What is plum rain and what is summer drought?

Drought that occurs during the Futian period is called Fu (summer) drought, which is a disastrous climate in the monsoon area.

It mainly occurs in the Yangtze River Basin and Jiangnan region of my country, especially in Hubei, Hunan, Jiangxi, Jiangsu, Anhui and other provinces. When the subtropical high in the western Pacific is controlled and there is little typhoon activity, severe drought is likely to occur and precipitation is significantly less than the multi-year average. Generally from mid-July to mid-August. (Dotian begins on the third Geng Day after the summer solstice, approximately 10 days after July 12 every year.)

The quasi-stationary front that caused the Meiyu has moved to the middle and lower reaches of the Yellow River and the Yellow River in early July. In the northeastern region, the middle and lower reaches of the Yangtze River are controlled by the subtropical high pressure zone, forming anticyclonic weather, dominated by downdrafts, with long sunshine, strong solar radiation, high temperatures, and strong evaporation. Crops also grow quickly and farmland requires a lot of water. However, due to the single air mass, except for thunderstorms in local areas, there are no large rainy areas. Dry and hot weather generally occurs, so it is called "Fu Drought". During this season, afternoon temperatures in the middle and lower reaches of the Yangtze River generally reach 33 to 35°C, and high temperatures as high as 43 to 45°C are recorded in some places. Generally, severe drought is likely to occur when the western Pacific subtropical high pressure is controlled and there is little typhoon activity.

It is characterized by strong solar radiation, high temperature, low humidity, large evaporation and transpiration, making it the hottest period of the year. Under the control of the western Pacific subtropical high, the Yangtze River Basin in my country is sunny, hot and rainy, and droughts occur more frequently, up to 50% of the time. Other areas also experience summer drought in some years. Summer is a period of vigorous growth of crops. Although summer droughts are not as frequent as spring droughts, they are generally more harmful to crops than spring droughts. Therefore, there is a farmer's proverb that "spring droughts are not considered droughts, but summer droughts are reduced by half." Drought is not only related to the growth of crops that year, but also determines the water storage capacity of reservoirs and the formation of soil moisture in that year, which has an important impact on the growth and yield of winter wheat and spring sown crops in the coming year.

Introduction to Meiyu

A long period of gloomy and rainy weather often occurs in the Jianghuai River Basin in early summer. At this time, utensils are prone to mold, so it is also called "mold rain", or "mold" for short. It is also the time when plums in the south of the Yangtze River are yellow and ripe, so it is also called "plum rain" or "yellow plum rain". There are many records in Chinese historical records. For example, "Ji Xue Ji" quoted from the "Compiled Essentials" of Emperor Liang Yuan of the Southern Dynasties, "When the plum blossoms are ripe and it rains, it is called plum rain." "Plum Rain" by Liu Zongyuan of the Tang Dynasty: "The plum blossoms are solid to welcome the rain, and the vastness is in late spring." etc. The Chinese almanac has records of the beginning and end of mildew rain: the day it begins is called "mold entering" and the day it ends is called "mold comes out." Mold will appear on the first C day after Eawn is planted, and mold will appear on the first day after Slight Heat. The onset of mold is usually between June 6 and 15, and the onset of mold is between July 8 and 19. There is an obvious rainy season in eastern China with a long rain period and relatively concentrated rainfall. The main rain direction is generally east-west. It is caused by the north-south displacement of the belt and is a unique phenomenon during the seasonal changes in the East Asian atmospheric circulation at the turn of spring and summer. After mid-June, the rain belt remains in the Yangtze-Huaihe River Basin, which is the Meiyu period. The residence time of the rain belt is called the "Meiyu season". The day at the beginning of the Meiyu season is called "Meiyu season" and the day at the end is called "Meiyu season".

In addition, due to the high humidity of the air during this period, everything is easy to get damp and moldy, so people gave Meiyu another name, called "mold rain". The "Wuza Ju? Tianbu Yi" written by the Ming Dynasty in Hangzhou records: "Every year in the third and fourth months of the year in the south of the Yangtze River, the bitter rain will not stop, and everything will become moldy and rotten. It is commonly called plum rain, when the plums are green and yellow. Since Xu To the north of the Huaihe River, there is constant drought in spring and summer. At the turn of June and July, the rain will not stop and everything will become moldy." Li Shizhen, an outstanding medical scientist in the Ming Dynasty, pointed out clearly in the "Compendium of Materia Medica": "The plum rain may cause mold rain, and black mold will appear on clothes and objects."

