The influence of continuous rain
Continuous rain and humid air are suitable for the growth and reproduction of various molds. In particular, mold lurking on human skin will "resurface", causing tinea pedis, tinea corporis, tinea cruris, tinea manus and tinea versicolor. If not treated in time. Some molds can also grow and reproduce in the human body, causing fungal pneumonia. Some people can cause respiratory allergic symptoms after inhaling mold, such as allergic bronchitis and bronchial asthma, ranging from stuffy nose, runny nose and sneezing to dyspnea and wheezing. Once the disease occurs, it is often difficult to cure, and emphysema or cor pulmonale will form over time. In rainy weather, due to the changeable temperature and high humidity, the conditions of rheumatoid arthritis and rheumatoid arthritis are easy to aggravate or worsen, and pain often occurs in waist strain, sprain, fracture, surgical incision, adjacent joints and other parts. Meteorological factors such as air pressure, temperature and air humidity change greatly in rainy days, which can easily lead to autonomic nerve dysfunction, vasoconstriction, blood flow obstruction, blood pressure increase, myocardial oxygen consumption increase, heart load increase, and even induce cardiovascular and cerebrovascular diseases such as myocardial infarction and stroke. Continuous rainy weather makes people feel depressed. This is because there is less oxygen and more carbon dioxide in rainy days, which inhibits people's respiratory function and blood circulation and slows down people's brain activity.
In rainy and humid environment, food is prone to mildew and deterioration, which can directly or indirectly cause poisoning, vomiting and diarrhea after eating. Eating food contaminated with aflatoxin can also lead to liver cancer and stomach cancer. Continuous rainfall will also cause mildew of grain, feed, grain, clothing, medicinal materials, books, paper and other items, resulting in greater economic losses. Continuous continuous rain will cause continuous cold damage and flood disaster, which will do harm to agricultural production. There may even be a rainy season, and the continuous rainy season has different effects on agriculture, especially in spring and autumn. Continuous rain sometimes leads to wet damage, but more often, due to long-term lack of light, plant photosynthesis is weakened, soil and air are wet for a long time, leading to crop physiological dysfunction, infection and disease, leading to poor growth and development; Continuous rainfall during the grain-filling period of crops will lead to germination and mildew, which will seriously affect the yield and quality of crops. The degree of continuous rainy weather changes greatly every year, which often leads to floods, low temperature, humidity and waterlogging. At the same time, continuous rainfall is easy to induce the occurrence and development of crop diseases and insect pests that like temperature and humidity.
According to the influence of continuous rain on crop growth and development, it can be divided into continuous rain in spring sowing period, continuous rain in flowering period and continuous rain in harvest period.
(1) Continuous rain during spring sowing:
Continuous rainy days during spring sowing mainly occur in the eastern part of China, and in the south of the Yangtze River and South China, they mainly occur at the seedling stage of early rice, often accompanied by low temperature. The middle and lower reaches of the Yangtze River mainly appear in the cotton sowing period. The obvious characteristics of continuous rain in spring sowing date are: long precipitation duration, wide rain area, low rain intensity and poor illumination.
