What is suitable for Xichang in April?
trait
1. It is warm in winter and cool in summer, and the four seasons are like spring.
Xichang is controlled by warm and humid monsoon in southwest and southeast in summer, with concentrated precipitation, not hot in midsummer, and cool and humid in summer and autumn. Affected by the polar continental air mass in winter, the high altitude is controlled by the dry and warm westerly airflow in the south branch, and the winter is very warm, forming the climate characteristics of "no severe cold in winter, no high temperature in spring, no intense heat in summer, and cool in early autumn". There are many sunny days, strong solar radiation during the day, the ground temperature rises sharply, the clear sky radiation is lost at night, the temperature drops rapidly, and the temperature difference between day and night is large. There is a saying that "there is no winter and summer in a year, and there are four seasons in a day". The annual temperature difference is small and the daily temperature difference is large. The annual average temperature difference is only 13C, which is one of the regions with the smallest annual average temperature difference in China.
2. Abundant rainfall and concentrated rainfall
The rainfall in Xichang is concentrated, and 93% of the annual rainfall is concentrated in the summer half year. Night rain rate is high in rainy season, and the amount of night rain accounts for about 75% of the annual rainfall. During the day, the temperature in the mountainous area around the basin is low and the temperature rises slowly, and the air sinks, which is not conducive to water vapor condensation and less rain. The temperature in the basin rises rapidly in the afternoon, and the air around the basin rises along the hillside at night, which is conducive to the condensation of water vapor, so it is rainy. The Indian Ocean monsoon brings a lot of water vapor, and also forms unstable air stratification, which is prone to thunderstorms, often at night, and it rains after dawn.
3. Sufficient sunshine and abundant light and heat resources.
Xichang is high in altitude, low in latitude, with large solar altitude angle, many sunny days, many sunshine hours, strong ultraviolet rays, high wind speed, large evaporation of water vapor, low humidity, few foggy days and good visibility. Its sunshine is the high value center of the same latitude zone, and its accumulated temperature meets the needs of crop growth in four seasons. The ground temperature is higher than the air temperature, and the evaporation is greater than the precipitation. In winter and spring, the weather is often refreshing, sunny during the day and breezy at night, so it is called "Moon City".
The four seasons are not obvious, and the dry and wet seasons are distinct.
Xichang 65438+February-March is the dry season, and June-September is the rainy season. In the dry season, the climate is dry, the temperature is high during the day and afternoon, the daily temperature difference is large, the sunshine time is long, and the ground wind is strong in the afternoon. The rainy season is characterized by concentrated precipitation, abundant rainfall, small daily temperature difference, rainy days and rainy nights. In addition, in this season, air stratification is very unstable, convection is strong, and thunderstorms and hail are frequent. Due to the different monsoon intensity and advance and retreat time, precipitation is unevenly distributed in time and space, and it often suffers from natural disasters such as drought and flood.
In the transitional season, the climate is changeable
April-May in Xichang and 10- 1 1 are the seasons of air flow changes in winter and summer, which are called transition seasons. April-May is the transition from dry season to rainy season, which has both dry season climate characteristics and some rainy season climate characteristics. The solar altitude angle is increasing, the atmosphere receives more and more solar radiation, the warm air is gradually strengthened, the cold air is gradually weakened, the cold and warm air alternate frequently, and the weather is changeable. In April, the afternoon wind is still very strong. In May, due to the northward withdrawal of the upper jet, the southwest wind weakened obviously in the afternoon, and the upper circulation situation was changing to the rainy season. The atmosphere is often unstable, and cloud cover, thunderstorm, hail and rainfall increase. 10- 1 1 is the transition from rainy season to dry season. The basic climate characteristics in rainy season gradually decrease, while those in dry season gradually increase. The south branch airflow is obviously strengthened and expands southward. The scale of westerly ridge is obviously increased, the intensity of cold air is strengthened, the subtropical high is weakened and retreated southward, the summer monsoon is weakened until it disappears, and the water vapor transport is obviously reduced. Six. The climate in mountainous areas is three-dimensional and diverse.
Xichang is located in the plateau, with prominent vertical belt and large height difference. The temperature decreases with the elevation. Every altitude 100 m, the temperature drops by about 0.6℃, the active accumulated temperature drops by 282℃, and the frost-free period decreases by 12 days. The alpine valleys in China can be roughly divided into six climatic zones according to different slopes: 1200- 1300m is equivalent to the tropical climate in South Asia; 1300- 1800 m is in the middle subtropical zone; 1800-2 100 meters is north subtropical; 2 100-2500m is the south temperate zone; 2500-3000 meters is the middle temperate zone; Above 3000 meters is the north temperate zone. Luoji Mountain and Yak Peak have no summer all year round, and Yalong River has no winter all year round. Therefore, the climate of Xichang has three-dimensional climate characteristics: "the top of the mountain is cold, the mountainside is mild, and the valley is dry and hot" and "one mountain is divided into four seasons, and ten miles are different from the sky". The diversity of climate resources is beneficial to crop growth in different climatic zones.