Meiyu and Rain Belts

1. Meiyu

In the middle and lower reaches of the Yangtze River in my country, the Meiyu season is usually around mid-June to early July every year. The sky has been gloomy for days, and the precipitation has been continuous, sometimes heavy and sometimes light. Therefore, there is a popular proverb in southern my country: "The rain hits the yellow plum blossoms, and there is no sun for forty-five days." Continuous rain, high temperature and high humidity are the main characteristics of Meiyu.

Very different from the climate in areas at the same latitude, Meiyu refers to the weather and climate phenomena that occur in a certain area and in a certain season. Research has found that the Eurasian continent is between 20N and 40N, a zone alternately controlled by subtropical high pressure and westerly belts. On the west coast of the continent, in summer, controlled by the downdraft on the east side of the subtropical south pressure, the weather is sunny and cloudy, and the climate is hot and dry; in winter, under the influence of the westerly wind belt, warm and humid air is brought from the Atlantic, forming more precipitation, making the climate milder Rainy.

That is, it has a subtropical Mediterranean climate with dry summers and wet winters.

On the east coast of the mainland, in summer, it is controlled by the west side of the subtropical high pressure. The sinking air is originally dry, but it absorbs a large amount of water vapor from the warm and humid sea surface, thus bringing abundant precipitation and creating a humid subtropical climate. Due to the strong contrast between sea and land, a unique monsoon climate is formed here. Its notable feature is summer rain and winter dryness, with rainfall concentrated in summer, which is exactly the opposite of the Mediterranean climate.

If compared with the east coast of the UK at the same latitude, it is completely different. There will be no long-term rainy weather before and after the summer monsoon in the mid-latitude areas of the east coast of the United States. People will never feel the long-term muggy weather, and mold is unlikely to occur. It can be seen that the precipitation seasons are very different at the same latitude. Therefore, in the world, yellow plum appears only on both sides of the middle and lower reaches of the Yangtze River in my country, roughly starting from the east of Yichang and in the area between 29 and 33 degrees north latitude, as well as in southeastern Japan and the southernmost part of the Korean Peninsula. In other words, Meiyu is a unique weather and climate phenomenon in East Asia, and in my country it is a unique weather and climate phenomenon in the middle and lower reaches of the Yangtze River. < /p>

②The westerly circulation in the mid-latitudes is flat, and frequent shortwave activities provide cold air conditions for the Jianghuai region;

③The western Pacific subtropical high has an obvious westward and northward jump process, and the 500hPa subtropical high The high ridge line is stable between 20 degrees and 25 degrees north latitude, and warm and moist airflow is transported from the edge of the subtropical high to the Jianghuai basin. Under such circulation conditions, the Meiyu front lingers in the Jianghuai basin, often accompanied by southwest vortices and shear lines, and mesoscale systems are active above the Meiyu front. It not only maintains continuous rainfall during the Meiyu period, but also provides abundant water vapor for heavy rains.

Meiyu front heavy rain is a kind of special weather in a specific area formed by the interaction of circulation systems of different scales. The variability of atmospheric circulation causes the Meiyu period to start later or earlier each year, and the Meiyu duration to vary. Some years are short, and some years, the Meiyu front is particularly active, with frequent heavy rains, causing floods. In some years, the plum rain front is not obvious and "empty plum rain" appears, resulting in dry weather. In some years, the plum rain belt moves northward and then returns to the Yangtze-Huaihe River Basin to remain relatively stable again. It is customarily called "Inverted Huangmei". After the rainy season in the Jianghuai River Basin ended, the rain belt moved to North China, and the Jianghuai River Basin entered a period of high temperature and little rain.

2. Rainbands

Although Meiyu is a unique weather and climate in the middle and lower reaches of the Yangtze River, its occurrence is not isolated. It is closely connected with the north-south displacement of large-scale rainbands. of.

