1. Principles of Agroclimatology
Course Lecturers: Olaoye, Gbadebo Office Location: – Professorial Suite Olaniyan, J.O. Office Location: – Department of Agronomy Building Ahamafule, H. A.

2. General Introduction.
Terminologies relating to climate, factors of climate and relevance of climate to general agriculture.
Elements of climate
General Influence of weather variables –temperature, heat, relative humidity, wind, cloud and atmospheric pressure on crops. Evaporation and evapotranspiration.

3. Rain formation and rainfall pattern
Process of rain formation. Process of rain formation –convection, cyclonic and orographic. Factors affecting rainfall distribution and amount. Importance of rainfall on vegetation and distribution of crops.
Weather equipment and maintenance of standard meteorological stations
Weather station. Components of weather station. Instruments for measuring temperatures, sunshine, relative humidity, wind direction and speed, atmospheric pressure and solar radiation.

4. Methods for estimating evaporation and evapotranspiration
Use of evaporating pans, Atmometers, Sunking Tank, mass transport method, water balance method design and use of lysimeters
Climate and Agriculture
Nature of the tropical climate and crop distribution. Implications on the type of cash and arable crops that could be cultivated.
Impact of climate change especially global warming on general agriculture and by implication human nutritional status and health.

5. Climatic variables and crop productivity I Sun Energy
Influence of sun’s energy, air temperature on crop productivity. Components of the atmospheric air-ammonia, carbon dioxide
Climatic variables and crop productivity II- Soil moisture
Soil moisture properties. Soil surface temperature on crop growth and performances. Plant water status

6. Estimating effects of climatic variables on crop growth and productivity
Equipment used in measurement of crop response to differences in climatic variables. Measurement of CO2 exchange between atmosphere and vegetation, carbon dioxide flush, loss of ammonia, combined effects of carbon dioxide and air temperature.
Cropping patterns in relation climate
Sole cropping versus crop mixture. Different intercropping patterns – mixed cropping, alley cropping relay cropping, strip cropping and terracing.

7. Irrigation in a sustainable agriculture
Irrigation as source of water in dry land agriculture. Irrigation requirements. Meteorological parameters associated with irrigation agriculture.
Problems associated with irrigation
Effects of erosion, leaching, water logging on crop productivity, human lives and community health.
General revision

8. Lecture 1-General Introduction
Agroclimatology
Term describes the interrelationship between elements of climate and agriculture
Branch of science which deals with the study of climate and effects on crop and livestock productivity
A special discipline of agriculture that
relates the influence of climatic factors to agriculture,
measurements of climatic factors and
how they can be used to enhance crop and livestock productivity
Climate is the average of all weather conditions of a given place over a period of time
Weather is the state of the atmosphere at a given point in time and at a given location
Weather and climate occupy central position within the broad spectrum of environmental science and consequently in the field of agriculture
In tropical Africa, weather also determines the type of vegetation, the type of crops that could be grown and also the types of livestock that can be raised.

9. Relevance of Climate to Agriculture
It is the basis for the distinction between regions (Temperate versus Tropical zones
It influences life and development of organisms
It has significant effect on general agriculture including
livestock production,
nature of vegetation,
soil characteristics,
types of crops that could be cultivated in a particular area and
farming systems in a given locality.

11. lecture 2: Elements of Climate
Temperature, wind, pressure, rainfall, etc. are collectively referred to as elements of climate
Temperature
Defined as the heat condition of a given place.
Two major aspects of temperature are insolation and heating/cooling effects
Directly related to amount of insolation received in an area.
Every crop has a range of temperature (minimum, maximum and optimum) within which it could survive and not only become productive but gives it best.
Similarly, livestock has a range of temperature for optimal performance.
Most crops give their best within the temperature range of 15oC and 32oC.

12. Temperature affects crops by influencing
Differences exist among crops and livestock in their tolerance to temperatures (high or low). For example, millet (Sorghum bicolor) tolerates high temperature better than maize (Zea mays L).
Temperature affects crops by influencing
the actual amount of vapour in any medium thereby deciding its moisture carrying capacity and
affecting evaporation and evapo-transpiration rates, consequently, condensation to form relative humidity (RH).
High temperatures may cause
pollen abortion in maize,
boll shedding in cotton (Gossipium spp),
premature fruit drop in tomatoes (Lycopersicon esculentus) and orange (Citrus spp),
drop in egg production in poultry birds, etc.