February-March is the early rice sowing and seedling raising season in the southern double-cropping early rice producing areas. At this time, the weather is changeable, winter fashion has a certain intensity, and cold air activities are frequent. When the cold air from the north invades Jiangnan and South China, especially when the cold air from the east of China meets the warm and humid air from the tropical ocean, there are often low temperature, rainy weather and few sunshine at the intersection. At this time, South China and South China successively entered the stage of early rice sowing and seedling raising. The continuous low temperature and rainy weather makes the seedlings lack the heat and light needed for growth, which leads to the rot and death of early rice seedlings. Rainy weather also promotes the propagation and infection of cotton rot fungi in rice fields, indirectly aggravates the degree of rotten seedlings, and leads to a large number of rice seeds loss; It also delayed the sowing season because of replanting, delayed the maturity of early rice, affected the planting of late rice, and then caused low temperature damage during heading and flowering. The frequency of continuous rainy weather during early rice sowing and seedling raising is the highest, followed by warm before and cold after, alternating cold and warm. Late spring cold is the main disastrous weather in the spring sowing and seedling raising period of early rice in southern China, and the low temperature and continuous rain brought by late spring cold weather are the main reasons for the rotten seeds and seedlings of early rice. The results showed that the average temperature on the day of early rice seedling raising was below 65438 02℃, and it rained for 3 ~ 5 days. Or the temperature drops sharply in a short time, and the daily minimum temperature drops below 5℃, which will cause rotten seedlings and dead seedlings. If the rainfall is too large within 1 ~ 2 days after early rice sowing, and there is too much water in the seedling field, rice will not take root easily, and it will also cause rotten seedlings. Feng Peizhi and others analyzed the daily temperature, sunshine and precipitation data of 195 1- 1980 in the sowing period of early rice in Jiangnan and South China, and calculated the cloudy days with sunshine ≤3 hours. The calculation results show that the average cloudy days in the middle and lower reaches of the Yangtze River in recent 30 years are 14 days. The average cloudy day in March in northern South China is 22 days, and the rainy day is about 23 days. According to the temperature change in the same period, the meteorological conditions of early rice seedling raising period were evaluated. In severe low temperature and rainy years, the rot rate of seedlings can reach 30% ~ 40%, and it can reach 60% ~ 70% in severe cases. This kind of bad weather occurred frequently in 1960s and 1970s, and the weather and climate conditions of 1969, 1970 and 1976 were the worst, resulting in serious seedling rot, with the seedling rot rate exceeding 30% and reaching 50% in some years and regions. For example, 1970, the rotten species in Guangxi alone reached more than 50 million Jin; 1976, the average daily temperature in the middle and lower reaches of the Yangtze River was below 12℃ 18 days, and only Hunan, Jiangxi and Hubei provinces lost 300-400 million Jin of rice. 1In the spring of 1996, low temperature and rainy weather lasted for about 20 days again in southern China, which brought great difficulties to rice seedling raising, not only lost a lot of seeds, but also delayed the maturity of early rice due to replanting, which affected the planting and transplanting of late rice and made the heading and flowering period of late rice vulnerable to low temperature. Before and after the three-leaf stage of early rice, when the daily average temperature is lower than 65438 02℃, it will be infected with cotton rot and cause seedling death if it rains for more than three days. At the same time, due to the weak stress resistance when the seedlings enter the second-leaf to third-leaf stage, after low temperature and rainy weather, the sky suddenly clears up, the temperature rises sharply, the daily temperature difference reaches about 10℃, the transpiration of seedlings leaves increases sharply, the root activity is weak, the water absorption and consumption are unbalanced, and the supply exceeds demand, resulting in physiological water loss and green seedlings.