In the eastern region of my country east of 110E, during the flood season from mid-May to early June, the main rainbands swing over the Nanling Mountains and the area south of Nanling. In individual years, although it moves to the north of Nanling within a certain period of time, judging from the multi-year average situation of a pentad (a pentad of five days) or a ten-day period, it tends to remain south of 28N and 29N. This period is called the "Jiangnan Rainy Season" or the "South China Pre-Flood Season".

In mid-to-late June, the main rain belt moves northward to the range of 29N-33N (i.e., from Yichang, my country in the west, to the Yangtze River Estuary in the east, and then across the sea to Japan; from the Lianghu Basin in the south to the south bank of the Huaihe River in the north) , stable and less moving. At this time, the area south of Nanling was outside the rain belt, and the rainy weather ended; while the middle and lower reaches of the Yangtze River bid farewell to the sunny early summer and ushered in the rainy season, with heavy rains and heavy rains appearing from time to time, which lasted until In early July, this is the famous plum rain season in the middle and lower reaches of the Yangtze River.

Beginning in mid-July, the rain belt moved northward again, reaching the area north of 33N. It has stagnated and lingered in the Yellow River, Huaihe River Basin, North China, Northeast China and other places, causing heavy rainfall again and again, which are called "Yellow-Huaihe Rainy Season" and "North China Rainy Season" respectively. At this time, the plum rain in the middle and lower reaches of the Yangtze River ends, and the scorching sun hangs high. Entering the hot summer season. This kind of weather lasted until late August, and then the rain belt quickly retreated southward as the cold air gradually became active. In less than a month, the rain belt retreated all the way to the coastal areas of South China. This regular change of rain belts shows that the Meiyu in the middle and lower reaches of the Yangtze River is not an isolated, local weather and climate phenomenon, but an integral part of the main rainy season activities in eastern my country. It is the main rain belt moving northward along the Yangtze River. A reflection of the stagnation in the middle and lower reaches.

Normal Meiyu and Abnormal Meiyu

Meiyu is a unique weather and climate phenomenon in the middle and lower reaches of the Yangtze River in early summer. It is the result of the main rain belt in eastern my country stagnating in the Yangtze River Basin during its northward movement. , the rainy season ends and midsummer arrives. This seasonal change and the movement of rain belts with the seasons are roughly the same every year, forming a certain climate regularity. However, the plum rains are not completely consistent every year, and there are large inter-annual variations.

In meteorological terms, the start and end times of plum rain are called "incoming plum" (or "rising plum") and "out of plum" (or "broken plum") respectively. In the middle and lower reaches of the Yangtze River in my country, the plum blossom season begins in mid-June and blooms in early July on average every year, which lasts for more than 20 days. However, for each specific year, there are great differences in the morning and evening when the plum rain begins and ends, and the intensity of the plum rain. As a result, the plum rain is obvious in some years, not obvious in other years, and even causes the phenomenon of empty plum rain. For example, the plum rainy season in 1954 lasted for more than two months, causing a rare flood year in history in the middle and lower reaches of the Yangtze River. In 1958, the plum rainy season lasted only two or three days, resulting in a drought year rare in history.

(1) Normal plum rain:

The normal plum rain in the middle and lower reaches of the Yangtze River begins in mid-June and ends in mid-July, which is when the "Grand Grain" and "Summer Solstice" occur. Within two solar terms. The Meiyu period lasts about 20-30 days, with rainfall ranging from 200-400 mm. Starting around "Small Heat", the main rainfall belt moves northward to the Yellow River and Huaihe River basins, and then to Shandong and North China. The weather in the Yangtze River Basin has begun to change from rainy, hot and humid weather to sunny and hot midsummer. According to statistics, this kind of normal plum rain accounts for about half of the total.

