TOKYO >> Concerns over crop damage due to global warming have spurred the development of heat-resistant rice varieties around Japan.

While these varieties are grown in less than 10% of the total area cultivated for rice, since 2010 the hectarage has more than doubled.

Several of these varieties have received high marks in taste, and many believe they will only become more widespread going forward.

In late May, an agricultural corporation was planting a paddy in Satte, Saitama Prefecture, with the heat-resistant variety sainokizuna.

“It withstands hot weather and tastes good,” said company president Yoshitaka Funakawa.

Sainokizuna is a Saitama variety that was registered in 2014. Its brown rice tends to maintain high quality and harvest levels even in high temperatures. The Japan Grain Inspection Association gave it the highest grade — toku-A — in its 2017 taste ranking, the same grade as given to the popular koshihikari from Niigata Prefecture.

About 19,480 tons of sainokizuna were harvested in 2018, some 13% of the more than 150,000 tons of rice that was harvested in Saitama Prefecture that year.

Recent summers have been brutally hot, adversely affecting koshihikari, a common variety grown nationwide. If temperatures are high when the ears of rice emerge, quality degrades.

Sainokizuna, however, has greater capacity to evaporate moisture from pores in the surfaces of its leaves, lowering temperatures from the heat of vaporization.

In 2018, which saw “disaster-level heat,” just 21% of Saitama koshihikari rice was deemed grade-one — rice of the highest quality — compared to 84% for sainokizuna.

Tochiginohoshi, a Tochigi Prefecture variety that was registered in 2015, has received the toku-A grade three times, in 2015, 2017 and 2018. The percentage of grade-one rice in 2018’s 22,500-ton harvest was 98%. It was grown on 8% of the total hectarage in the prefecture, the third- biggest variety by area.

“The quality is good and harvests are big, so more farmers are growing it,” said an official at the Tochigi Prefectural Agricultural Experiment Station.

Natsukirari, an Aichi Prefecture variety that is said to taste similar to koshihikari, was registered in 2017 and is undergoing test cultivation.

According to a February 2018 report by the Environment Ministry and other groups, average temperatures in Japan have risen by more than 34 degrees in the last 100 years and are predicted to rise by as much as 41.7 degrees in the 21st century.

Rice harvests in the plains of the Kanto region and in the Hokuriku region and westward are expected to drop, fueling the push to develop heat-resistant varieties.

In 2010, these varieties were grown on about 37,700 hectares (about 93,160 acres), according to the Agriculture, Forestry and Fisheries Ministry. By 2017, growing area had increased to 93,800 hectares (about 231,785 acres). This accounts for about 7% of the 1.37 million hectares (nearly 3.4 million acres) cultivated for rice in 2017.