Accumulated temperature and ground temperature
1. temperature
The average temperature in Xichang is 17.2℃, with the highest temperature of 23.8℃ in August and the lowest temperature of 9.4℃ in1October. The absolute maximum value is 35.0℃ and the absolute minimum value is -2℃, which appear in June of 1927 and 1933, and in June of 1930 and 1935 respectively. Generally, the temperature is moderate, and the temperature difference between morning and evening is large. The temperature difference is often around 10℃, and the temperature in each season is not much different. The average temperature in July is 22.5℃ for many years, and the average temperature in Leng Yue is 9.5℃ in October. The annual temperature is 13.0℃, which is one of the areas with the smallest temperature change in China. The range of monthly relative temperature is 0.8% in May-June, 35. 1% in February-March, 10-165438+28.3%. The temperature rises early and sharply in spring, and drops rapidly in autumn, which is higher than that in autumn. The extreme minimum temperature of -3.8℃ appeared on February 9 1977, and the low temperature intensity was not great. The highest extreme temperature was 36.6℃, which appeared on May 3 1983+0. The daily temperature difference is large, with a monthly average of 14. 1℃, which is 4℃-6℃ higher than that in Sichuan Basin. From late March to September, the average number of days with the highest temperature above 30℃ is 40.3 days, with the highest being 57 days in 1957 and the lowest being 10 days in 1974, with the highest being 12 days in May and only 2.6-6.9 days in other months. The highest temperature of 35℃ has 23 days in 8 of the 30 years, with an average of 0.76 days in 30 years, all of which occurred from mid-May to early June. The longest years are 1954 and 1963, reaching 5 days per year. The lowest temperature occurs from the first ten days of 65438+February to the second ten days of the following year, and the number of days is less than or equal to 0.0℃, with an average of 5 days in 30 years, February 1.8 days,1October 65438+2.7 days and February 1.6 days. The longest year is 1976 and 1977, the earliest year is 1954 and 1968, and the last year is 1968, February 24th.
According to the meteorological average temperature, the coldest January is also 65438 0.7℃ higher than Kunming, the "Spring City". People think that the hottest season is May before the rainy season. Before the rainy season comes, the solar radiation is strong, and the temperature rises sharply during the day. The actual average temperature in May is only 265438 0.2℃, because the temperature at night is much lower than that in July and August in midsummer. Xichang midsummer has changed from dry season to rainy season. It is rainy and cloudy, the solar radiation is weakened, and the ground evaporation consumes heat. So midsummer is also warm, cool, pleasant and the hottest? Comparing the tourist attractions at home and abroad, Lushan Mountain is 22.6℃, Hengshan Mountain is 2 1.6℃, chengde mountain resort is 24.4%, Qingdao is 25.4%, Kunming 19.8%, Paris 19.8%, Rome is 24.7%, new york is 24.9% and Tokyo is 25. In the mountainous area around Xichang Basin, according to the measured record of Yak Peak TV relay station in Kaiyuan Township at an altitude of 34 1 1 m, the highest temperature in the whole year is 13℃, and the lowest temperature is-17℃.
Two. cumulative temperature
The average daily temperature in Xichang is stable, with initial, final and accumulated temperatures ≥0.0℃, 5.0℃, 10.0℃ and 15.0℃ respectively. The average accumulated temperature of 30 years ≥0.0℃ is 6206.2℃, the interval between the first day and the whole day is 365.3 days, and the highest year is 19500 days. Accumulated temperature ≥5.0℃ is 6 148.5℃, and the starting and ending days are 357.2 days. The highest year is 65438+6539.3℃ in 0952, and the lowest year is 5533. 1℃ in 974. The accumulated temperature ≥ 10℃ is 5329.9℃, the first day is February 25th, the whole day is165438+1October 29th, and the days from the first day to the end are 277.6 days.
Sunlight evaporation humidity
First of all, sunshine
Xichang has strong solar radiation and abundant sunshine. According to the observation of 195 1- 1990, the annual average sunshine hours are 2432. 1 hour, accounting for 55% of the available sunshine hours, with the longest reaching 2660.5 hours (1980) and the youngest reaching 2. It is 200-500 hours longer than Tengchong and Deqin in the west, 500- 1000 hours longer than Guiyang, Zhijiang, Fuzhou, Changsha, Nanchang and Wenzhou in the east, and 1203 hours longer than Chengdu. The high-value period is half a year in winter (65438+ February to May of the following year), with an average monthly sunshine of more than 200 hours, accounting for 60%-70% of the available sunshine hours, with the highest sunshine hours in March, accounting for 76% of the available sunshine hours; The low value period is in the summer half year (6-165438+1October), and the average monthly sunshine hours are between 144- 199 hours, accounting for only about 30%-40% of the available sunshine hours, with the lowest sunshine from June to September.
The total solar radiation value of Xichang is 136.2 kcal per square centimeter, and the physiological radiation value is 64 kcal per square centimeter. The total radiation is 45 kcal more than Chengdu, 13.4 kcal more than Kunming and 37 kcal more than Changsha. The highest in April is 14.7 kcal per square centimeter, and the lowest in February is 8.7 kcal per square centimeter.