(2) Early plum rain:

In some years, the plum rain starts very early, and will suddenly arrive at the end of May or early June. Meteorologically speaking, the plum rains that start before the "grain" are usually collectively referred to as "early plum rains". Early plum rains will bring some abnormal phenomena. For example, during the period when the plum rain has just begun, cold air from the north to the south is still very frequent in the atmosphere close to the ground. Therefore, after the rain begins, the temperature is still relatively low and even feels chilly. The farmer's proverb says: " This is what it means if you eat Dragon Boat Festival brown rice, you have to freeze it for three times. At the same time, there is no obvious moisture phenomenon. Farmers in some areas of the middle and lower reaches of the Yangtze River call the relatively low-temperature yellow plum rain in this section "cold water yellow plum rain". In the future, as the rainy season lasts longer and the warm and humid air intensifies, the temperature will gradually rise, the humidity will continue to increase, and the inherent characteristics of plum rain will become more and more obvious. The chance of early plum rains is roughly once every ten years. This early plum rain often presents two situations. One type starts early and ends late, and even ends in late July. The rainy period lasts forty to fifty days, and in some years it lasts for two months. The other is that it starts early and ends early. By late June, the middle and lower reaches of the Yangtze River have entered midsummer. Due to the early arrival of midsummer, droughts of varying degrees in the middle and lower reaches of the Yangtze River are often caused.

(3) Late Meiyu:

The opposite of early Meiyu is belated Meiyu. Meteorologically speaking, the Meiyu that starts after late June is usually called late Meiyu. There are more chances of late plum rains than early plum rains. Since the solar term is relatively late when the Late Meiyu Rain begins, once the warm and humid air moves northward, it is very powerful. At the same time, the solar radiation is also relatively strong. After the air is heated, intense convection is prone to occur. Therefore, the Late Meiyu Rain is often accompanied by thunderstorms and showers. People also call this yellow plum rain "the first yellow plum rain". The duration of late plum rain is generally not long, only about half a month on average. However, the rainfall during this rainy season is sometimes quite concentrated.

(4) Extraordinarily long plum rain:

In 1954, a once-in-a-century flood occurred in the Jianghuai River Basin of my country. This flood was caused by a particularly long-lasting plum rain. This year, there was a lot of spring rain in the second half of May before the plum rain began in the middle and lower reaches of the Yangtze River. The plum rain came very early again, starting in early June. The weather has been cloudy and rainy all the time, and there have been heavy rains and torrential rains from time to time, which lasted for a particularly long time, and the plum blossoms did not appear until early August. When the rain ends and the weather turns to midsummer, it is already approaching the "beginning of autumn". The entire Meiyu period lasts for two months this year, and together with the spring rain in May, it lasts for more than two and a half months. After entering the "little heat" and "big heat", the middle and lower reaches of the Yangtze River should have been sunny and hot "dog days", but it has always been cloudy and it is difficult to see the sun. From time to time, heavy rain pours to the ground, and floods are rolling in many areas." The cold air hits people.

The rainfall in the middle and lower reaches of the Yangtze River in the three months from May to July generally reaches 800-1000 millimeters, which is close to the annual rainfall in the region in normal years; in some areas, the rainfall is as high as 1500-2000 millimeters, which is equivalent to the same amount in the same period. The area receives a lot of rainfall for a year and a half, resulting in widespread flooding. Our country has a vast territory and local floods often occur. Some may be caused by typhoon rain, and some may be caused by several heavy rains brought by other weather systems, but they do not last long, the floods recede relatively quickly, and the scope of their impact is relatively small. It is extremely rare for rainy weather to last for more than two months like in 1954, causing floods in the entire Yangtze River Basin. This rare flood is often associated with unusual plum rains. The floods in 1998 were also caused by the particularly long rainy season.

(5) "Short Plum" and "Empty Plum":

Completely opposite to the particularly long plum rain, in some years the plum rain is very inconspicuous, it seems to come and go in a hurry. Passers-by, after staying in the middle and lower reaches of the Yangtze River for more than ten days, they hurried north. Moreover, there is not much rainfall during this period, with one or two heavy rains being rare. This situation is called "short plum". What's more, in some years, there has been no continuous rainy weather in the Yangtze River Basin since early summer. Most days are sunny and warm during the day, and very cool in the morning and evening. The weather is "dry and loose during the yellow plum season". The mildew on clothes that usually occurs during the rainy season has almost never happened. This period of cool weather is over. Then it turned into midsummer. Such a year is called "empty plum". The average chance of "short regret" and "empty plum" appearing is 1-2 times in ten years. In years with "short plum blossoms" and "empty plum blossoms", latent drought often occurs, and in some years it can even cause severe drought.

