In addition to the requirements of a variety of crops, the temperature of the duration and accumulated temperature, in its reproductive growth period also requires certain high temperature conditions, especially in hot crops, especially the hottest month (July) average temperature as the crops required high temperature Value. China in addition to the size of the Northeast Xing'an Mountains, the Qinghai-Tibet Plateau and mountain areas, most of the country's hottest monthly average temperature above 20 ℃, can meet the general needs of crops. Rice growth period requires the hottest month average temperature of 20 ℃ or more, most parts of the country where the water can be irrigated rice. Cotton the hottest month average temperature 23 ~ 25 ℃ above, the temperature is not high can not bud, flowering, boll, boll opening. The hottest month on average temperature is lower than 11 ℃ region basically also can not cultivate farming area area at present.
China is located in the northern hemisphere in the mid-latitude, about 50 degrees across latitude, is located in the southeast of Eurasia, east of the Pacific, the northwest half of the high terrain, low southeast half, so the temperature has a larger seasonal change during the year.
The isothermal distribution of the isotherm is basically east-west, with the distribution density of the isotherm being the largest in the whole year, with an average difference of about 1.5 ℃ between each latitude. South of the Qinling Mountains and east of the Qinghai-Tibet Plateau, the average temperature in January is higher than 0 ℃, north of less than 0 ℃. Due to the influence of the northern continental air mass, so in January as the representative of the winter temperatures than the northern hemisphere are the same latitude regions are low.
July is the highest monthly average temperature in most parts of the month, when the impact of latitude on the temperature d istribution has been reduced to the minimum, the southeast half of the average north-south temperature difference of only about 0.3 ℃ each latitude. In addition to the Qinghai-Tibet Plateau and the Tianshan Mountains, the vast areas in July the average temperature is above 20 ℃.
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