Abstract: Heilongjiang province, with an important responsibility for food security, is in the middle-high latitudes. Thermal resource is an important factor restricting agricultural production in the province. Meanwhile its climate warming has been significantly higher than the national average in the past 60 years. Changes in thermal time and thermal time zones play decisive roles in the distribution of agricultural varieties, the adjustment of agricultural planting structure, and the formation of output. Using daily and monthly average temperature data of 31 national meteorological stations in Heilongjiang province from 1961 to 2020 and “Grid dataset of monthly average surface temperature in mainland China revised based on the urbanization deviation”, changes of thermal time above 10℃ in Heilongjiang province before and after de-urbanization were analyzed. The results show that after removing the effects of urbanization, the linear change trend and rate of change tendency of thermal time from 1961 to 2020 have slowed down in Heilongjiang province. In the past 30 years during 1991 to 2020, the average thermal time generally decreased after de-urbanization. The increase thermal time caused by urbanization was below 100℃·d in most areas. The amount of Huma, Heihe, Shangzhi and Bei'an exceeds 100℃·d, and Sunwu exceeds 200℃·d. Five of six thermal time zones in Heilongjiang province were adjusted due to the removal of urbanization. The range of First Zone was greatly reduced, which led to a significant increase in Second Zone, and Third, Fourth, and Fifth Zones moved south.

Key words: Heilongjiang province, Thermal time above 10℃, Zone of thermal time, Urbanization, Comparative analysis