(6) Inverted Huangmei:

In some years, the Huangmei weather seems to have passed in the middle and lower reaches of the Yangtze River, and the weather has become sunny, the temperature has risen, and the characteristics of midsummer have appeared. However, a few days later, hot and humid thunderstorms and showers reappeared and lasted for quite some time. This situation is as if Huang Meitian is turning back and returning to the middle and lower reaches of the Yangtze River, so it is called "Inverted Huangmei". "There is a thunder in Xiaoshu, and Huangmei turns upside down." This is a weather proverb widely circulated in the middle and lower reaches of the Yangtze River. It means that after the plum rain has passed, if thunder occurs during the "Small Heat", the plum rain will reverse again. There is some truth to this. Because after the Meiyu rain ends, the weather in the middle and lower reaches of the Yangtze River usually becomes more and more stable, but thunderstorms are a symbol of unstable weather. Moreover, when it comes to "Slight Heat", usually cold air no longer affects the Yangtze River Basin, and the occurrence of thunderstorms is often related to the southward flow of small cold air from the north. This southward flow of cold air is conducive to the re-establishment of rain belts in the middle and lower reaches of the Yangtze River. Of course, "fallen yellow plums" do not necessarily appear after thunder on Xiaoshu days. Generally speaking, "Inverted Huangmei" does not last long, ranging from about a week to ten and a half months. However, during the "Huangmei" period, due to frequent thunderstorms and showers, the rainfall is often quite concentrated, which needs to be noted. Since "Inverted Huangmei" is a type of plum rain, it usually turns to sunny and hot weather after it ends.

From the various plum rains introduced above, we can see that Huang Meiyu, which is usually regarded as similar by people, is actually diverse, and the differences between them are sometimes quite disparate. . For example, the earliest plum blossom season is on May 26 and the latest plum season season is July 9; the earliest plum season season is on June 16 and the latest plum season season is on August 2. The difference can be as much as one. Half a month. In the longest years, the plum rain lasts for more than two months, which can cause rare floods, while in short years, it lasts only a few days, and some even cause "empty plum rain", which can cause severe drought. It can be seen that plum rain is a complex weather and climate phenomenon. It is far from as simple as the "incoming plum rain" and "out of plum rain" specified in the lunar calendar. Compared with normal plum rains, "early plum rains", "late plum rains", "extremely long plum rains", "empty plum rains" and severe "inverted yellow plum rains" are all abnormal plum rains.

The weather process of Meiyu in the Jianghuai River Basin of my country

How is Meiyu formed? To answer this question, we actually need to figure out how the rainbands stagnant in the middle and lower reaches of the Yangtze River are caused. To this end, we need to start with the high and low-altitude atmospheric circulation conditions during the Meiyu period to understand the weather process during the Meiyu period.

The ground situation during the Meiyu period

The middle and lower reaches of the Yangtze River are located in the mid-latitudes of eastern Eurasia. On the one hand, they are affected by the cold air coming south from the frigid zone, and on the other hand, they are affected by the The influence of warm and humid air moving northward over the tropical ocean. Starting from spring every year, the force of warm and humid air gradually strengthens, entering the mainland from the sea, first reaching South China, and then further strengthening and moving northward. In early summer, it often extends to the middle and lower reaches of the Yangtze River, and sometimes reaches the Huaihe River and the areas north of it. Especially at low altitudes of two to three thousand meters, there is often a very moist and strong southerly airflow coming from the ocean, with wind speeds reaching about ten to twenty meters per second. When it enters mainland my country, it encounters cold air moving from the north to the south. When cold and warm air meet, a front forms at the junction, and precipitation occurs near the front. Meiyu is characterized by frontal precipitation.

If the cold air is strong, the cloud and rain areas will move southward with the cold air; if the warm air is strong, the cloud and rain areas will move north with the warm air. Obviously, in both cases, they don't stop in one area. But in early summer, in the middle and lower reaches of the Yangtze River, on the one hand, the warm and humid air is already quite active, on the other hand, the cold air moving from the north to the south still has a certain amount of power. Especially in the air layer close to the ground, there are often small gusts of air. A small wave of cold air moves southward. In this way, cold and warm air confront each other in this area, competing with each other to form a stable rainfall belt. This rain belt is only 200 to 300 kilometers from north to south, but can reach about 2,000 kilometers from east to west. It traverses the middle and lower reaches of the Yangtze River and stretches eastward to Japan. It is the influence of this rain belt that causes the plum rain in Japan to be very obvious.

