What is the cause of drought in the Southwest? Environmental lesson useful, urgent!! 5

The first is the plateau thermal factor of the Qinghai-Tibet Plateau. Sichuan Province is greatly affected by the "roof of the world", the Qinghai-Tibet Plateau had little snow last winter, and the plateau thermal factors are good, which affects the drought in the province.

The second is the impact of El Niño. Under this influence, the heat flow in the surface of the Pacific Ocean travels eastward, carrying away tropical water vapor, resulting in more precipitation in eastern China. In contrast, tropical water vapour decreased, and water vapour from the south to the southwest also decreased.

Third, the timing of cold air has not been mastered. Although there have been several times of cold air affecting China this winter, most of the cold air has begun to move eastward in the north, directly "slipping" past the edge of Sichuan Province. Coupled with the relationship between the Qinling Mountains, if the cold air is not "strong" enough to climb the mountain, it will still not be able to affect the basin.

Even though sometimes cold air enters the basin and forms the first condition for rainfall: convective weather, the second condition for rainfall, water vapor, which is not abundant, cannot form precipitation. "It's a process that requires cooperation. ”

According to experts, this drought lasted almost 200 days, which is a very long time, and there are very few droughts that exceed 200 days in history. "At present, from the autumn and winter of 1998 to the spring of 1999, there were more than 210 days of widespread drought in the northern winter wheat region, which is the longest in history. Of course, the three-year drought in the early '60s also had a long period of continuous drought of nearly 200 days, but the two aforementioned droughts may have had a much larger impact if we look at the scope alone.

Recently, China's southwestern region is still in the midst of a drought that has not been seen in a century, and the continuous sunny, hot and rainy weather has led to the continuous aggravation of the drought situation in the five provinces, autonomous regions, and municipalities of Yunnan, Guizhou, Sichuan, Chongqing, and Guangxi.

The first is the influence of plateau thermal factors on the Qinghai-Tibet Plateau. Other provinces in southwest China are greatly affected by the "roof of the world", the Qinghai-Tibet Plateau last winter had less snow, the plateau thermal conditions are good, resulting in the weakening of the Indo-Burma trough, the weak South Asian monsoon, the water vapor transported to the southwest of China is not abundant, coupled with the cold air from the north to the south to the east and north, resulting in drought in the southwest region.

The second is the impact of El Niño. Under this influence, the sea surface temperature in the eastern equatorial Pacific Ocean is warmer, the subtropical high is stronger overall, and the water vapor carried by the East Asian monsoon meets the cold air from the north to the south, resulting in more precipitation in the eastern part of China and frequent snowfall in the north. On the contrary, the southwest region of China is dominated by downdrafts, and there are often sunny and sunny weather.

The third is that there is no cold air opportunity. Although there have been several cold air impacts on our country this winter, most of the cold air has started to move eastward in the north. With warm air forms the first conditions for rainfall:

Convective weather. However, if the second condition for the formation of rainfall, "water vapor", is not abundant, it still cannot form good precipitation.

Sea and land location, monsoon factors: Southwest China is Chinese mainland, and the summer monsoon from the Pacific Ocean has brought less rainfall when it arrives. The same is true for the summer monsoon from the Indian Ocean, which is blocked by the Himalayas and Hengduan Mountains.

In addition, summer monsoon activity is erratic, and sometimes drought occurs.

Topographic factors: There are mountains and mountains near the southwest region, and it is in the first and second steps of our country, and the altitude is relatively high.

[Climatic reasons].

High temperature and lack of rain is the direct cause of drought in southwest China, and the air circulation situation shows that the southern branch trough is weak in winter, and the warm and humid airflow from the southwest of the Indian Ocean is relatively weak, resulting in insufficient water vapor.

Human causes] Cutting down of original ecological forests and planting rubber forests and eucalyptus forests in southwest provinces led to the reduction of water level and the weakening of water culvert capacity. Forcing other species to decline, ultimately causing subversive damage to the ecology. (Typical destruction of the environment for the sake of immediate interests, leaving a legacy for future generations!) ）