1, you can try to start from the perspective of disasters. It seems that there were many disasters in Japan in 2004, such as a typhoon and a Niigata earthquake (it is estimated that it is more likely to import more grain and agricultural products that are easy to store as emergency grain reserves). You have to look up the information yourself.

2. Compare the varieties exported to rural areas with the changes of export quantity in previous years. It is not easy to judge only from the total change at a certain time.

3. In addition, exchange rate changes and bilateral trade relations. It may all have an impact.

Personally, I think it is mainly disasters that may have more effects.