13. Insolation
Defined as the sun’s energy which is converted into heat at the earth’s surface i.e. solar radiation).
It is the ultimate source of terrestrial and atmospheric energy.
Approximately 45% of incoming insoaltion reaches the earth surface while the rest is scattered, absorbed or partly reflected by various components (water droplets, cloud, dust and various gases present in the atmosphere.
Solar radiation is the source of energy utilized by plants in photosynthesis and chief determinant of dry matter production in plants.
Cereal crop yields are usually superior in the northern Nigeria to the south due to better insolation (less cloudy sky) and late cropping season yields better than early season crop yields in the south for the same reason.
High temperature in conjunction with low relative humidity ensures better livestock productivity in the northern Nigeria relative to the south.

14. Total sun energy approaching the earth’s surface and the proportion that actually reaches the earth’s surface.

15. Factors influencing temperature of a place
These are latitude/altitude, ocean current/distance from the sea, wind, cloud cover, relative humidity and day length among others.
Latitude/Altitude
At high altitude, air contains very little vapour or dust and heat from earth’s surface rapidly escapes so that air remains cold.
Latitude/Altitude also affects diurnal range of temperature especially in the arid areas where there is marked differences between day (very hot) and night (very cold) temperatures.
Ocean currents/Distance from the sea
Cold currents often raise or lower the temperatures of land surfaces. Warm currents carry tropical warmth from the pole into high altitudes.
Warm currents (between Latitudes 0o and 40o) on eastern sides of continents, raise costal temperatures.

16. Winds
On-shore winds of tropical latitudes modify the temperatures of coastal regions owing to its blowing over cooler surfaces
Cloud cover
Clouds reduce the amount of solar radiation reaching the earth’s surface and the amount of radiation leaving the earth the earth’s surface.
Heavy cloud cover of equatorial regions is responsible for day temperatures exceeding 30oC (86oF).
Absence of cloud cover in the desert regions results in excessive high day and low night temperatures.

17. Relative Humidity (RH)
It is the amount of water vapour in the air which is directly related to the atmospheric temperature.
RH has a considerable effect on the moisture requirements of crops.
Lower relative humidity (RH) at a given temperature encourages fast absorption of transpired water through evaporation in the leaves.
Day Length
Very important to growth and development of crop plants, having a pronounced effects on flowering and seed germination.
Certain cowpea (Vigna unguiculata L Walp) are long day plants (>14 hours). Most rice (Oryza sativa) cultivars are generally short day plants (<10 hours). Maize is a day neutral crop (10-14hours).

18. Wind
Strong wind such as hurricanes, cyclones, etc., may cause soil erosion and stem breakage resulting in severe crop losses especially in the cereals (maize, sorghum, millet, sugarcane).
Strong winds may also increase the rate of evapo-transpiration in the leaf surfaces of plants, thus affecting moisture balance in crops.
Moderate winds may
promote photosynthetic rate in plants and
enhance pollination in wind pollinated crops (maize).
Atmospheric Pressure
The weight of the air which it exerts on the atmosphere is referred to as atmospheric pressure. Atmospheric pressure depends upon three elements: altitude, temperature and rotation of the earth.

19. Rain
Rainfall (amount and distribution) is the most important climatic factor influencing agriculture in the tropics.
It determines to a large extent,
agricultural potential of an area,
crop and livestock types,
farming systems and timing of farm operations.
Rainfall distribution also determines the number of cropping seasons (two in the south and one in the north).

20. Clouds Made of water droplets or ice particles.
Mist and fogs are low level clouds.
When air is cooled, some of its water may condense into tiny droplets of water.
Shape, height and movement of clouds indicate the type of weather which is likely to occur.
Dew point temperature is the temperature at which the change of water droplets or ice particles to form cloud.

21. Evaporation and Evapotranspiration
Evaporation (E) is the amount of water moved from the leaf surfaces of plants.
Physical process by which liquid or solid is transferred to gaseous state.
E Occurs from the immediate surfaces of water bodies (oceans, lakes, rivers), from soils and wet vegetation.
Process from the plant surfaces is through the plant → root hairs→ vascular tissue →leaves or other organs → plant into the surrounding air → stomata or cuticular surfaces and the process is therefore referred to as Transpiration.
Soil evaporation and plant transpiration occur simultaneously.