From March to April, the Yangtze River basin entered the spring and began to sow in spring, and the wintering crops entered the critical growth period. Affected by the intersection of the cold air from the north to the south and the warm and humid air from the tropical ocean, "late spring cold" and low temperature and rainy weather often occur in the middle and lower reaches of the Yangtze River and the eastern part of southwest China, which often affect the timely sowing of cotton and cause the epidemic of wheat scab and rape Sclerotinia sclerotiorum. Continuous rainy weather has a great influence on crop sowing and emergence. When the average temperature of that day was 12℃ or below, it rained continuously for 3 ~ 5 days. Or the temperature drops sharply in a short time, and the daily minimum temperature drops below 5℃, which may cause rotten seeds, weak seedlings and dead seedlings of cotton and other crops. Especially, the low-temperature rainy weather with the daily average temperature below 10℃ and lasting for more than 7 days has a particularly significant impact on agricultural production, resulting in low ground temperature, high soil humidity and insufficient sunshine, which weakens the respiration of crop seeds planted underground, hinders their physiological activities and hinders their rooting and germination. Not only a large number of seeds are lost, but also the sowing season is delayed due to replanting, which delays the maturity of crops and affects the agricultural arrangement for one year. If there is low temperature and continuous rain before spring sowing, spring sowing will be postponed; If it appears after sowing, it will lead to rotten seeds and buds, slow emergence and uneven seedling potential; Continuous rainfall after emergence will cause and aggravate the occurrence of crop seedling diseases, slow down the growth of seedlings, and sometimes cause the seedbed to be destroyed and replayed. Therefore, intermittent low temperature and rainy weather often affects the sowing progress of cotton, causing seedling diseases such as cotton seedling blight and anthracnose, which directly affects the emergence rate. Even if it rains in spring, too much rain or poor drainage will cause water accumulation in farmland, causing root rot, premature aging, slow growth and epidemic diseases of wheat and rape. At the jointing stage of winter wheat, when the continuous rainy weather lasts more than 10 days and the soil relative humidity lasts more than 90%, the root system of winter wheat declines and the effective panicle number decreases. For example, in February-March 2000, there were almost no rainy days in most parts of the Yangtze River Basin. It was rainy in most parts of the south of the Yangtze River in February 10 ~ 19, rainy in southeast Sichuan and Guizhou 14 ~ 23, rainy in most parts of the south of the Yangtze River in mid-March 10 ~ 17, with average daily sunshine. After the spring of 2002, the rainfall in most parts of Hubei was nearly 1 times higher than that in the same period in history. Especially from late April to May, the average temperature in most parts dropped below 12℃, which was rare in history and the precipitation was concentrated. In the month from April 22, low temperature was accompanied by continuous rain, during which the precipitation almost reached half of the annual precipitation in Hubei Province, causing serious disasters to Hubei Province. Spring sowing. Cash crops such as vegetables, melons and fruits, and tea have also been greatly affected.
(2) Continuous rainy days in flowering period:
The flowering period of crops is the key stage of yield formation, which is very sensitive to external meteorological conditions and needs suitable temperature and humidity and sufficient illumination. At this time, in case of low temperature and rainy weather, flowering and pollination are blocked, resulting in large-scale "flowering without fruit" of crops, and the seed setting rate is reduced, which has a great impact on yield. Continuous rainy weather mainly occurs in two periods of crop flowering. One is spring, which mainly occurs in the flowering and fruiting period of summer grain and oil crops in the middle and lower reaches of the Yangtze River. Second, in late summer and early autumn, it mainly appears in the flowering period of autumn harvest crops.
In spring, rape and winter wheat in the middle and lower reaches of the Yangtze River successively entered the flowering and pollination period. At this time, cold and warm air often meet frequently in the Yangtze River basin, resulting in low temperature and rainy weather, which affects the flowering and fruiting of rape and wheat. Due to the long duration of continuous rain in spring, the affected area is large. Long-term rainy weather not only causes wet damage, waterlogging damage and even waterlogging damage to crops, but also occurs in the critical period of crop growth in summer, which is likely to have a fatal impact on crops. In southern rapeseed areas, especially in the Yangtze River basin, it is rainy, sunny, rainy and humid from flowering to pod setting, which often causes yin damage and wet damage. The results showed that when the flowering temperature was lower than 10℃, the number of flowers decreased significantly. In case of continuous rainy weather and high humidity of soil and air, it often leads to wet damage, premature senescence of plants and scattered pollen, which significantly affects flowering and fruiting, reduces the number of pods and grains per pod, and leads to yield reduction. The booting stage to flowering stage of wheat is the key period of wet damage, and the recovery ability is the worst and the yield reduction is the most serious after waterlogging. Too much rain, too little sunshine, too much air humidity or too much rain at the flowering stage of wheat will make pollen grains absorb water and swell, which will lead to rupture and death and reduce the seed setting rate. In addition, even rainy weather is easy to induce the occurrence and spread of diseases and pests such as scab, Sclerotinia sclerotiorum and rust, which will have a certain impact on the yield and quality of winter wheat and rape. Continuous rainy weather during the flowering period of wheat, the average daily temperature is above 65438 05℃ and the relative humidity is above 85%, which will cause the outbreak of scab for 3-4 days. Powdery mildew, rust and sheath blight are more likely to occur and spread, causing wet damage, pests and diseases, and seriously affecting the growth and development of wheat.
