Factors Affecting Consumptive Use of Water

•Evaporation from soil•Mean monthly temperature•Wind velocity at particular height•Relative humidity at the surface and the overlying layer

• Day light hours• Cropping pattern and season• Irrigation practices• Depth of irrigation• Soil type and topography• Average rainfall in the locality

DIRECT MEASUREMENT OF CONSUMPTIVE USE

Tank and Lysimeters Experiments

Lysimeters can be grouped into three categories:

•Nonweighing, constant water table type for use where a high water table normally exists.

• Nonweighing, percolation type often used in areas of high precipitation.• Weighing types, which provide the most accurate data for short time periods.

Soil Moisture Depletion

This method is usually suitable for areas where soil is fairly uniform and depth to ground water is such that it will not influence soil moisture fluctuation within the root zone.

Integration MethodIt is the summation of the products of unit consumptive use for each crop times its area, plus the unit consumptive use of native vegetation times its area, plus water surface evaporation times water surface area, plus evaporation from bare land times its area.

Inflow-Outflow for Large Areas

Formula:

U= (I+P) + (Gs-Ge) –R

Where:U - Valley consumptive useI - Water that flows into the valley during a

12-month yearP - Yearly precipitation on the valley floor.Gs - Water in the ground storage at the

beginning of the year.Ge - Water in the ground storage at the end

of the year.R - Yearly outflow

Energy Balance and Heat and Mass Transfer

It can be used for hourly values during daylight hours but accurate nighttime values are difficult to obtain.

IN DIRECT MEASUREMENT OF CONSUMPTIVE USE

Penman Method

This method uses evaporation data from free water surface and their corrective coefficients. Penman method shows that consumptive use is inseparably connected to incoming solar energy.

Thornthwaite Method

This method is frequently used in regions of semi-humid climate and is usually connected with the calculation of hydro balance.

Lowry-Johnson Method

This method applies to a valley, not to an individual farm.It assumes a linear relationship between effective heat and consumptive use.

Blaney-Craddle Method

A simplified formula using temperature and daytime hours is used for the arid regions. This approach uses a consumptive use factor obtained by multiplying the mean monthly temperature and daytime hours of the year.

Shaumyan’s Method

Shaumyan tackled the relation of water consumption in relation to crop yield.

Sharov’s Method

Sharov provided insights on evapotranspiration by observing water consumption through the evaporation from the soil and plants transpiration from physical standpoint.

Bouchet’s Method

Bouchet uses evaporation value from Piche’s evaporimeter as the basis for calculating evapotranspiration with provision for correction to accommodate climatic factor.