Sunshine during the growing period of main crops in Xichang: Da Chun grain crops 1.228 hours (6.7 hours per day), the highest year 1.956 reached 1.384 hours, and the lowest year 1.954 only had 964 hours. Equivalent to the total sunshine hours in Chengdu and Leshan throughout the year; The grain crops in Koharu 1.542 hours, the highest year 1.726 hours and the lowest year 1.339 hours, which is more than the total sunshine of all counties in Sichuan Basin. The growth period of sericulture is longer than that of ningnan county 174 hours and Nanchong 1077 hours. Especially from May to June 10, the sunshine in Xichang is 53 hours longer than that in Ningnan and 160 hours longer than that in Nanchong, and the light quality is higher than that in Sichuan Basin. During the growth period of flue-cured tobacco, the sunshine in Xichang from May to September is 40 hours more than that in Huili and 73 hours more than that in Yuxi, Yunnan. Xichang has great potential of light energy, and its utilization rate is very low at present. The utilization rates of rice and corn are only 1.5%, wheat is 1. 1%, and rape is only 0.4% (calculated by average yield 1982). Even if it reaches the highest yield level in Xichang, its light energy utilization rate is only 3.3% for rice, 6.0% for corn, 3.6% for wheat, and 0/0/.5% for rape. At present, the maximum utilization rate of short-term light energy in China has reached 5%
Second, evaporation.
Xichang is located in the plateau, with abundant sunshine, high ground temperature and temperature, high wind speed, less precipitation and large evaporation in winter. Measured by the National Meteorological Administration in 27 years, the average evaporation for many years is 1.945 mm, while the average rainfall for many years is only 1.004.3 mm, with a deficit of 940.7 mm and a deficit rate of 93.66%. Except for the rainy season in June and September, the rainfall is greater than the evaporation, and the evaporation is greater than the rainfall in the other eight months. The evaporation is the largest from March to May, with an average of 239.8-262.5 mm per month, especially in Xichang in early spring.
Three. humidity
The relative humidity in Xichang has been relatively small over the years, and the change is relatively stable. 195 1- 1980, with an average of 6 1%, the highest average of 65% and the lowest average of 58%. The average humidity in June 6- 10/0 is 73%-75%, and it is as high as 8 1% in four months in 30 years. The average value from February to April is only 4 1%-46%, which is the lowest period in the whole year, and the lowest value is only 32% in four years and four months. The relative humidity is the lowest in March and April, and the humidity is O for two months and three days in 30 years, reaching a very low value. The relative humidity in Qionghai Basin in the east can reach 70%, while that in Yalong River Basin in the west is only 60%.
Fall into the water
1. Rainwater
Xichang is controlled by the southwest monsoon of the Indian Ocean, and the rainfall is concentrated in the summer half year, with the same season of rain and heat and abundant rainfall, which is beneficial to crop growth. However, due to the uneven distribution of rainfall in time and space, droughts in winter and spring and floods in summer and autumn often occur, and rainfall shows a slow downward trend. According to the Republic of China
After liberation, the average annual rainfall of 195 1- 1980 was10/3.1ha,1951-.
195 1 to 1980, the maximum rainfall is 147 1. 1.2 mm in 0968, and the minimum rainfall is only 65438+69/kloc-in 0962. The annual average rainfall is more than 9 years 1 100 mm, including 6 years in 1950s, 2 years in 1960s and 70s 1 year. There are also 9 years when the annual average rainfall is below 890 mm, including 2 years in 1950s, 3 years in 1960s and 4 years in 1970s. There is a downward trend in rainy years and an upward trend in rainy years. Over the years, the rainy season mostly started in the middle and late May and ended in the middle and late October of 10, and the rainfall was about 93% of the annual rainfall. The early season generally begins in U month and ends in late April and early May of the following year, and the rainfall only accounts for about 7% of the annual rainfall.
There are many rainy days in Xichang. According to the statistics of 195 1- 1980 for a total of 360 months, there were no continuous rainy days in 16 months (4%) in the winter half year, and there were continuous rainy days in the remaining 344 months (96%), with rainfall of 0./kloc-0. The maximum time is July 1954, with continuous rainfall of 27 days and rainfall of 282.4 mm; The rest of the year is usually 8-22 days, and the rainfall is100.5-253.0mm. The continuous heavy rainfall is an important cause of floods and mudslides in Xichang.
The night rain rate in Xichang is high (refers to the rain from 18:00 to 8:00 the next day). The night rainfall is 756 mm, accounting for 75% of the annual rainfall, and the daytime rainfall is 242 mm, accounting for 25%. According to the statistics of rainfall time in xichang satellite launch center1974-1983 May-10, the number of rainy nights accounts for 62% of the total number of rainy days, and the amount of rainy nights accounts for 68% of the annual rainfall. The rainy days in the daytime only account for 2 1.7% of the total rainy days, and the rainfall only accounts for18% of the annual rainfall. All-weather rainy days account for about 12%.
The continuous rainy days in Xichang are also very prominent, mainly from 65438+February to March of the following year. The smallest is 65438+65438 from1October 15 to 0965+2 1 day on February 4th, and the largest is 97 days from 1978 12 to 19. The spring drought in Xichang was aggravated.