Rice is very sensitive to light before and after flowering. In the process of young panicle development, if it encounters long-term rainy weather, it will make young panicles stunted. Among them, when the light is insufficient during branching and spikelet differentiation, the number of branches and spikelets decreases; Insufficient light during meiosis and pollen grain filling will cause a large number of branches and spikelets to degenerate, which will increase the number of sterile spikelets, decrease the total number of spikelets, decrease the total number of grains per panicle and decrease the panicle type. Continuous rainfall causes waterlogging disaster at booting stage, which will affect spikelet growth, germ cell formation and pollen development. After differentiation, spikelets will die, branches will degenerate, and a large number of spikelets will be aborted, which has a great impact on yield. In the process of rice flowering and fertilization, when the temperature is lower than 23℃, anther cracking will be affected. The lower the temperature, the greater the impact, and even the inability to pollinate, forming an empty shell. Precipitation has an effect on rice flowering, the number of pollen grains falling on the stigma and pollen germination. Continuous rainfall makes the air humidity too high, which affects the germination of pollen and the elongation of pollen tubes. During precipitation, rice generally does not open glumes, but closes flowers to pollinate; However, if it rains heavily during flowering, the pollen grains will absorb water and burst, and the mucus on the stigma will be washed away, which will reduce the fertilization rate and increase the number of empty shells. During the flowering period of early rice, continuous rain brought by Meiyu front is often encountered. Because of abundant water vapor and strong precipitation intensity, it will form the phenomenon of rain washing flowers, which will lead to reduced production. The continuous rain in late rice flowering is often accompanied by cold dew wind. After mid-September, the temperature was below 20℃ for three consecutive days. Low temperature and rainy weather have a great influence on late rice heading and flowering, which will cause rice ears to tilt up and lead to rice shortage.
Low temperature and continuous rain in autumn not only affect late rice and one-season rice, but also affect the flowering and pollination of corn, cotton and other crops. When it rains continuously in maize flowering period and the relative humidity of air is higher than 90%, the pollen will lose its vitality and even stop flowering; For example, if it rains for several days in a row, the pollen will agglomerate or swell when it meets water, which will reduce the chance of filament pollination and cause a large number of missing grains, bald tips and empty stems; If low temperature and continuous rain occur at the same time, it will delay the spinning of corn, lead to unexpected flowering and form empty stalks. Continuous rain during cotton flowering period will lead to a large number of flowers and buds falling off and reduce the fruit setting rate of peaches. The flowering period of autumn harvest crops in 2003 is a typical rainy year. From mid-August to early September, the Huanghuai and Hanshui river basins experienced cold and rainy weather which was rare in the same period in history. The temperature in central and southern Shaanxi, most of Henan, southwestern Shandong, most of Hubei, northern Anhui, Jiangsu and other major grain and cotton producing areas is obviously lower than normal. The rainy weather lasts for more than 20 days, and the illumination is seriously insufficient. In mid-August, the temperature is 3 ~ 5℃, and the average sunshine time per day. At this time, it is in the period of heading and spinning of summer corn, filling of spring corn, heading, flowering and filling of one-season rice and flowering and bolling of cotton, which is the key period for yield formation. Long-term low temperature, rainy and scanty sunshine make corn pollen absorb water and break, male and female flowers can't bloom, and pollination is blocked, which leads to the increase of bare tip rate of empty stalks, short ears, lack of rows and few grains, and obvious decline in yield. Due to the low temperature and rainy weather, the heading, flowering and filling of mid-season rice and single-season late rice are also seriously affected, and the seed setting rate is obviously reduced. The number of cotton peaches and autumn peaches is small, and the phenomenon of boll dropping and rotten is very serious, and the yield and quality are greatly reduced. According to the field investigation after the disaster, the rate of empty stalks of corn in central and southern Shaanxi and most parts of Henan Province is high, and the rate of bald tips in some areas is over 50%. The phenomenon of missing rows and grains is very common, and the ear length of corn is less than 50% of normal. The peach setting rate of cotton is obviously lower than normal, and some cotton plants hardly bear peaches; The average seed setting rate of mid-season rice in eastern Hubei is only 30% ~ 50%. The total grain output of Henan Province, which was seriously affected by the disaster, decreased by more than 10%, and the total cotton output decreased by more than 40%. Anhui's total grain output and total cotton output decreased by more than 10%. The total grain output in Hubei and Jiangsu decreased by 5% ~ 10%, and the total cotton output decreased by about 5%.
