken up for growth, which results in an increase in plant weight mainly at night.
Water facilitates all internal transport in plants. Plants are built out of carbon (C), hydrogen (H), oxygen (O) and about 15 mineral elements (N, P, K, S, K, Ca, Mg, Fe etc.). These elements are suspended in water and absorbed through the roots and moved up throughout the plant via xylem flow. Following photosynthesis, sugars made are again dissolved in the Phloem (water) and transported from the leaves to the growing section of the plant or areas of storage. Water also facilitates the transport of amino acids and plant hormones.
Water provides firmness to the plant cells by putting an outward pressure on the cell walls. This pressure and the firmness are called ‘turgor’. Turgid plant cells are pumped full with water and cannot be compressed.
Leaves exposed to the sun would get overheated if they were not cooled by water evaporating from the leaves. This is facilitated via transpiration.

5. Importance of Water Contd.
4 Main Function of water
Health
Habitat
Carrier
Production
Biomass production
Societal production
Safe drinking water is a fundamental need or precondition for socio-economic development.
Water bodies host aquatic ecosystems and are easily disturbed when water in the water bodies get polluted.
Water transports dissolved and suspended materials picked up by mobile water along its pathways whether it be through the atmosphere, water courses, and landscape. This function plays a central role in land degradation processes inclusive of leaching of nutrients, sedimentation, and erosion.
Aids in economic development. This is facilitated in two ways:
Biomass production which is operated by the flow of “green” water entering through roots and leaving the foliage.
Societal production which is in households and industries and based on “blue” water withdrawn while passing through the landscape and delivered to cities and industries via water supply system.

6. Earth’s Water Distribution
Of all water on earth about 3 % is fresh water and of the 3 % that is fresh water about 1% of this is accessible fresh water

7. Earth’s Water Distribution

8. The Final Picture

9. Hydrologic Cycle Water exists in varying forms
Constantly changing state
Never changing volume
Movement of water through phases- Hydrologic/Water Cycle
Water exists on earth as a solid (ice), liquid or gas (water vapor) . Oceans, rivers, clouds, and rain, all of which contain water, are in a frequent state of change (surface water evaporates, cloud water precipitates, rainfall infiltrates the ground, etc.). However, the total amount of the earth's water does not change.
The movement of the water through the three states is cyclic and therefore is called the hydrologic/water cycle. The basic cycle consists of water rising to the atmosphere via evaporation or transpiration and it returning to the land and ocean via condensation and precipitation.

10. Components of Water Cycle
Evaporation
Change in energy state
conversion of water from a liquid into a gas
Transpiration
Humidity
Relative Humidity
Water is transferred from the surface to the atmosphere through evaporation, the process by which water changes from a liquid to a gas.
There is a weak attraction holds water molecules together. As temperature increases water molecules gain enough energy to overcome the weak force holding them together. This allows molecule to break way from each other entirely and enter into the atmosphere.
Approximately 80% of all evaporation is from the oceans, with the remaining 20% coming from inland water and vegetation via transpiration.
Humidity is a measure of the amount of water vapour in the air. Relative humidity is the amount of water vapour as a percentage of what the air can hold as a particular temperature. Temperature and Relative humidity are directly related.

11. Components of the Water Cycle
Condensation
Lower energy state
Cooling of water vapour
Formation of clouds, fog, or dew
What is formed depends on where the water vapour cools
Condensation occurs when the temperature of the air or earth changes. Water changes states when temperatures fluctuate. Condensation is the change of water from its gaseous form (water vapor) into liquid water. Condensation generally occurs in the atmosphere when warm air rises, cools and looses its capacity to hold water vapor.
If the droplets form in the atmosphere the result is clouds or fog. Fog is generally formed when cool very close to the earths surface (in other world fog is just a very low cloud)
If the droplets of condensing vapour cools on the cool surface of vegetation the result is dew.

12. Components of the Water Cycle
Precipitation
Return of water to earth’s surface
Intensified condensation
Cold Fronts
Forms of Precipitation
Rain (Primary form)
primary mechanism for transporting water from the atmosphere to the surface of the earth.
When Relative Humidity reaches 100% and cooling continued condensation occurs and clouds form. With intensifying condensation water droplets become large enough to fall as precipitation. Rain-causing events are usually as a result of cold fronts. As a cold front moves into an area the warm moist air already in the area is forced upwards. Which results in cooling and eventually precipitation.
The primary form of precipitation in Jamaica is via rainfall however, there are other forms of precipitation these include; hail, snow, sleet, and freezing rain. Amounts of precipitation can vary by location, Amounts of precipitation also vary from year to year

13. Components of the Water Cycle
Water over and through the Ground
Infiltration
Capillary water
Gravitational water
Ground water
Runoff
WATERSHED
As precipitation occurs and contacts the earth’s surface, it may follow one of two pathways. If it soaks into the ground it is called infiltration, if it runs off the surface it is termed runoff. Water that infiltrates has 2 more alternatives.
It maybe held in the soil, the amount held depends on the water holding capacity of the soil. This water that is held cohesively as a continuous layer around soil particles and in spaces is termed “Capillary Water”. This water usually returns to the atmosphere via evaporation from soil, transpiration through plants (green water flow) or a combination of both.
The second alternative is percolation (blue water flow). Infiltrating water that is not held in the soil is called “gravitational water” because it trickles or percolates down through the pores or cracks under the pull of gravity. As it moves it eventually encounters an impervious layer of rock or dense clay where it accumulates completely filling the available space above this layer. This accumulated water in called “Groundwater”. Groundwater moves laterally as it seeks its lowest level. Ground water moves through aquifers until it finds some opening to the surface in the form of seeps or springs. Springs and seeps feed streams, lakes, and river, thus ground water joins ro become a part of surface water where the cycle begins again via evaporation.
Infiltration occurs when precipitation seeps into the ground. This depends a lot on the permeability of the ground. Permeability is the measure of how easily something flows through a substance. The more permeable, the more precipitation seeps into the ground. If precipitation occurs faster than it can infiltrate the ground, it becomes runoff. Runoff flows over the surface of the ground and makes its way into streams and rivers, which in turn make their way to the seas or oceans, where the cycle begins again with evaopration.
All the land area that contributes water to a particular stream or river is referred to as the Watershed.

14. The hydrologic cycle begins with the evaporation of water from the surface of the ocean. As moist air is lifted, it cools and water vapor condenses to form clouds. Moisture is transported around the globe until it returns to the surface as precipitation. Once the water reaches the ground, one of two processes may occur; 1) some of the water may evaporate back into the atmosphere or 2) the water may penetrate the surface and become groundwater. Groundwater either seeps its way to into the oceans, rivers, and streams, or is released back into the atmosphere through transpiration. The balance of water that remains on the earth's surface is runoff, which empties into lakes, rivers and streams and is carried back to the oceans, where the cycle begins again.

15. Questions to Ponder
What would happen to the planet if the hydrologic cycle stopped functioning? What would happen to societies as the supplies of water diminished? Would our planet die?
What would happen if the polar icecaps melted and the hydrologic cycle couldn't keep water levels stable? Where would we go as water levels rose out of control?
Could we ever use the ocean to supplement or water once freshwater disappears? What ways could the oceans be used to provide us with a source of water?