Development of daily mean air temperature data with 50-m resolution for an information system identifying the suitable planting period for Yamadanishiki sake rice

Degradation of the quality of Yamadanishiki sake rice has become more evident in the last 15 years, which is partly attributable to high temperature damage to the rice during heading. In response, an information system has been developed to determine the suitable planting period for this rice variety. A key input to this system is daily mean air temperature data at fine spatial resolution, and here an estimation method to calculate such data on a 50-m grid is presented. This database contains daily mean air temperature for 244 days in target regions from April through November over 15 years (1996-2010). The database is obtained by applying a method whose essence is to convert air temperature to potential temperature and build estimation models of the potential temperature difference between an estimation site and existing observation site. The potential temperature differences are partitioned into two components: a "standard site component (Tssc)" and "estimation site component (Tesc)." Estimation models for Tssc and Tesc are developed using a radiative cooling scale, i.e., the difference of potential temperature between an upper level and ground level. Daily air temperature at each output grid was estimated to have a root mean square error of 0.5 degree C. Our method is able to acquire precise daily air temperature for past, present and future at the existing observation site, without newly costs for installation and maintenance of regular observing instruments.