Evaluation of Dew Point Temperature as an Indicator of Aridity for Weather Collection Sites in Arizona

Integral to every farm management scheme is reliable weather data. These data become even more important in irrigated agriculture where daily fluctuations in temperature, solar radiation and relative humidity can have even a greater impact on scheduling the next irrigation. However, in collecting these weather parameters, one must be cognizant of the location where the weather data are collected. In Arizona, the AZMET network consists of 25 weather stations located throughout the state's agricultural regions collecting hourly data on temperature, solar radiation, relative humidity and wind. These data are used for a variety of purposes, including the computation of reference evapotranspiration (ETo) for use with irrigation scheduling. In order to properly compute ETo, the weather station must be placed in a well-irrigated site with sufficient fetch. To assure that the station is collecting reliable data, it has been suggested that a comparison between dew point temperature and minimum temperature be done. If the minimum temperature does not approach the dew point temperature (± 3°C), the site may be too arid, and the data should then be adjusted. However, in Arizona, with its natural occurring aridity, this criterion may not be valid since even under the most ideal conditions, the minimum temperature is well above the dew point temperature. In this paper, we exam the use of this criterion for Central Arizona.