22. E rate is affected by wind velocity which absorbs any available moisture.
Evapotranspiration (ET) is a combination of evaporation of water remaining on the surfaces of vegetation after precipitation and transpiration (water lost from plant’s surface).
ET is used to describe total process of water transfer into the atmosphere from vegetated land.
Potential evaporation (PE) occurs when the soil moisture is greater than a critical value above which evaporation takes place.
Actual evaporation (AE) occurs when soil moisture is less than the critical value resulting in the rate of evaporation itself far below PE (i.e. soil moisture is less than critical value)

23. Lecture 3: Rainfall and Vegetation Pattern
Process of Rain formation
Air Rises→ Air Cools→ Air Condenses→ Clouds Form and →Precipitation Occurs.
Under certain conditions, water vapour (in form of a gas) becomes tiny droplets of water in the lower layer of the atmosphere.
When droplets become too heavy (in the presence of condensation) to remain suspended in air, may then fall as rain (Tropical regions) or snow (Temperate regions).
They may initially appear as cloud, mist, fog, hail, dew or rain referred to as Precipitation.

24. Three conditions for precipitation
Air must be saturated.
Air must contain small particles of matter (dusts) around which droplets are formed.
Air must be cooled below its dew point which is achieved either through rising of air or passing of air over a cold surface.

26. Types of rains Convectional Rainfall Relief Rainfall and
Frontal (Cyclonic or Depression) Rainfall
The three types of rainfall: Relief (left), Frontal (middle) and Convectional (right).

27. Conventional rainfall
Convectional rain is caused by convection where the surface layer of the atmosphere is heated causing the moisture laden air to rise.
Forms due to heating of the ground by the sun.
The condition of rising currents of warm air separated by more wide-spread areas of slowly sinking air is referred to as convection.

28. Air (close to the ground) is heated, becomes lighter and begins to rise → then cools forming (water vapour) → condenses back to water droplets→ forms clouds which when it grow bigger→ rain under the influence of gravity.
Common in areas where ground is heated by the hot sun (for example the Tropics).
Convectional rain can also be found year round in regions near the equator.

29. Relief Rainfall
Forms where moist air is forced to rise over mountains or hills.
Presence of hills or mountains leads to the warm air rising.
The winds pick up moisture from the sea as they pass over it, and this makes the air moist.

30. As the air rises to pass over the higher land, it cools and the water vapour condenses, forming clouds.
The droplets then fall as rain, sleet, hail, or snow, depending on the atmospheric conditions.

31. Frontal (Cyclonic or Depression) Rainfall
Frontal rainfall occurs where warm air meets cold air.
The warm air is lighter than cold air and it is therefore forced to rise above it.
As the air rises it begins to cool and condense.
As the water vapour condenses back to water droplets, clouds are formed. As the clouds grow bigger it starts to rain.

32. This rain is caused by depressions
Cyclonic rain originates where warm tropical air meets cold polar air. The warm air overrides the cold air.
When contrasting air masses make contact, an abrupt zone or boundary is formed.
This boundary is called a Front and is accompanied by rather abrupt changes in temperature, pressure and humidity.
When a mass of warm air moves into a region of cold air, the warm air overrides the cold air mass, forcing the cold air to retreat.
This situation is called a Warm Front, which is characterized by several days of rain.

33. Nigeria vegetation Forests (where there is significant tree cover),
Savannahs (insignificant tree cover, with grasses and flowers located between trees)
Montane land (mainly found in the mountains near the Cameroonian border).
Forest and Savannah zones are each divided into three parts.

34. Peculiarities of forest zone
Some of the forest zone's most southerly portion, especially around the Niger River and Cross River deltas, is mangrove swamp.
North of this is fresh water swamp, containing different vegetation from the salt water mangrove swamps, and
north of that is rain forest.

35. Peculiarities of the savanna zone
Guinea forest-savanna mosaic, made up of plains of tall grass which are interrupted by trees, the most common across the country;
Sudan savannah, similar but with shorter grasses and shorter trees;
and Sahel savannah patches of grass and sand, found in the northeast.

36. Types of Cropping Season
Nigeria, like the rest of West Africa and other tropical lands, has only two seasons
Dry season and
Rainy season.
The dry season is accompanied by a dust laden air mass from the Sahara Desert, locally known as Harmattan, or by its main name, The Tropical Continental (CT) air mass.
The rainy season is heavily influenced by an air mass originating from the South Atlantic Ocean, locally known as the south west wind, or by its main name, The Tropical Maritime (MT) air mass.