(3) Continuous rain at harvest (rotten rain):
Harvest period is the key stage to determine whether crops can be harvested. If it rains continuously at this time, it will often lead to a large-scale loss of harvest, resulting in a situation of high yield and no harvest. During the harvest period, continuous rainy days mainly occur in the wheat harvest season in late spring and early summer and the corn, cotton and other crops harvest season in autumn, among which the most typical ones are the rotten wheat harvest and the autumn rain in the west.
The occurrence of rotten rain is related to the maturity of wheat and the rainy season. The reason for the rainy weather is the change of atmospheric circulation situation. When the rainy season comes, the cold air in the north supplements to the south and intersects with the warm and humid airflow in the south. The two sides are evenly matched, forming a cloud and rain belt with wide coverage and slow movement, causing a wide range of continuous rain or heavy rain. Because it is in the mature harvest period of wheat, it often causes great losses, ranging from 1 ~ 20% to 350%. Rainfall in wheat rotten fields in Huanghuai area mostly occurs from late May to early June, and the process precipitation is above 50 mm, and rainy days above 0. 1mm and continuous rainy days above 5 days generally occur once every five years. Generally speaking, the summer harvest in the Yangtze River basin is in a relatively dry period before the rainy season, and the wheat harvest can basically be carried out normally. However, the climate in this period changed greatly every year. The subtropical high is strong, the rainy season is early, and the harvest period meets the rainy season early, which will also lead to rotten rain. The average occurrence rate of "rotten wheat field rain" in Jianghuai area is about twice in 10, but it has an increasing trend in the 1990s. The "rotten wheat field rain" appears in 199 1, 1994, 1996 and/kloc-. Even rainy weather will affect the harvesting progress of wheat, and it is difficult to harvest and thresh, the seeds are wet, the respiratory consumption is increased, and the 1000-grain weight and yield are greatly reduced.
