In the case of complicated topography such as hilly mountainous areas and slopes, depending on the location of the farmland, the daily minimum temperature may be nearly 10°C lower than the value of the weather data provided for each 1km mesh. The National Agriculture and Food Research Organization (NARO) has developed a method that can estimate the daily minimum temperature with a 5m mesh, considering the movement of the cold air drainage that occurs with radiative cooling at night. In the future, this result is expected to contribute to the development and provision of accurate weather data for agricultural land located in places where cold air drainage is likely to occur due to complex topography such as slopes and hills and useful for frost damage prevention and growth prediction of crops.
Overview
The importance for weather information is increasing due to climate change and the accompanying frequent occurrence of extreme weather events. Especially, for local phenomena in farmlands, meteorological information with finer spatial resolution is desired. NARO is promoting the development of "Meteorological Grid Square Data", which provides weather data for each 1km mesh nationwide. However, it is known that the actual minimum temperature is lower than the minimum temperature estimated by "Meteorological Grid Square Data" especially in farmlands with complicated topography such as large elevation differences in narrow areas such as hilly and mountainous areas and this difference can be close to 10°C. This is because the ground cools down due to radiative cooling at night, the cooled air near the ground flows into the valleys of the topography, and the cold air accumulates in the depressions, increasing the temperature difference with the surroundings. In order to provide temperature information while considering the effects of cold air drainage, thermometers equipped with a ventilation device and a sunshade must be installed at intervals of several meters to several tens of meters to accurately measure the temperature . However, it is technically and economically difficult to realize.
Therefore, using two indices such as, the flow accumulation obtained from elevation data and the radiative cooling intensity obtained from the difference in temperature at two altitudes at representative points and by considering changes in cold air drainage, NARO has developed a method to correct the daily minimum temperature of "Meteorological Grid Square Data". In this method, by formulating a relationship between the minimum temperature measured at the site and the above two indices, the daily minimum temperature can be estimated with the same spatial resolution as the elevation data used. The elevation data used in this study (Digital elevation model provided by the Geospatial Information Authority of Japan) has a very fine resolution of 5m. Hence by using this method, users can accurately know the minimum temperature in their own fields. In addition, this method is practical because it can be used with simple temperature sensors (such as three-globe thermometers) and elevation data.
In the future, based on the results of this research, we will build a system that can predict the minimum temperature at a given location and date, which can provide accurate meteorological data. It is expected to be used for crop growth prediction and frost protection.
Publication
Kimura Kensuke, Maruyama Atsushi, Sasaki Kaori, Kudo Ken, Tanaka Eri, Fushimi Erina, Nakagawa Hiroshi, 2023, Fine-scale mapping of daily minimum temperature in a cropland with complex terrains through the combination of a cold flow accumulation model with inversion strength. Agricultural and Forest Meteorology, 329, https://doi.org/10.1016/j.agrformet.2022.109247
For Inquiries
Contact: http://www.naro.go.jp/english/inquiry/index.html
