Weather Station Siting
Temperature is the driving factor in most phenological models, and proper measurement is critical for both development and use of the models. In addition to selecting accurate sensors, they should be mounted at an appropriate height and properly shielded from short-wave radiation (double shielding is best). Choosing small sensors that respond rapidly, protecting electronic leads, and ventilation (in areas with little wind) can improve accuracy of the temperature measurements. Data should be collected at a height that is typical of other weather stations in the area where the model will be used. Generally, agricultural weather stations collect temperature data at 1.5 to 2.0 m height and weather services tend to measure at 10.0 m height. For phenological models of natural vegetation, it is best to site the weather station in a similar environment without irrigation. However, when the models are used for irrigated crops, the stations should be sited over an irrigated grass surface to avoid temperature fluctuations due to intermittent rainfall at the measurement site. Strong temperature gradients can occur near large water bodies (e.g., the ocean or large lakes) and in hilly or mountainous regions where sunlight is blocked during part of the day. In such regions, more weather stations are needed to better characterize microclimate differences. However, even when the temperature data are accurately determined, inaccuracies in model predictions can occur because it is plant temperature rather than air temperature that truly drives the phenological development. Although little or no literature on the topic exists, perhaps using vapor pressure deficits to estimate plant from air temperature could improve models and make them more universally applicable.
Key wordsTemperature Measurement Standard surface Heat units Sensors
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