Application of Probabilistic Risk Assessment to the Chalky Rice Grain Issue in Japan

Abstract

In recent years, extreme weather events have become more frequent, and there are concerns about the increase of chalky rice grains. Therefore, it is important to understand the frequency and severity of high-temperature injuries to rice grains occurring nationwide in Japan. Thus, the objective of this research was to analyze the hazard of high temperature through a probabilistic method using big weather data and to assess the risk of chalky rice grain. In this research, we analyzed air temperature data from approximately 800 stations of the AMeDAS (Automated Meteorological Data Acquisition System) in Japan and checked the chronological changes. To assess the risk of chalky rice grain, the Probabilistic Risk Assessment (PRA) method was applied and the risk for each of the 20 years from 1980 to 1999 and from 2000 to 2019 was compared. Chalky rice grains, which reduce rice quality, increase when the average temperature exceeds 26 °C during the first 20 days after the heading date of rice. A comparison of the areas with air temperatures exceeding 26 °C at least once per three years (33.3 %) between the past and the recent 20 years shows that the risk of high temperatures has increased in the inland areas of the southern Tohoku region and the southern part of Ibaraki Prefecture. Subsequently, a multiple regression model was applied to identify the factors affecting high temperature risk. The 20-day averaged daily mean temperature, which has a probability of 33.3 %, was set as the dependent variable, and longitude, altitude, and urban area ratio were set as explanatory variables. As a result, regions located further north experience greater temperature increases due to climate change, and regions with higher urban rates also experience greater temperature increases due to anthropogenic effects.