2020/12/10：Update. Added observation results until harvest season in 2020 captured by GCOM-C, Sentinel-2, Landsat-8 and ALOS-2.
Satellite imagery observed by ALOS-2 PALSAR-2 and GCOM-C operated by JAXA, Sentinel-2 by ESA, and Landsat-8 by NASA/USGS were used to assess the state of rice cultivation near Sacramento, California, USA. These observations show that the rice planting, heading and harvesting this year began earlier than the past two years in many regions, and rice planting area was larger than last year.
As for the timing of planting, effect of weather conditions is one reason. In addition, there is a possibility that high rice price caused by the COVID-19 related concerns over global rice supply through potential increases in demand, threats of export restrictions, and shortage of labor.
Global food supply in the best conditions is becoming a major challenge. COVID-19 has strained the food supply and demand balance by disrupting food supply chain systems, such as labor, logistics, trade/domestic policies, and market anxiety. In the case of rice production, COVID-19 contributed to concerns over global supply through potential increases in demand, threats of export restrictions, and farm labor concerns. These and other factors resulted in a reported high rice price and increase in global rice production.
For decades, satellite monitoring for global food supply has provided critical, independent, and objective indicators of major commodity supplies, and it has been continued during the COVID-19 pandemic. Satellite imagery is able to confirm planting progress in key rice producing areas. Satellite imagery are used to assess the state of planting near Sacramento, California, USA, using ALOS-2 PALSAR-2 and GCOM-C operated by JAXA, Sentinel-2 by ESA, and Landsat-8 by NASA/USGS. These satellites can capture rice phenology, when rice is planted, mature and harvested, through the observation of land surface conditions such as water inundation for planting and leaf area after emergence.
Satellite observations show that the rice planting and harvesting in this year began earlier than the past two years in many regions. In addition, the planting area was larger than last year. Early assessments of planting or harvesting progress allow agriculture markets to respond efficiently to supply disruptions due to natural (e.g. weather, pandemics) and man-made events (e.g. trade policy changes).
Satellite observations show that the rice planting in this year began earlier than last year (Figure 1). Observations by Synthetic Aperture Radar (ALOS-2) show the timing of paddy field flooding was earlier than last year in many areas (Figure 2).
Normalized Difference Vegetation Index (NDVI) is highly related with vegetation of the amount green leaves. So, higher value shows rice growing conditions with much green leaves. According to the time-series changes of NDVI observed by GCOM-C, Sentinel-2, and Landsat-8 optical satellites, the earlier increase of NDVI than in previous years indicates that the sowing period of the paddy rice began earlier. (Figures 3 and 4).
Also, the peaks of NDVI means that the amount of paddy rice leaves was at its maximum (heading period). The earlier peak of NDVI this year indicates that heading period was earlier than previous years. Similarly, the decrease of NDVI means that leaves turn yellow or red and leaf mass decreases due to harvesting. The earlier decrease of NDVI indicates that the harvest period of paddy rice was also earlier than previous years. The Foreign Food Supply and Demand Report (October 2020, in Japanese) published by the Ministry of Agriculture, Forestry and Fisheries of Japan also states "According to the U.S. Department of Agriculture, California's harvest progress was 90 percent, which is higher than the same period last year (77%). ", which is consistent with the tendency by satellite observations.
In addition, Rice planting area around Sacramento was estimated by machine learning technology, which is utilized for AI etc., using complex utilization of images from ALOS-2 (Rader) and Sentinel-2 (Optical) (Figure 5). Rice harvest in this year is expected to increase, because planted area has expanded in 2020 compared to 2019. The planted area in 2019 was 496,000 acres (official statistics by USDA). Furthermore, the planted area in 2020 estimated from ALOS-2 is 515,000 acres. This estimated area will be the second largest on record since 2014.