Geographical environment of Ningdu County
Ningdu County is located between 26 5' 18 "and 27 8' 13" north latitude and 115 4' 2 "east longitude. Mid-subtropical monsoon humid climate zone. The climate is mild, the four seasons are distinct, the sunshine is abundant, the rainfall is abundant, there is no severe cold in winter and the frost-free period is long, which is suitable for the normal growth of subtropical crops.
Four seasons change
In winter, from late November to early December, Ningdu is in the southeast of Mongolia cold high pressure, so it often blows north wind or northeast wind. During this period, there was a cold wave, accompanied by frost, snow and freezing weather. Normal years are: the previous winter was cold, sunny, frosty and dry; After winter, it is rainy and snowy, and the weather is cloudy and cold. As the saying goes, "39, 49, don't shoot when you meet." He also said: "Great cold, slight cold, dripping into a ball." From mid-January to mid-February, it is the coldest season of the year, and heavy snow and freezing rain mostly occur during this period.
in the middle and late March of spring, the intensity of cold high in Mongolia gradually weakened, while the subtropical high in the Pacific gradually approached the county, with the temperature rising and more rain, which is called "continuous spring rain" and "no sunny days in spring". However, the temperature in the early stage is still low, often influenced by strong cold air, and sometimes the weather is cold. As the saying goes, "The tiger froze to death in Qingming Grain Rain". In the later period, the air mass between the north and the south moves towards each other in the county. The precipitation is intense and concentrated, and there are often heavy rains, which make the river water level rise sharply and flash floods. This is the flood season in Ningdu, and there are often thunderstorms or hail.
Summer begins in late May, and enters midsummer after the flood season. Due to the control of the Pacific subtropical high, the weather is hot. Because it is located at the northern edge of high pressure, it often blows southerly or southwesterly winds. There is a saying that "there is a small south wind for 18 days." When the secondary high pressure is strengthened or weakened, it is easy to form hot thunderstorm weather. This kind of hot thunderstorm mostly occurs in the afternoon or evening, and its locality is obvious. There is a saying that "summer rain blocks the wall, but women don't shower their mothers". During this period, typhoons often affected the county, and precipitation, cooling, strong winds and heavy rains occurred.
Autumn comes in late September. After the summer monsoon weakens, but the temperature is still high, which is commonly known as "autumn tiger". However, the heat at this time is different from before. The so-called "White Dew and Autumn Equinox, cold at night and hot during the day". That is, although it is hot during the day, it turns cold at night and autumn is getting stronger. During this period, the ground to the middle and low altitude is controlled by cold high pressure, while the middle and high altitude is still affected by warm high pressure. From the ground to the high altitude, it is high pressure, and it is cold and warm, and the gas layer is stable, so it is not easy to form clouds and rain, and the weather is sunny in most years. In late autumn, there is "Xiaoyangchun" weather to promote the flowering of plants and even bear fruit.
Temperature and frost
Temperature The annual average temperature is between 14 and 19℃. The mountains in the north are low, and the hills and valleys in the south are high. Meijiang Valley and Gucun Basin in Huangshi and Laicun are two areas with high average temperature, above 19℃. The average annual temperature in Xiaotian and Langji in the north is only 14℃. Extreme temperatures are also high in the south and low in the north. The extreme maximum temperature has a small difference between north and south, while the extreme minimum temperature has a big difference.
The monthly average temperature is below 1℃ from December to February, with the lowest temperature in January. There were nine consecutive months from March, and the average temperature was above 1℃, with the highest temperature in July.
according to the county's stable passage of 1-2℃, the start and end dates with 8% guarantee rate: 1℃ first appeared on March 25th, and 2℃ finally appeared on September 28th, lasting 187 days, with a total accumulated temperature of 4723.5℃.
the annual precipitation is between 15 and 17 mm. Generally speaking, there are more in the north, less in the south, more in the east and less in the west.
the precipitation from April to June accounts for 4~7% of the annual precipitation, with a large proportion.
if it exceeds 3% of the average annual precipitation from April to June, it will be designated as a particularly heavy water year. Since 1939, 1944, 1948, 1954, 1959, 1962, and 1968 have been exceptionally heavy years of water. Major floods occurred in these years.
if it is lower than 3% of the average annual precipitation from April to June, it is designated as a dry year. Since 1939, 194, 1943, 1951, 1963 and 1971 have been dry years. Serious droughts all occurred in these years.
compared with the precipitation from April to June, the precipitation from July to September is obviously reduced. During this period, it is easy to form drought in summer and autumn.
the precipitation is the least from October to December. The precipitation from January to March is second to that from July to September.
the average annual precipitation is 176 mm, with the highest in 1997 reaching 2791 mm and the lowest in 23. The ratio of the average annual precipitation days to the days without precipitation for many years is 18: 2, which is not much different. The agricultural proverb says, "There are as many rainy days as there are sunny days". Since 1939, the maximum daily rainfall was 218.1 mm on June 18th, 1959 and June 1st, 1984.
sunshine: the average sunshine for many years is 1938.8 hours, the sunshine percentage is 44%, and the annual average total solar radiation is 112,189.9 calories/cm2.
frost-free period: the average frost-free period in the county is 279 days. The longest is 319 days and the shortest is 224 days.
the average first frost date is November 3th. The earliest first frost date is November 5, and the latest is January 3 of the following year.
the average final frost date is February 22nd. The earliest final frost date is January 16th, and the latest is March 28th.
The average number of days between the first and last frost (frost date) is 85 days for many years. The longest is 128 days and the shortest is 32 days.
The first frost is early and the last frost is late in the north of the county, and the frost period is longer and the frost-free period is shorter than that in the south. According to the observation records of the county meteorological bureau, there are fewer frosts on the top of the mountain and more frosts in the intermountain basin. As the saying goes, "the snow is high and the mountains are frosted."