This document provides a summary of a lecture on the CLIMWAT and CROPWAT models. It discusses key concepts like reference evapotranspiration, effective rainfall, soil moisture, percolation, and irrigation efficiency. It then explains how CLIMWAT is used to provide climatic data for CROPWAT, which calculates crop water requirements and irrigation schedules. Examples are provided on using CROPWAT to determine crop water requirement, irrigation requirement, and field water supply for maize grown on 1 hectare of land. The importance of these models and improving irrigation practices is also discussed.
1. Lecture
on
CLIMWAT and CROPWAT model
Date: 9th August, 2018
at
ADRI, Patna
Er. Pawan Jeet
Scientist (LWME)
Division of Land and Water Management
ICAR-Research Complex for Eastern Region, Patna
2. ?
• Weather and Climate
• Irrigation and drainage
• Infiltration and percolation
• Precipitation and rainfall
• Potential ET and Reference ET
• Irrigation efficiency and water use efficiency
5. Input
• Irrigation: artificial application of water to soil for proper plant growth and
crop production (Israelsen, 1950)
• Irrigation efficiency: volume of water required for consumptive use by the
crop for its growth to the volume of water delivered from the source
• Irrigation efficiency
Irrigation system performance
Uniformity of water application
Response of crop to irrigation
7. Irrigation system performance
• Conveyance efficiency
Ec = (Vf / Vt) x 100
• Application efficiency
Ea = (Vs / Vf) x 100
• Storage efficiency
Es = [Vs / (Vfc – Va)] x 100
Where
Vf = Volume of irrigation water that reaches the farm or field
Vt = Volume of irrigation of water diverted from the water source
Vs = Volume of irrigation water stored in the root zone
Vfc = Volume capacity at field capacity in the crop root zone
Va = Volume of water in the root zone prior to an irrigation event
8. Cont…
• Scheme irrigation efficiency
• Overall irrigation efficiency
Eo = (Ec x Ea x Es ) x100
• Effective irrigation efficiency
Ee = [Eo + (FR) x (1 - Ea)] x100
Where
FR = fraction of surface runoff , seepage, and deep percolation that is recovered
9. Crop response to irrigation
• Crop water use efficiency
CWUE = Yg / ET
• Transpiration ratio (dry matter basis)
TR = ET / Yg
• Irrigation water use efficiency
IWUE = Yg / IR
Where
Yg = Economic yield
ET = crop water use
IR = irrigation water applied
10. Questions
A stream of 140lps was diverted from a canal and 110 lps were delivered to the field. An
area of 1.65 ha was irrigated in eight hours. The effective depth of root zone was 1.85
m. The runoff loss in the field was 435 m3. Available moisture holding capacity of the
soil is 20 cm/m depth of soil.
Determine the water conveyance efficiency, water application efficiency, water
storage efficiency and irrigation was started at a moisture extraction level of 50 percent
of the available moisture.
11. Solution
• Water conveyance efficiency, Ec = 100 x (Vf/Vd) = 100 x (110/140) = 78.5%
• Water application efficiency, Ea = 100(Vs/Vf)
Water delivered to the field = (110 x 8 x 3600) / 1000 = 3168 m3
Water stored in the root zone = 3168 – 435 = 2733m3
= 100 x (2733 x / 3168) = 86.26%
• Water storage efficiency, Es= 100 x (Vs/Vrz)
Water holding capacity of the root zone = 20 x 1.85 = 37 cm
Moisture required in the root zone = [37 – (37 x 50)/100] x 1.65 x 10,000
= 3052.5 m3
= 96.3%
13. Reasons for poor irrigation efficiency
• Non-stop flow of water to the field when the
amount of water needed has been delivered
• Absence of volumetric supply of water from the
water source to the field
• Non measurable soil moisture level at the time of
irrigation
14. Cont…
• Improper field levelling which cause poor water
distribution across the field
• Excessive slopes which cause high runoff losses
• Application of water not based on intake
characteristics of the soil
15. Improving irrigation efficiency
• Less stress on water resources, less losses of water
and nutrients to groundwater and surface water
resources
• Minimise irrigation inputs while continuing to
improve production and overall profits
• Allow a greater area to be irrigated with a given
volume of water
16. Cont…
• Modernization of Irrigation Projects
• Promotion of Efficient Irrigation Practices
• Promotion of Micro‐Irrigation Systems
19. Soil moisture
• Water contained in the vadose zone of subsurface
• Major component of soil hydrology that influences the exchange of heat and
moisture between the atmosphere and land surface
• Forecasts of runoff, flood, groundwater recharge and evapotranspiration
20. Applications of soil moisture
Soil
Moisture
Drought
monitoring
Climate
science
Flood
forecasting
Groundwater
recharge
Land
Atmosphere
processes
Ecological
status
Agronomy
21. Soil moisture
measuring
equipment's
Thermostat weight
method
Measure the electrical resistance
Hydrogen atoms that
changes with time
Changes in frequency of
signals due to the
dielectric properties of
the soil
Changes in the
dielectric properties of
the soil at microwave
frequencies
Soil moisture tension
23. Questions
Following data given below
Crop grown: Sorghum
Length of total growing season: Base period = 120 days
ETo = 6.0 mm/day
Kc = 0.78
Calculate ET crop.