The reason for the autumn rain in West China is that from September to June every year, 10, the atmospheric circulation changes from summer to winter. Frequent cold air southward meets warm and humid air stagnant in western China, which intensifies frontal activity and leads to long-term rainfall, thus forming a unique rainy weather phenomenon in autumn in western China. The main areas affected by autumn rain in western China are Weishui River Basin, Hanshui River Basin, and eastern and southern Sichuan Basin, among which eastern and southern Gansu, Guanzhong and southwestern Shaanxi, Chongqing, Sichuan and Guizhou, western Hubei and Hunan, and northeastern Yunnan, among which Sichuan Basin and Guizhou are the most likely areas. The autumn rain in West China is characterized by continuous drizzle. Although there are many rainy days, there is not much rainfall. The autumn rain in West China varies greatly, some years are not obvious, and some years are rainy continuously, as long as 1 month, which has a great influence on agricultural activities such as autumn harvest and autumn planting. Long-term rain and lack of sunshine will adversely affect the harvest and sunshine of corn, rice and cotton. Generally speaking, the longer the continuous rainy process, the greater the harm to crops. The autumn rain in West China has a great influence on the mature harvest of mid-season rice, corn, ratooning rice and other crops, which makes the crops unable to dry after harvest, leading to seed germination and mildew, high yield and poor harvest. The autumn rain in West China prevented cotton bolls from opening, causing peach bolls to rot, which led to a significant reduction in production. Feng Peizhi and others took the days from late August to165438+1early October as a continuous rainy process, and analyzed the autumn rain process in West China at 196 1- 1980. The results show that the 1960s is the frequent period of autumn rain in western China. Then came the early 1950s and the mid-1970s. Since the beginning of 2 1 century, the autumn rains in western China have been frequent and intense. In 2003 and 2005, there was an obvious autumn rain weather in western China, and there was heavy precipitation in continuous rainy days. Autumn floods occurred successively in the Yellow River Basin and the Weishui River Basin, which led to a significant reduction in autumn harvest crops in some areas. From September 26th to June 5438+1October 4th, 2007, continuous rainy weather occurred in the central and eastern northwest, central and southern north China, northern Huanghuai and eastern southwest China. The precipitation in the eastern part of northwest China, south-central North China, north-central Shandong and northeast Sichuan is generally above 50 mm, which is 2-5 times more than normal, and the number of precipitation days is 7-65438 days. Potato tuber rot; Cotton can not be picked normally, and boll rot occurs, which reduces quality and yield.
In addition, in June 165438+ 10, the continuous rainy weather in south China and south China caused late rice to be harvested and aired in time, which led to the germination and mildew of seeds and affected the yield. For example, in June, 2000, there were 1 10 days of continuous rainy weather in parts of south China and eastern South China, which affected the harvesting progress of late rice in some areas. The harvested late rice germinates and lodging, and the harvested late rice becomes moldy without drying.
Mechanisms and causes of disasters:
Several typical continuous rainy disasters in the main growing season of crops have different impacts on agricultural production due to different seasons and regions. Continuous rainy days in spring mainly occur in South China (February-March) and the middle and lower reaches of the Yangtze River (March-April), and often occur at the same time as low temperature weather in late spring. This season coincides with the sowing of early rice seedlings, cotton and other crops, and the production of winter wheat and rape is formed. Low temperature and continuous rain will cause wet damage to rice seedlings, cotton seeds, winter wheat and rape. The continuous rainy days in Meiyu period, which have great influence on agriculture, are early Meiyu and long Meiyu, which often lead to crop waterlogging. The rainy season in early summer is just the flowering and bolling period of cotton in the middle and lower reaches of the Yangtze River. The long rainy season, continuous rain, high temperature and high humidity, and scarce sunshine have led to a large number of cotton buds and bolls falling off. It will also cause the groundwater level to be too high and affect the normal growth of crop roots; Years with heavy rainfall can also lead to floods. For example, in 1954, the extraordinary flood in the Jianghuai Valley of China was caused by unusually long plum rains. That year, there were many spring rains in the second half of May in the middle and lower reaches of the Yangtze River. Meiyu began in early June and didn't "blossom" until early August. The rainy time lasted for more than two months, with occasional heavy rain and heavy rain. The rainfall in the middle and lower reaches of the Yangtze River from May to July is generally 800 ~ 1000 mm, which causes basin-wide floods in the Yangtze River basin and has a serious impact on agriculture. The continuous rainy days during the long plum rain period also adversely affected the booting and filling stages of rice, resulting in the increase of empty grains and the decrease of grain weight. The slow growth of early rice and delayed growth period affect the timely transplanting of late rice. Continuous rain in autumn mainly occurs in the lower reaches of the Yangtze River and southwest China, and the middle and lower reaches of the Yangtze River generally occur in September-65438+10, which can make late rice seeds germinate and rot, and cotton bolls rot and fall off; Autumn rain in western China occurs in Longnan, Guanzhong, southern Shaanxi, western Hubei, western Hunan and most parts of Sichuan and Guizhou, and occurs from late August to mid-10, with September-June to 65438+ 10 as the focus, which often causes lodging, mildew and germination of crops.