This rainband also tends to have a relatively small north-south swing in a short period of time. When the cold air strengthens, it moves slightly south; when the warm air strengthens, it moves north again. When this narrow rainband makes a small swing in the north-south direction, the area near the rainband will have weather that is sunny and rainy. In this rain belt, there are centers with relatively high rainfall intensity from time to time. Heavy rains or torrential rains often occur in areas where the rainfall center passes through.

In fact, this rainfall band is the interface formed by the cold and warm air front - the product of what is usually called the "front" in weather broadcasts. However, this front is different from ordinary fronts in many ways. First, this front is particularly stable. Not only does it not move as obviously as "cold fronts" and "warm fronts", but it is also different from ordinary "stationary fronts". Usually, a "stationary front" can only stay in one area for one or two days, and as many as three or four days. However, the period when the Meiyu front was active in the Yangtze River Basin was a period between two sudden changes in atmospheric motion in the vast area of ??East Asia. During this period, the cold and warm air met in the middle and lower reaches of the Yangtze River for a long time, and the two sides were evenly matched. , each refusing to give in, in a see-saw state. As a result, this front and its rainfall belt are particularly stable for a long period of time, bringing continuous rainy weather to the middle and lower reaches of the Yangtze River; secondly, the difference in the properties of cold and warm air on the north and south sides of the Meiyu front is mainly reflected in the air In terms of humidity, that is, the air from the ocean in the south has higher humidity, which is completely different from the dry and cold air in the north. The difference in temperature between the air on both sides of the front is much smaller than that of fronts in other seasons. After the cold air passes through, there is no obvious cooling; thirdly, its rainfall area is very narrow in the north-south direction, unlike in winter and spring. The front has a very wide rain area. However, the intensity of precipitation is much stronger than that in other seasons. Since these characteristics are unique to the Meiyu period, the meteorological community calls this front the "Meiyu front", and in professional terms it is called the "quasi-stationary peak".

Proverbs related to plum rain

There are many folk proverbs related to plum rain circulating in the middle and lower reaches of the Yangtze River in my country. We have collected some of them for the benefit of readers.

"Sanjiu owes the east wind, and Huangmei does not have heavy rain." "Sanjiu" refers to January 9-17 of the Gregorian calendar, and "Huangmei" refers to the solar term of Ear Grain (June 6-20). The meaning of this proverb is that if there is no east wind blowing during the March 9th period, or there is very little east wind, the rainfall during the Mangzhong solar term will also be less. The first day of Sanjiu is about 150 days apart from the first day of Mangzhong solar term. According to the 150-day rhythm, the east wind blows during the March 9th period, and there will be a similar repeating process every 150 days or so. Therefore, the east wind blowing during the March 9th period has a corresponding relationship with the precipitation during the Mangzhong solar term.

There are many proverbs that use winter weather characteristics to predict plum rain. For example, "There is a lot of snow in the twelfth lunar month, and the water is yellow and plum" means that there is a positive correlation between the snow in the twelfth lunar month and the plum rain.

"The water dries up in cold weather, and the water dries up in summer." "Dry" refers to less rain. As the proverb goes, if there is less rain in winter, there will be less rain in the plum season. This is because weather tends to have phases. Sustained drought weather is often caused by the relative stability of a certain weather situation that is conducive to drought. However, since the atmosphere is in constant motion, the above-mentioned relatively stable state will always be destroyed and transformed to the opposite direction under certain conditions.