37. Lecture 4: Weather Measuring Equipment
Rain Gauge – Amount of precipitation
Thermometers – Air temperature
Hydrometer – Moisture content or humidity of the air
Wind vane – Direction of the wind
Anemometer- Wind speed or Velocity
Barometer - atmosphere air pressure
Evaporating pans –Evaporation and
Lysimeters - Evapotranspiration

38. Weather Station
Weather is "the state of the atmosphere at a given time and place, with respect to variables such as temperature, moisture, wind velocity, and barometric pressure."
Weather Station:
A weather station is a facility (either on land or sea) with instruments and equipment for observing atmospheric conditions to provide information
for weather forecasts and
study the weather and climate.
The measurements taken include temperature, barometric pressure, humidity, wind speed, wind direction and precipitation amounts.

39. Modern weather station (Mauritius Sugar Research Institute)
Old (Greenveson weather station)

40. Components of a Weather Station
Thermometers for measuring air temperature,
Hydrometer for measuring relative humidity,
Barometer detects atmospheric pressure,
Anemometer for measuring wind speed and
Gauges measure rain and snow.

41. Sophisticated weather station equipment.

42. Front (a) and back view (b) of typical weather station containing sunshine recorder, wind vane and other accessories for recording climatic data at CMMYT station, Kenya.

43. Measures the amount of rainfall at a given time interval
Measurement of Rainfall-Rain Gauge
Measures the amount of rainfall at a given time interval
Can be any container (Fig. 1), with marked measurements (in, cm or mm).
It is important to use the correct rain gauge, as evaporation can be a factor.
Most standard rain gauges have a wide funnel leading into the cylinder and are calibrated so that one-tenth of a mm of rain measures 1mm when it collects inside.

44. In the more modern era, a common rain gauge is called the tipping bucket type.
Contains a pair of small receiving funnels alternate in the collection of the rains.
When one fills up with water, it tips, spills out, and the other comes into place to do the collecting.
The funnels tip each time rainfall amounts to .01 inches, which triggers a signal that is transmitted and recorded.

45. Measurement of Air Temperature-Thermometers
Thermometers measure air temperature by using materials that change in some way when they are heated or cooled.
More specifically, the device measures the air’s heat content.
Temperatures are measured in degrees Celsius or degrees Fahrenheit, depending on location.
There is a combination of maximum and minimum thermometers
Thermometers used for keeping weather records are usually enclosed within a specified shelter (Right) called the Stevenson’s Screen so as to minimize environmental effects, such as topography, or shade and shadows which can skew thermometer readings.

46. Thermometers used for keeping weather records are usually enclosed within a specified shelter (Right) called the Stevenson’s Screen.
The purpose is to minimize environmental effects, such as topography, or shade and shadows which can skew thermometer readings.

47. Maximum and Minimum Thermometer
Consists of a U shaped glass tube with two separate temperature scales set along each arm of the U
The bulbs are hidden by a plastic housing.
One housing is for recording max tempt and the other for min tempt.
Left-hand (minimum arm) full of alcohol measures the tempt by expansion and contraction of the liquid.
Maximum and Minimum Thermometer

48. Right-hand (maximum arm) contains alcohol and a bubble of low-pressure gas or alcohol vapour.
This accommodates expansion in the other bulb and allows the train of alcohol and mercury to move in the U-shaped tube as the temperature changes.
A metal in the bend of U section contains mercury which is liquid at normal temperatures. Which is pushed around the tube by the thermal expansion and contraction of the alcohol in the first bulb as it responds to the external temperature.

49. Note:
At the end of every reading, the thermometer must be reset by moving the markers to the top of the mercury, usually by hand using a small magnet to slide them along the tube.
As the temperature varies, the markers will remain in their positions unless the temperature becomes higher (for maximum) or lower (for minimum) than already recorded, in which case the relevant marker is pushed further.
Typically the thermometer is reset every 24 hours to measure the diurnal temperature variation

50. Six's thermometer
Commonly known as a maximum-minimum, minimum-maximum, maxima-minima or minima-maxima thermometer
Records maximum and minimum temperatures reached over a period of time, for example 24 hours.
Records extremes of temperature at a location, for instance in meteorology and horticulture.
The thermometer indicates the current temperature as well as the highest and lowest temperatures since last reset.
Six’s Thermometer

51. Measurement of Soil Temperature-Soil Thermometer
Soil temperatures are usually measured at various depths – 5cm, 10cm, 20cm, 50cm and 100cm.
Soil Thermometer is used for this purpose.
It is a mercurial thermometer with bulbs embedded in paraffin wax.
The thermometer is suspended in steel tubes and inserted into the soil at various depths.

