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Recent Impacts of Climatic Extreme Events on Everyday Food in Japan:
The Need for an Adaptation Strategy for Climate Change

Shunji Ohta
Professor, Faculty of Human Sciences, Waseda University

It is understood readily that agricultural crops are essential to our everyday food and that agricultural production can be determined easily by climatic conditions. Because of this, many readers would have great interest in future climate warming and the recent climatic phenomena that will directly affect food production. However, I would like first to draw the reader’s attention to the widespread misuse of the term “climatic anomalies.” In fact, this term refers in meteorology to the peculiar climatic phenomena with low frequency, which occur approximately once every 30 years in any given region. Thus, in general, most of the climatic phenomena that are thought of as “anomalies” are more accurately described as “extreme events.”

Crops and livestock suffer from heat stroke just as humans do

Among the extreme events occurring recently in Japan, what you imagine first may be the heatwaves, the scorching hot summers of recent years. Human health is damaged directly through heat exhaustion, heat illness, and other conditions, due in particular to the extreme daytime heat. Livestock and crops likewise suffer from heat stroke, and these symptoms are referred to by agricultural meteorology and plant physiology as “high temperature injury.” It has been found that high temperature injury is caused by a significant increase in the temperature from nighttime to dawn (in other words, the daily minimum temperature), as well as high daytime temperatures (in other words, the daily maximum temperature). Such increases in temperature in summer lead to flowering injury, and budding injury also occurs in spring, since plants need to be exposed to low temperatures for a certain period in winter.

In addition, high temperature injury also affected the yield of crops. Plant production occurs through photosynthesis, and a part of this is used for the plant’s own respiration, so the net primary production (NPP) is the value that subtracts plant respiration from plant production. Although photosynthesis is maximized at a certain optimum temperature, the amount of respiration increases exponentially with an increase in temperature, so beyond a certain temperature, the NPP falls dramatically. It is therefore a mistake to think that productivity will increase due to global warming making the climate warmer. Furthermore, a high temperature injury does not just reduce the production, but it also affects the quality of crops. For example, if rice crops are exposed to high temperatures during the first two weeks or so after an ear emergence, the rice grain turns white and becomes immature rice kernels with white portions. During the record-breaking hot summer of 2010, the average temperature across Japan reached 28 to 29 degrees Celsius, causing a mass occurrence of milky white rice kernels, and significantly reducing the proportion of first grade rice kernel produced in all regions. In the past, the warm region agriculture in the Kyushu region produced a very high proportion of first grade rice kernel, while the proportion in the Tohoku region and Hokkaido was low due to cold damage, but recently the situation has been completely reversed, and the quality of the rice crop in Northern Japan has risen while that in Western Japan has fallen (Figure 1).

Figure 1. Temporal change in the proportion of first grade rice kernel in Northern Japan and Western Japan (created based on Ministry of Agriculture, Forestry and Fisheries data).

The main cause of the high temperatures in the summer of 2010 was the La Niña phenomenon, in which the sea temperature in the Eastern Pacific Ocean dropped, causing the energy balance between the atmosphere and the oceans to differ greatly from that in ordinary years (called a “normal” year in meteorology). This was also the reason why the winter of 2009 to 2010 was harsh in Japan and its vicinity. The yields of autumn-sown wheat in Hokkaido decreased approximately 30 to 40% due to the low temperatures in the early spring (causing the increased number of ears) and the shortened ripening period in the hot summer (causing the reduced kernel weight). Moreover, coloration damages also occurred in fruits such as Satsuma mandarins and apples and so on. This resembles sunburn in people, and reduced the economic value of the fruit. Other effects of the high temperatures of 2010 were the reduction in milk production and changes in the weight of a livestock, both of which were conspicuous in comparison with ordinary years.

Increases in sea surface temperature lead to moving fishery resources and increasing flood damages

We do not obtain our food only from the terrestrial ecosystem but also from the aquatic ecosystem, including the seas. In recent years, the sea surface temperature (SST) around the Japanese archipelago has been on a long-term rising trend, which is particularly marked in the central Japan Sea region, at an increase of 1.7 degrees Celsius. The atmosphere in the Hokuriku region is unstable during fall and winter, with many thunderstorms and a great deal of snowfall. This is because the SST of the Japan Sea is higher than the atmospheric temperature of the land at the same period, and cold air converges above the sea with a very high water temperature. Since SSTs that were already high become higher than in ordinary years, warm water fish like Japanese Spanish mackerel in the scombrid family, which used to be caught in the East China Sea, have become plentiful in the Japan Sea since the latter half of the 1990s. As a result, in recent years, Wakasa Bay has become Japan’s biggest fishery of Japanese Spanish mackerel. In contrast, catches of Japanese flying squid have been greatly reduced in the Japan Sea coastal regions of Honshu.