24. ET Measurement
Evaporation
• U.S. Weather Bureau Class A Pan Evaporimeter
• ISI Standard Pan
• Sunken Evaporation Pan
• USGS Floating Pan
• Piche Evaporimeter
Lake Evaporation = Pan Coefficient x Pan Evaporation, or
ETo = Epan x Kpan
25. Questions
Following data are given below
Type of pan: Class A evaporation pan
Water depth in pan on day 1 = 150 mm
Water depth in pan on day 2 = 144 mm
Rainfall (during 24 hours) = 0 mm
K pan = 0.75
Calculate ETo.
27. Measurement of ET
• Thornthwaite
• Blaney-Criddle, FAO-24
• Hargreaves
• Christiansen-Hargreaves Pan Evaporation
• FAO-24 Pan Evaporation
• Penman FAO-24
• Penman-Monteith
• Radiation Method
Model
• CROPWAT
28. Penman Monteith equation
Where,
Lv = Volumetric latent heat of vaporization (Lv = 2453 MJ m−3)
ETo = Water volume evapotranspired or reference ET (mm s−1)
Δ = Rate of change of saturation specific humidity with air
temperature (Pa K−1)
Rn = Net irradiance (W m−2)
G = Ground heat flux (W m−2)
cp = Specific heat capacity of air (J kg−1 K−1)
ρa = dry air density (kg m−3)
δe = vapor pressure deficit, or specific humidity (Pa)
ga = Conductivity of air, atmospheric conductance (m s−1)
gs = Conductivity of stoma, surface conductance (m s−1)
γ = Psychrometric constant (γ ≈ 66 Pa K−1)
29. CLIMWAT
• Climatic database to be used in combination with the computer
program CROPWAT.
• Used to calculate crop water requirements, irrigation supply
and irrigation scheduling for various crops for a range of
climatological stations worldwide.
• CROPWAT requires local climatic data, but if these are not
available the software can use a representative station from
the CLIMWAT database.
30. Conte…
Long-term monthly data of seven climatic parameters
• Mean daily maximum temperature (°C)
• Mean daily minimum temperature (°C)
• Mean relative humidity (%)
• Mean wind speed (km/day)
• Mean sunshine (hours per day)
• Mean solar radiation (MJ/m2/day)
• Monthly rainfall (mm/month)
• Monthly effective rainfall (mm/month)
32. Weather observation networks in India
• Automatic Weather station : 675
• Automatic rain gauge : 1289
• Agro-met Unit : 130
IMD data availability
• Rainfall
• Temperature (Min/Max)
• Humidity
• Radiation
• Wind speed
• Evaporation
33. CROPWAT
• Crop water requirements and irrigation requirements based on soil,
climate and crop data
• Allows the development of irrigation schedules for different
management conditions and the calculation of scheme water supply
for varying crop patterns.
• can also be used to evaluate farmers’ irrigation practices and to
estimate crop performance under both rainfed and irrigated conditions.
34. Importance
• Monthly, decade and daily input of climatic data for calculation of
reference evapotranspiration (ETo)
• Possibility to estimate climatic data in the absence of measured
values
• Decade and daily calculation of crop water requirements based on
updated calculation algorithms including adjustment of crop-
coefficient values
35. Conti…
• Calculation of crop water requirements and irrigation scheduling for
paddy & upland rice, using a newly developed procedure to calculate
water requirements including the land preparation period
• Interactive user adjustable irrigation schedules
• Daily soil water balance output tables
• Easy saving and retrieval of sessions and of user-defined irrigation
schedules
• Graphical presentations of input data, crop water requirements and
irrigation schedules
46. Problems
Calculate field water supply, when following data is given
Crop: Maize
Cultivated area = 1 ha
Plant coverage: 100%
Reference ET = 7.216 mm/day
Average crop coefficient (Crop Kc) = 1.20
Effective rainfall = 2 mm
Irrigation efficiency = 70%
Crop Water Requirement (CWR) = ?
Irrigation Requirement = ?
Field Water Supply for one hectare = ?
47. Solution
Crop Water Requirement (CWR) = Reference ET x Crop Kc
= 7.216 x 1.20 = 8.659 mm/day
Irrigation Requirement (NIR) = CWR – Effective rainfall
= 8.659 - 2 = 6.659 mm/day
Field Water Supply/ha = (Area converge x IR)/ irrigation efficiency
= 1 x 6.659 x 1.428
= 95.07 m3/day
48. References
• FAO 56: "Crop Evapotranspiration - Guidelines for computing crop
water requirements”
• FAO 33: "Yield response to water“
49. The success of any Irrigation Technology
needs people
Who design & build it
Who live it
Sleep it
Dream it
Believe it
and build great future plans for it
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