52. Relative Humidity Definitions
The moisture content or the humidity of air or any gas
Measure of comfort at different temperatures or expression of how the temperature feels. .
Saturation point of water vapour in the air.
Often recorded as the “amount as a percentage of that required to saturate the air completely” (BBC, 2008).
More humidity, like in Lagos (Nigeria) which is very close to the sea, equals more discomfort.

53. Hygrometer:-
Instrument used to measure the moisture content or relative humidity of air. A Psychrometer is a form of hygrometer which uses the evaporative cooling of a thermometer bulb.
Dial Precision Thermohygrometer: Provides accurate humidity and temperature readings. Upper scale shows humidity while lower scale shows temperature

54. Wind (Weather) Vane:
Measures direction of wind using arrows that point out the direction of motion as it spins and points in the direction from which the wind is coming
The arrow points to the direction the wind is blowing from indicating where the wind is blowing from.
Note: (i) Knowing the direction of the wind is an important part of predicting weather because wind brings us our weather.
(ii) Wind direction indicates where the wind is blowing from. For example, a west wind is blowing from the west. (iii) To use a wind vane, you must know where north, south, east and west are.

55. Different types of wind vane indicating the direction of the wind for predicting weather.

56. Anemometer
Measures wind speed or velocity (i.e. the strength of the air’s motion).
It is an instrument with three or four small hollow metal hemispheres set so that they catch the wind and revolve about a vertical rod
Several cups catch the wind, spinning them around a vertical pole and the wind speed is calculated by the number of revolutions per minute.
An electrical device records the revolutions of the cups and calculates the wind velocity.

57. A typical anemometer (Left) and Combination of anemometer with other components -wind vane, sunshine recorder(Right).

58. Barometer:
Measures atmospheric air pressure by weighing the amount of air in a specific place
Can be considered a weather predictor, rising and falling with advancing storms.
Falling barometer indicates an advancing storm or bad weather while a rising barometer indicates improving weather.
Note: Pressure tendency can forecast short term changes in the weather. For example, high or rising pressure is an indication of clear cool weather while low or falling pressure suggests warmer more unsettled weather.

59. Different types of Aneroid Barometers
Different types of Aneroid Barometers. A typical aneroid barometer (Left), old aneroid barometer (Centre) and modern aneroid barometer (Right).

60. Mercury Barometers
A very early and traditional method for measuring air pressure is to observe a column of mercury within a vertical glass tube.
Barometer works by balancing the weight of mercury in the glass tube against the atmospheric pressure just like a set of scales –where mercury is lower than the atmospheric pressure, the mercury level in the glass tube rises and where weight of mercury is more than the atmospheric pressure, the mercury level falls.
Atmospheric pressure is basically the weight of air in the atmosphere above the reservoir. So the level of mercury continues to change until the weight of mercury in the glass tube is exactly equal to the weight of air above the reservoir.

61. Two types of Mercury Barometer.

62. Digital Barometers
Compact size, contemporary styling, special features, and affordability make digital barometers a great choice for many.
Eco-celli Barometers
No mercury!
It uses a patented combination of gas and silicon based fluid to replace the mercury without any loss of the accuracy you expect with a mercury barometer.
Digital Graphing Barometer

63. Torricelli Mercury Barometer
A glass tube from which the air has been removed is inserted into a dish of mercury.
The air pressing down on the mercury in the dish forces some of the mercury up into the glass tube.
The height that the mercury rises in the glass tube is directly related to the atmospheric pressure.
This pressure is usually measured in inches of mercury but can be converted to millibars. For example, a measurement of inches of mercury is equivalent to millibars.

64. Torricelli Mercury Barometer

65. Measurement of Radiation
Net Radiometers – Measure only net radiation. Pyranometers- Measure the total short wave radiation from the sky incident on a horizontal surface at the ground. Pyrheliometers – Measure solar intensity or the direct beam solar radiation (Q) at normal incidence. These are the most accurate of all radiation instruments. Pyrradiometers – Measure only the albedo of the surface Pyrgeometers – Measure infrared long wave radiation from the earth’s surface or the atmosphere depending upon whether it is downward facing or upward facing. Albedometers – Measure only the albedo of the surface

66. Pyranometer
Campbell-Stokes Sunshine Recorder

67. Estimating Evaporation and Evapotranspiration
Evaporation and Evapotranspiration are interwoven and cannot be easily separated
Evaporation is measured by evaporimeters including class A pan and Piche
evaporimeter
Evapotranspiration can be estimated using hydrological and micro-meteorological methods using lysimeters (i.e. the weighing lysimeter and the drainage lysimeter).

