How do the Qin Mountains divide the climate and geography of Shaanxi?

The Qin Mountains serve as a major environmental divide in China, separating Shaanxi province into two distinct climatic and geographical regions.12

Climatic Divide

The mountains act as a barrier that creates sharply differentiated climates:1
* South of the Mountains: This region experiences a subtropical climate characterized by hot, moist conditions. It features mean January temperatures between 37 and 39 °F (3 to 4 °C) and a long growing season of 260 to 280 days.1
* North of the Mountains: The Wei River valley and the Loess Plateau are significantly drier and colder. The Wei River valley has average winter temperatures near 32 °F (0 °C) and a shorter growing season of approximately 240 days, while the northern plateau becomes progressively colder and drier, with annual precipitation dropping to as low as 10 inches (250 mm).1

Geographical Divide

Structurally, the Qin Mountains form a massive, continuous barrier that separates the drainage systems of the province. To the south, the region drains into the Han River, a tributary of the Yangtze River, while to the north, the landscape is dominated by the Wei River valley and the northern upland plateau, which drain toward the Huang He.2