Agroclimatology: Atmospheric Moisture

• Course focuses on agroclimatology principles by Prof. Marco Bindi.
• Agroclimatology covers weather, climate, meteorology, and agricultural meteorology.
• It also includes atmospheric composition, climate factors, climate classification, and climate systems.
• Agro-climatological parameters include radiation, temperature, air humidity, soil humidity, precipitation, and wind.
• Agro-climatological parameters can be measured using instruments, stations, and satellites.
• Climate and crops are related through climate types, vegetation, altitude, latitude, and agro-climatological parameters.
• The course addresses climate change, its impacts on crops, and adaptation/mitigation strategies.
• Agroclimatology tools by Dr.ssa Camilla Dibari are part of the curriculum.

Atmospheric Moisture

• Atmospheric moisture or air humidity refers to the amount of water vapor in the air in gas form.
• Water cycle interactions: evaporation and transpiration
• Energy balance involves radiation interacting with water vapor.
• Plant diseases can be influenced by leaf wetness.
• The maximum amount of water vapor in the air depends on air temperature.
• Water vapor content decreases with height because the water source is on Earth’s surface.
• Water vapor is more than 1% near the Earth and almost 0% beyond 8 km height in the atmosphere.
• Cloud formation is limited to a maximum height of 8 to 10 kilometers.
• Absolute humidity: the weight of water vapor per unit volume expressed in grams per cubic meter (g m-3).
• Vapor pressure: the pressure due to water vapor's weight on a surface unit area (Pa, hPa, or KPa).
• Relative humidity: the ratio of actual water vapor to the maximum water vapor capacity at a given temperature (percentage).
• Vapor Pressure Deficit is calculated the difference between saturated vapor pressure and effective pressure.
• Dew point is the temperature at which air must cool to reach condensation.
• Relative humidity is the accepted way to express air humidity for agro-climatological applications.
• Relative humidity has a negative correlation with maximum temperature.
• Hair hygrometers are mostly used in greenhouses and mist chambers.
• The sensor in hair hygrometers is human hair, which expands/contracts with humidity.
• Capacitive humidity sensors measure humidity's effect on a polymer's or metal oxide's dielectric constant.
• Resistive humidity sensors measure the change in a material's electrical resistance caused by humidity.
• Thermal conductivity humidity sensors measures the change in air's thermal conductivity related to humidity.
• Thermal conductivity sensors measure absolute humidity.
• Psychrometers consist of two thermometers: a dry-bulb and a wet-bulb
• The wet-bulb thermometer is kept moist with distilled water, which lowers the temperature as water evaporates from the wick.
• Calculation of relative humidity uses dry and wet bulb temperatures.

Soil Humidity

• Soil humidity is expressed as the percentage of water in a unit mass or volume of soil.
• Also expressed as water potential, indicating the pressure with which the soil retains water (KPa).
• Saturation (Sa), field capacity (FC), and wilting point (WP) are critical moisture thresholds for plants.
• Threshold percentages depend on soil texture like the sand, clay and silt.
• Saturation is 0 KPa or 0 pF, field capacity is -100 KPa or 2 pF, and wilting point is -1600 KPa or 4.2 pF
• Soil humidity can be determined through gravimetric or time domain reflectrometry (TDR) analysis.
• Gravimetric water content is measured by weighing, drying at 105°C for 24 hrs, and reweighing a soil sample.
• TDR principles measure the propagation time of an electromagnetic pulse along measuring pins in the sample.
• The propagation time depends on the humidity content of the medium.