Climatic characteristics of the Yellow River Basin

The Yellow River basin has a vast territory, numerous mountains, great disparity in height difference between east and west, and great differences in landforms in different regions. Because the basin is located in the mid-latitude zone, the situation affected by atmospheric circulation and monsoon circulation is more complicated. Therefore, the climate in different areas of the basin is significantly different, and the annual and seasonal changes of climate elements are great. The basin climate has the following main characteristics.

First, abundant sunshine and strong solar radiation.

The sunshine conditions in the Yellow River Basin are abundant in China, and the annual sunshine hours generally reach 2000 ~ 3300 hours. The annual sunshine percentage is mostly between 50% and 75%; The sunshine is the most abundant, second only to the Qaidam Basin, but generally about L times more than the vast area of the Yangtze River basin south of the Yellow River.

The total solar radiation in the Yellow River basin is moderate in China, with the area north of 37 north latitude and the plateau area west of103 east longitude between 130 ~ 160 kcal/cm2. Most of the rest areas are 1 10 ~ 130 kcal/cm2. Although it is not as strong as the southwest, especially the Qinghai-Tibet Plateau, it is stronger than the northeast and south of the Yellow River in general, and it is a strong radiation area in East China.

Second, there are large seasonal differences and wide temperature differences.

There are great seasonal differences in the Yellow River Basin, and the source area above jiuzhi county in Qinghai Province is "winter all year round". From Jiuzhi to Lanzhou and the middle and upper reaches of Weihe River, "winter is no longer than summer, and spring and autumn are connected"; The interval from Lanzhou to Longmen is "long in winter (six or seven months) and short in summer (one or two months)"; The remaining basins are characterized by "Leng Xia fever in winter and distinct seasons".

The disparity in temperature difference is a major feature of the climate in the Yellow River Basin. Generally speaking, with the three steps of the terrain, from west to east, the east-west gradient of temperature is obviously greater than the north-south gradient. The lowest center of the annual average temperature of about -4℃ is located at the northern foot of Bayan Kara, Heyuan, and the extreme lowest temperature in the basin appears at the station along the Yellow River in Heyuan, with a record of -53.0℃( 1978 1.2). The high value area of annual average temperature 12- 14℃ is located in Shandong province in the lower reaches of the Yellow River, and the extreme maximum temperature in the basin appeared at Yichuan Station in Luoyang, Henan Province, with a value of 44.2 C (1June 20, 966).

The annual temperature in the Yellow River basin varies greatly, and the general trend is that the area north of 370 north latitude is between 365,438+0 ~ 37℃, and the area south of 370 north latitude is mostly between 265,438+0 ~ 365,438+0℃.

The daily temperature range in the Yellow River basin is also relatively large, especially in the high latitudes in the middle and upper reaches. The daily temperature range of each season in the whole year is 13 ~ 16.5℃, which is in the national high value area or the second high value area.

Third, the precipitation is concentrated and unevenly distributed, which changes greatly during the year.

The annual precipitation in most areas of the basin is between 200 and 650 mm, and the middle, upper, south and downstream areas are all above 650 mm. Especially on the northern slope of the Qinling Mountains, which is greatly influenced by the topography in the south, the precipitation can generally reach 700 ~ 1000 mm, while it is less than 150 mm in some inland areas such as northwest Ningxia and Inner Mongolia. The distribution of precipitation is uneven, and the rainfall ratio between north and south is greater than 5, which is beyond the reach of other rivers in China.

It is dry in winter and dry in spring, rainy in summer and autumn, and the precipitation from June to September accounts for about 70% of the whole year. The precipitation from July to August in midsummer can account for more than 40% of the total precipitation in the whole year. The interannual variation of precipitation in the basin is also very different. The ratio of the maximum value to the minimum value of annual precipitation is about 1.7 ~ 7.5, and the coefficient of variation Cv varies between 0. 15 ~ 0.4.

Fourth, the humidity is small and the evaporation is large.

The middle and upper reaches of the Yellow River are areas with relatively low humidity in China, such as areas above Wubao, where the average water vapor pressure is less than 8 hectopascals and the relative humidity is below 60%. Especially in the upper reaches of Ningxia, Inner Mongolia and above Longyangxia, the annual average water vapor pressure is less than 600 Pa. The relative humidity between Lanzhou and Shizuishan is less than 50%.

The evaporation capacity of the Yellow River basin is very strong, and the annual evaporation capacity is 1 100 mm. The upper reaches of Gansu, Ningxia and the central and western Inner Mongolia are the regions with the largest annual evaporation capacity in China, and the maximum annual evaporation capacity can exceed 2500 mm.

5. Hail, sandstorm and sand blowing.

Hail is one of the main disastrous weather in the Yellow River Basin. According to statistics, the number of hail days in Lanzhou, Inner Mongolia and other places in the upper reaches of the Yellow River is more than 2 days, including more than 5 days in the west of east longitude 1000, especially in Maqu and the upper reaches of Datong River 15 ~ 25 days, which has become the area with the most hail in the Yellow River basin and also the hail concentration area in China.

Dust storms and sand blowing are mainly caused by strong winds, which are closely related to local (or nearby) geological conditions and vegetation conditions. According to statistics, in Ningxia, Inner Mongolia and northern Shaanxi, the average number of windy days for many years is more than 30 days, and there are Tengger Desert, Wulanbuhe Desert and Mu Us Desert in the region. Most sandstorm days in the whole year are above 10, and sand blowing days are above 20 days. In some years, sandstorms can last for 30 ~ 50 days, and the days of sand blowing exceed 50 days. In addition, in the upper reaches of Fenhe River and along the Yellow River below Xiaolangdi, there are also areas where the annual sandstorm or sand blowing days exceed 20 days, which is mainly related to the large-scale existence of beaches in the Yellow River.

Sixth, the frost-free period is short.

The first frost days in the Yellow River basin begin gradually from north to south and from west to east, and the mountainous areas at the same latitude are earlier than the plains, valleys and deserts. For example, the average first frost day above Tangnaihai in the upper reaches of the Yellow River is in the middle and late August, while the middle and lower reaches of the Yellow River are generally in the middle and early June10; The rest of the basin is in September. The distribution characteristics of the last frost day in the basin are just the opposite to the first frost day. The lower reaches of the Yellow River are earlier, with an average of late March, and the upper reaches of Tangnaihai are later than early and middle August, and the rest areas are in between.

It can be seen that the frost-free period of the Yellow River basin is short, even in the plain area of the lower Yellow River, the frost-free period is only about 200 days; The average time in the upper reaches of the Yangtze River is less than 20 days, so it can be said that there is frost all year round. The rest of the basin is in between.