Class A evaporation pan

Height 254 mm

Diameter 1026 mm.

Daily changes in the depth of water (Epan, mm/day) estimates the evaporative potential of the environment. High values of Epan will be observed on sunny, windy days with low atmospheric humidity. Water-use by plants (transpiration) will be similar to Epan if the plants are well watered (no water stress) and have a high leaf area index (Crop Factor).

Standard rain gauge

Height 400 mm;

Diameter 200 mm.

A graduated cylinder inside the collector gives a direct measure of rainfall since the last reading (mm/day). Non-standard instruments in non-standard locations give non-standard readings. Inexpensive plastic gauges attached to buildings or fence posts are widely used but may give an inaccurate estimate of rainfall.

Standard Stevenson screen with the front door pen.

The louvered enclosure allows free movement of air across the enclosed instruments while shielding them from direct sunlight and rainfall. Usual instruments enclosed include: Maximum and minimum thermometers (°C); current air temperature (°C); wet and dry bulb thermometers (°C); thermo-hygrograph to provide a continuous record of temperature (°C) and humidity (% of saturation). Instruments are read daily at 0900 hours and perhaps also at 1500 hours. In recent times data are collected electronically but the importance of screening and location of the sensors remains.