On the other hand, in the past few years, damage resulting from the torrential rainfall (heavy intense rainfall) has frequently occurred in the summer in Japan, often lasting several days. Crop damage due to heavy intense rainfall cause even greater reduction in the yield for the afflicted region than that caused by temperature, putting the livelihoods of people working in agriculture at risk. The cause of this heavy intense rainfall is also the increase in SST. In the summers of 2012 and 2013, the SST of the seas around the Japanese archipelago reached over 28 degrees Celsius, which is almost the highest value seen on any of the world’s sea surfaces, and is almost the same as the tropical sea temperatures in the Indian Ocean, etc. The cause for the increase in SST in recent years has not yet been fully clarified, but it could be due to the increase in temperature of the atmosphere on a global scale being absorbed by the world’s seas and oceans, which have a high heat capacity (the major factor in the recent rise in sea levels is the heat expansion caused by this, not the melting of polar ice).

This warm, moist air due to high sea temperatures causes a local heavy rainfall, when concentrated in a specific location. In general, most climatic events that occur in Japan, since it is located mid-latitude, can be explained by the meandering of the westerlies that move periodically from west to east (Figure 2). For some reason, the meandering undulation of the westerlies has become too large, and when an indent is formed, the pressure distribution becomes fixed and isolated from the main flow of the westerlies (known as “blocking” in meteorology). In the period from late July to August of this year, due to the formation of an indent in the westerlies in the vicinity of the Korean Peninsula, the front was blocked and became stuck. Then, the warm air containing evaporated seawater around the Japanese archipelago pushed towards the low pressure areas on the Japan Sea side of Western Japan and the Tohoku region again and again. We call this “Wet tongue” in meteorology, and as a result, the rainfall occurred lasting several days in same local areas (Figure 3).

Figure 2. The meandering course of the westerlies (meandering mainly over the Arctic Pole, having been formed from the two atmospheric flows of the subtropical jet from the equator and the polar jet from the pole).

Figure 3. Distribution pattern of pressure in summer around the Japanese archipelago.

The heavy intense rainfall during the summers of 2012 and 2013 occurred due to the mechanism described above. We can explain the heavy intense rainfall in this year that occurred in seemingly unrelated areas such as Yamaguchi, Shimane, Tottori, Ishikawa, Niigata, Aichi and Akita prefectures, among others, in the same way. Because the heavy intense rainfall occurred over a relatively limited local area, the reduced yield and damage to quality of crops had a relatively small impact on Japan’s overall food production. However, the yield and quality of crops of open-culture were depressed, so the temporary supply shortages and the price increases of foods were caused.

The need for an adaptation strategy for each region

Above, I have described the extreme events and changes in agriculture and fisheries in Japan in the past few years, but in the long-term, the negative effects are predicted to be even worse, and we expect those industries to become more vulnerable. Leaving aside whether or not this is being caused by the global warming due to human activities, the effects of climate change are already occurring at high frequency around us now. We have no choice but to accept this fact.

The methods of reducing our vulnerability relating to these climatic extreme events are adaptation and mitigation strategies. As scientists, we can predict the vulnerability to climate changes, with some uncertainties, on each regional scale. Then, citizens and policy-makers must accept these results and think about what is to be done to adapt to these undesired phenomena. From fiscal 2010, the Ministry of Education, Culture, Sports, Science and Technology launched the Research Program on Climate Change Adaptation (RECCA). The scientific results of this program will be important in considering the future of food policy in Japan as well. It is not a matter of simply trying to stop climate change or extreme events by creating a low carbon society, but there is a need to accept the vulnerability of our agriculture and fisheries and decide on policies and strategies to adapt to the future climate change at the earliest possible opportunity at both the national and local authority level.

Shunji Ohta
Professor, Faculty of Human Sciences, Waseda University

Born in Shinkawa-cho (now known as Kiyosu city), Aichi Prefecture. Graduated from Department of Basic Human Sciences, School of Human Sciences, Waseda University in 1991. Completed the doctoral program in the Department of Life Sciences, Graduate School of Human Sciences, Waseda University in 1996. Ph.D. in Human Sciences. Served as Assistant at the School of Human Sciences, Waseda University from 1996, Associate Professor at the Department of Ecosocial System Engineering, at Yamanashi University from 1999, before becoming Associate Professor and then Professor, his current position, at the School of Human Sciences, Waseda University in 2001.

[Major published works related to this article]
Edited by S. Ohta et al. (2010). Edited the section on “Food,” in the Dictionary of the Body and Temperature [Karada to Ondo no Jiten] (Edited by S. Ohta et al., Asakura Publishing, 2010), 640 pages.
Ohta S (2009). Food Production in the Context of Changing Climate: Global Environmental Information in the 21st Century [Henka suru Kiko to Shokuryo Seisan—21 Seiki no Chikyu Kankyo Joho], (Corona Publishing), 213 pages.
Ohta S. & Kimura A. (2009). “The effects of plant growth on the temperature of paddy waters.” Journal of Agricultural Meteorology 65: 167–178.
Ohta S. & Kimura A. (2007). “Impacts of climate changes on the temperature of paddy waters and suitable land for rice cultivation in Japan. Agricultural and Forest Meteorology 147: 186–198.