"If all the peach blossom water is exhausted, it must be dry yellow plum blossoms." "Peach blossom water" refers to the precipitation during the Qingming solar term or during the peach blossom blooming period in April. "Dry Huangmei" refers to the lack of plum rain or the late start of plum rain in the Ear solar term. In the lower reaches of the Yangtze River, if there is more rain during the Qingming Festival or April when the peach blossoms are blooming, commonly known as "peach blossom water", the plum rain will be less during the Egzhong solar term, or the plum rain will start later. "The peach blossoms fall in the mud, and the wheat is beaten in the dust; the peach blossoms fall in the dust, and the wheat is beaten in the mud." This has a similar meaning. There is too much water in peach blossoms, which often indicates that the subtropical high pressure in the Pacific Ocean is stronger than usual in spring and the warm and humid air is active. During the Qingming Festival when peach blossoms bloom, they often confront the cold air from the north and south in the Jiangnan and Shanghai areas, resulting in peach blossoms. Too much water. During the Mangzhong solar term in June, the force of the subtropical high often weakens in updating, or jumps north slowly, resulting in less rain or a later start of the plum rain, resulting in an inverse correlation between the rainfall in the two periods.

"Spring water spreads, summer water dries up", "spreading" means that there is more rain than normal. The proverb explains that if there is too much rain in spring, there will be less rain in summer, and drought is likely to occur. It is the same as "when all the peach blossom water is gone, there will be dry yellow plum blossoms", which uses spring rain to predict plum rain.

"If there is spring breeze, there will be summer rain." Spring breeze refers to the easterly wind (mostly southeast wind), and summer rain refers to plum rain. The proverb means that in years with more easterly winds in spring, there will generally be more plum rains in summer.

"Xiaoman is dissatisfied, Huangmei doesn't care", which indicates that there is a positive correlation between rainwater between Xiaoman and Mangzhong solar terms, that is, if there is less rain in Xiaoman solar term, it means that there will be less rain in Mangzhong solar term, or Huangmei is late. This is because the Xiaoman solar term coincides with the turn of spring and summer. If there is less rain during this period, it reflects that the force of the subtropical high is weak and its location is southward. When it comes to the Mangzhong solar term, the force of the subtropical high will generally not strengthen quickly, even if it has a certain intensity. , the southwest airflow on its northern edge will not extend to the lower reaches of the Yangtze River, so there will be less rain in the lower reaches of the Yangtze River during the Mangzhong solar term. In the lower reaches of the Yangtze River, precipitation in the Xiaoman solar term is also called "dry yellow plum", precipitation in the Mangzhong solar term is called "zhenghuangmei", and precipitation in the summer solstice solar term is called "sweet yellow plum". Therefore, if there is less rain in Ear Grain or if the plum rain starts late (it does not start until the summer solstice), it is called "Huang Mei Guan".

The above-mentioned people’s sky-gazing experience has been verified by local meteorological data, and the accuracy rate is 70% to 80%. In other words, if a forecast is made out of ten, it will be correct seven or eight times. This shows that the proverb about plum rain is credible.

In early summer, a long period of gloomy and rainy weather often occurs in the Jianghuai River Basin. At this time, utensils are prone to mold, so it is also called "mold rain", or "mold" for short. It is also the time when plums in the south of the Yangtze River are yellow and ripe, so it is also called "plum rain" or "yellow plum rain". There are many records in Chinese historical records. For example, "Ji Xue Ji" quoted from the "Compiled Essentials" of Emperor Liang Yuan of the Southern Dynasties, "when the plum blossoms are ripe and it rains, it is called plum rain". "Plum Rain" by Liu Zongyuan of the Tang Dynasty: "The plum blossoms are solid to welcome the rain, and the vastness is in late spring." etc. The Chinese almanac has records of the beginning and end of mildew rain: the day it begins is called "mold entering" and the day it ends is called "mold comes out." Mold will appear on the first C day after Eawn is planted, and mold will appear on the first day after Slight Heat. The onset of mold is always between June 6 and 15, and the onset of mold is between July 8 and 19. There is an obvious rainy season in eastern China with a long rainy period and relatively concentrated rainfall. The main rain direction is generally east-west. It is caused by the north-south displacement of the belt and is a unique phenomenon during the seasonal changes in the East Asian atmospheric circulation at the turn of spring and summer. After mid-June, the rain belt remains in the Yangtze-Huaihe River Basin, which is the Meiyu period. The residence time of the rain belt is called the "Meiyu season". The day at the beginning of the Meiyu season is called "Meiyu season" and the day at the end is called "Meiyu season".