In addition, continuous rain (snow) in winter mainly occurs in winter wheat and rape producing areas in the middle and lower reaches of the Yangtze River. Due to continuous rainfall, insufficient sunshine hours, high humidity in the field, low ground temperature, long-term saturation of soil water content, lack of oxygen in crop roots, inhibition of respiration, decline in vitality, and decline in water and fertilizer absorption capacity, organic substances in the soil produce reductive toxic substances to poison the roots under anaerobic conditions, resulting in poor root growth and reduced root mass; It also reduces nitrogen metabolism in plants, and the nitrogen content in functional leaves is obviously reduced, resulting in yellowing or stiff seedlings. For example, on June 5438+0, 2006 and February/kloc-0, 2002, there was a large-scale continuous rainy (snowy) weather in Jianghuai, Jianghan, Jiangnan and the eastern part of Southwest China, with few rainy days. Among them, in June 5438+February, 2002, the cumulative number of rainy (snowy) days in Jianghuai, Jianghan, Jiangnan and Southwest China reached 13 ~ 20 days, the monthly sunshine hours in most areas were only 30 ~ 80 hours, the precipitation was more than 13 times than normal, the relative humidity of farmland soil exceeded 90%, and some areas were low-lying. In North China, Huanghuai and other places, there will be persistent rainy (snowy) weather in winter, which has a great impact on the growth and development of greenhouse vegetables and causes greenhouse vegetable diseases. At the same time, due to the frequent coverage of snow or plastic film on rainy (snowy) days, the temperature in the greenhouse has dropped slightly. However, after the snow is cleared or covered with plastic film, it often turns fine after continuous rain (snow). At this time, the strong cold air is controlled, the radiation cooling at night is enhanced, the greenhouse temperature is greatly reduced, and vegetables are prone to chilling injury or freezing injury, leading to wilting or rapid withering and death.
In addition, due to continuous rainfall and excessive humidity, some crop diseases and insect pests will occur and spread. Continuous rain often occurs in spring in southern China, autumn in Jianghuai area, late spring and early summer in North China Plain and autumn in South China. For example, in early June of 1989, continuous rainy weather occurred in most parts of North China Plain, which caused mildew and germination of wheat at harvest time and caused huge losses.
Disaster index:
The process of continuous rain is related to precipitation, sunshine and low temperature, and the harm to agriculture is mainly floods caused by continuous rain, too little sunshine and continuous low temperature. The damage degree of continuous rain varies with season, duration, temperature, previous rainfall, crop species and growth period. Sometimes, due to long-term rainy weather and a large amount of accumulated rainfall, water accumulated on the ground, too much water in the cultivated layer for a long time, crop root rot or the spread of pests and diseases, resulting in waterlogging, and serious spring waterlogging affects the timely sowing of crops and the growth of crops in summer. It rains continuously in the middle and lower reaches of the Yangtze River in spring. Due to insufficient light, three wheat waterlogging and cottonseed rot will occur. Continuous rainy days in the south of the Yangtze River in spring are unfavorable to rice seedling raising and easy to rot. In addition, the isothermal crops of cotton and peanut often cause rotten seeds and dead seedlings; It also affects the flowering and pollination of rape, abnormal pod development and reduced yield; Sometimes it will affect the booting stage of wheat, leading to large-scale infertility or poor fruit quality. In the harvest season, continuous rain will cause germination mildew of rape, barley, rice and peanuts, cotton boll rot and petal stiffness, and sweet potato rot. Continuous rainfall in early summer and autumn is not conducive to summer harvest and autumn harvest, and grains are not easy to dry in the sun but easy to germinate and rot. Although continuous rain and its combination with season, temperature conditions and precipitation intensity