Consumptive use of Water | Civil Engineering Optional Notes for UPSC PDF Download

Evapotranspiration

• Definition and components: Evapotranspiration (ET) is the combined process of evaporation from the earth's surface (water bodies, soil) and transpiration from plants.
• Process of transpiration: Plants absorb water through their roots, which moves up the stem and is released as water vapor through the leaves. This process is driven by osmotic pressure, diffusion, and vapor pressure gradients.
• Evaporation from soil: A portion of soil water also evaporates directly into the atmosphere, contributing to ET.
• Measurement: ET can be measured using specialized instruments like irrigation controllers, which estimate the water loss based on meteorological data.

Significance of Evapotranspiration

• Replenishing freshwater supplies: ET plays a crucial role in the hydrological cycle by returning water vapor to the atmosphere, which can condense and replenish freshwater resources through precipitation.
• Water resource management: Accurate estimation of ET is essential for efficient irrigation and water distribution planning, as well as for assessing environmental impacts on surface and groundwater quantity and quality.

Consumptive Use

• Definition: Consumptive use refers to the amount of water needed by plants for transpiration and the water lost through this process. It is the portion of water that is "consumed" and cannot be reused or recovered.
• Quantification: Consumptive use is expressed as a volume per unit area or the aquatic depth of the irrigated area.
• Return flow: Water that does not evaporate, transpire, or get consumed by plants may seep back into the ground and return to aquifers, known as "return flow."

Factors Affecting Consumptive Use

• Soil type and topography: The nature of the soil and the topography of the area influence water retention and movement, affecting consumptive use.
• Water supply: The availability and quality of water resources impact irrigation requirements and consumptive use.
• Climate factors: Temperature, humidity, sunlight, and wind movement are the most influential climate factors affecting consumptive use through their impact on evapotranspiration rates.

• Irrigation planning: Determining the consumptive use of crops is crucial for designing efficient irrigation systems, planning crop patterns, and estimating water requirements for irrigation projects.
• Reservoir operations: Consumptive use estimates are used to determine the amount of water that should be released from reservoirs for irrigation purposes, considering variations in seasons (e.g., Kharif vs. Rabi).

Relationship between ET and Consumptive Use

• Potential evapotranspiration: The concept of potential evapotranspiration incorporates consumptive use, as it considers the water lost through evapotranspiration, which cannot be reused or recovered.
• Plant water consumption: Consumptive use specifically accounts for the water consumed by plants through transpiration and evaporation from the soil.
• Definition of ET: ET can be defined as the total amount of water used by various systems, including plants, the atmosphere, and the soil, encompassing both evaporation and transpiration processes.