First of all, the most basic condition for becoming a major grain producing area is not water resources, but topography. The reason why the north can become the main grain producing area is mainly because the cultivated land in the north is relatively wide, and the cultivated land is mainly plain terrain, and the north has inherent advantages, such as the North China Plain, the Northeast Plain, the Guanzhong Plain, the Huanghuai Plain, the Jiaolai Plain and other medium and large plains are basically located in the north.

Although there are many plains in the south, such as the middle and lower reaches of the Yangtze River, Chengdu Plain and Xun Yu Plain. The area of these plains cannot be compared with that of the northern plains.

For example, the plain in the middle and lower reaches of the Yangtze River is the largest plain in the south. In fact, the plain in the middle and lower reaches of the Yangtze River is the floorboard of six unconnected plains, the largest of which is Jianghan Plain, with an area of 46,000 square kilometers, but the area of Jianghan Plain is not as large as that of Guanzhong Plain in the north, and it can only be considered as medium-sized.

To give another obvious example, there are four plains in Fujian, namely Putian Plain, Zhangzhou Plain, Fuzhou Plain and Quanzhou Plain, the largest of which is Zhangzhou Plain, with an area of 566 square kilometers. However, the northward movement of Zhangzhou Plain may not be a plain, but only a "corridor" or a "basin". Therefore, before the absolute terrain area is established, water resources cannot be the decisive factor of the main grain producing areas.

In addition, another reason why the north can become the main grain producing area is also related to the planting attributes. The cultivated land culture in the north is more inclined to "dry farming", and the south is more inclined to paddy fields, that is, rice cultivation. In contrast, the crops planted in dry land are more diverse, such as wheat, corn, peanuts, soybeans, sorghum, millet, etc., which can be widely planted in the north and get a good harvest.

The grain in the south is mainly rice. Although the yield per mu of rice is getting higher and higher, it is definitely not as good as the sum of grain in the north. If potatoes and sweet potatoes are counted as food, the yield data in the south is even worse than that in the north.

Of course, the current lack of water resources in the north will really affect the growth of grain, especially in Hebei and Henan areas of the North China Plain. In recent years, the rainfall is really small, and the grain yield per mu has dropped. However, the northern plains are too widely distributed, and the saying that "the east is not bright and the west is not bright" is untenable. Hebei and Henan are dry, and the three plains of Shandong and Northeast China also belong to the north. Therefore, the grain yield per mu caused by drought in some parts of North China has little effect on the total grain output in the whole North. To sum up, no matter in the past, present or future, the north will always be the main grain producing area in China.