68. Piche Evaporimeter
Most common instrument for measuring evaporation in West Africa.
Consists of graduated measuring cylindrical tube (22.5cm long; internal diameter of 11mm and external diameter of 14mm), with closed and an open ends.
Open end of the tube has wetted surface (a filter paper disc) held by a spring fitted with a disc and collar. Water is supplied to the paper at the open end by a wick inking it to a small water container normally graduated in millimeters.
Evaporation from the instrument is the difference between the readings of the container at the beginning and end of the period.
It is not reliable because it is assumed to measure the drying power of air rather than the amount of water lost by evaporation to the atmosphere.

69. An evaporation pan is used to hold water during observations for the determination of the quantity of evaporation at a given location.
Measurement from Pan evaporation combines or integrates the effects of several climatic variables-temperature, humidity, rainfall, drought dispersion, solar radiation, and wind.
Note:
Evaporation is greatest on hot, windy, dry, sunny days; but greatly reduced when clouds block the sun and when air is cool, calm, and humid.
Pan evaporation measurements enable farmers and ranchers to understand how much water their crops will need.

70. Diagrammatic representation of Class A pan
Class A evaporation pan

71. Sunken Colorado pan
It is another form of evaporating pan with surface area 4m2 and 0.6m deep.
As the name suggests, it is buried in the ground to within about 5cm (2 in.) of its rim.
Usually filled with water up to a depth of 52.5cm2 and set in the ground such that 7.5cm of the tank protrude above the ground surface.

72. Limitations of sunken Colorado pan include
After rainfall, amount of rainfall collected in the drum is subtracted from the initial measurement.
Limitations of sunken Colorado pan include
loss through splashing especially at high incidence under high rainfall and
leakages which is often too difficult to detect

73. Raised Tank
Another type of pan is the raised tank which is a rectangular tank of volume (915mm x 1270mm x 432mm deep).
The depth of the water in the tank is about 350mm.
A wooden platform is used to raise the tank so that the water surface is about 457mm above the ground.
Diagrammatic representation of Raised Tank

74. Atmometers:
Scientific instrument for measuring evaporation rate from a wet surface to the atmosphere.
Usually made with a porous flat plate-like object (e.g. a filter paper) which can draw water from an easily measurable source (e.g. a graduated cylinder) via a wick.
As water evaporates from the surface, more water is drawn from the source through the wick by capillary action to replace the water lost by evaporation.

75. By periodic measurements of the quantity of water remaining in the graduated cylinder, a rate of evaporation can be established.
Also, using the surface area of the plate, we can establish a rate of evaporation per unit area.
Evaporating surfaces is either coloured black (to absorb incident radiation) or white (to reflect incident radiation).
Difference in water evaporated between black and white units can be used as indication of intensity of radiation.
Major limitation is their sensitivity to changes in windiness than to changes in radiation.

76. Measurement of Evapotranspiration- Lysimeter
A lysimeter is used to measure the amount of actual evapotranspiration (which is released by plants, usually crops or trees).
By recording the amount of precipitation that an area receives and the amount lost through the soil, the amount of water lost to evapotranspiration can be calculated.
Early devices, called pan lysimeters, collect soil water as it percolates down via gravity through saturated soils.
Modern automatic instrumentation is relatively straightforward to calculate evaporation and is done so by professional hydrologists and others  

77. A lysimeter is most accurate when vegetation is grown in a large soil tank which allows the rainfall input and water lost through the soil to be easily calculated.
The amount of water lost by evapotranspiration can be worked out by calculating the difference between the weight before and after the precipitation input.
Lysimeters can be expensive and are a poor representation of conditions outside of a laboratory especially with for trees,
For farm crops, it can represent field conditions well since it is done outside the laboratory.

78. Lysimeter Scheme

79. Maintenance of Meteorological Station
Maintain a clear viewing area around the station ( i.e. Buildings should not be located close to the meteorological station.
Remove big trees around the station.
Keep the grass low at all times.
Evaporating pans and tanks should be protected from animals and birds
Replace malfunctioning equipment promptly.