often produce different hazards, it is characterized by more rain and less sunshine. Therefore, the indicators of continuous rainy days often include rainy days and sunshine. Generally, it is divided into seasonal continuous rainy days according to the occurrence time, in which March-May is spring continuous rainy days, June-August is summer continuous rainy days, and September-165438+1October is autumn continuous rainy days. Wu Hongyan and others defined March 1 day to May 3 1 day as the occurrence time of continuous rain in the middle and lower reaches of the Yangtze River in spring, and adopted the continuous rain criteria as follows: ① the continuous rain period with daily precipitation of more than 7 days ≥ 0.1mm; ② The proportion of days with daily precipitation ≥0. 1mm to total days ≥70%, sunshine hours in rainy days < 5 hours, and total precipitation ≥10 mm; (3) If it doesn't rain for three consecutive days, it will be regarded as the end of continuous rain. Satisfying ① or ② is continuous rain. Based on the above criteria, the continuous rainy days in spring 196 1- 1999 in Jiangsu province were statistically analyzed. The results show that the cumulative number of continuous rainy days and total precipitation in spring are negatively correlated with summer grain yield. When the cumulative number of continuous rainy days is ≥30, the summer grain yield is very obvious, and the probability of this situation is 59.438+0%.
Due to the different climate and crop layout, the continuous rain index formulated by different places according to local weather and climate conditions and crop growth and development laws is slightly different. For example, the continuous rainy day index in Gansu in the western part of the Loess Plateau is ≥5 days, and the process precipitation is ≥ 15mm (1 day with little or no precipitation is allowed, but the precipitation on the start or end day of the process must be ≥ 0.1mm); The average daily total cloud cover is ≥ 80%. It is a continuous rainy weather process that meets the above conditions. There will be three or more consecutive days of precipitation (daily precipitation ≥0. 1mm, excluding fog, dew and frost) in Anhui in Jianghuai area, which is a continuous rainy (snowy) process; In the process of continuous rain (snow) for more than 3 days, one day without precipitation is allowed, but the sunshine on that day is less than 2 hours; In the process of continuous rainfall (snow), a small amount of precipitation is allowed, but the sunshine on that day
According to different farming seasons and stages, there are different definitions of continuous rain in different places. For example, in Beijing, Tianjin and other places, wheat is close to maturity, with continuous precipitation for 3 days or more and total precipitation ≥40mm during the harvest period, which is regarded as an indicator of continuous rain in wheat harvest, and it is divided into light and heavy according to the number of days. Among them, the weight: during the continuous rainy season, the sunshine hours for 3 days or more are ≤6 hours; Illumination: the sunshine hours for two consecutive days in the process of 65438+ are ≤6 hours. Anhui, on the other hand, defines the "rotten rain" index of summer harvest from late May to mid-June as: continuous rainy days ≥5 days in a rainfall process, and the process precipitation is above 50mm; At the same time, if the number of rainy days is less than or equal to 4 days, but the process precipitation is relatively large (at least 1 rainstorm day), which causes serious floods and losses to wheat, it is also counted as "rotten field rain". In Shaanxi, continuous rain in autumn is called autumn rain. It is stipulated that from late August to 65438+1mid-October, the daily precipitation is ≥0. 1mm, the continuous rainy days are ≥4 days, and the total precipitation is ≥20mm, which is a continuous rainy process. Considering the duration, frequency and total precipitation of continuous rain in autumn, it can be divided into weak autumn rain, medium autumn rain and strong autumn rain. There are 1 ~ 2 short-term continuous rainy processes in autumn, and the total precipitation is ≤40mm, which is a weak autumn shower; There are ≤2 moderate continuous rainy processes in autumn, 40 mm; 80mm is a strong autumn rain.