What is the relationship between the intensity of summer monsoon and the flood disaster in Huaihe River?

Drought and flood are the most extensive and harmful natural disasters in our province. The causes of drought and flood are very complicated, which are related to climate, geographical conditions, water conservancy facilities, soil structure, crop layout and their ability to resist drought and flood at different growth stages. Precipitation is the main factor of drought and flood, and the disaster situation and severity are closely related to water conservancy facilities.

Due to the specific geographical location and terrain. The characteristics of drought and flood disasters in our province are: frequent occurrence, serious harm, interwoven drought and flood, drought greater than flood, flood greater than drought.

I. Overview of Floods Floods are caused by the concentration and intensity of precipitation. Generally speaking, the daily precipitation is ≥ 200mm, or the precipitation is ≥ 300mm in 2-3 days. No matter what other conditions, there will be waterlogging. The longer the duration of heavy precipitation, the larger the coverage and the more serious the flood. Floods mainly occur in the flood season, and the rainy season is the most frequent. Waterlogging will also occur in spring and autumn, which is generally called waterlogging or waterlogging. Waterlogging in spring is mainly due to long-term continuous rainfall, which leads to water accumulation in the field and affects the later growth of wheat and rape. The western Yangtze River, Lu 'an, Lujiang, southern Huaibei and areas along the Huaihe River between Jianghuai are frequent areas. Spring waterlogging mainly occurs from late April to May in Anqing, west of the Yangtze River, and May is one of the worst waterlogging periods in the whole year. However, the possibility of a big flood in spring in our province is very small, and it has basically never happened in most areas between Jianghuai and eastern Jiangnan. There is little waterlogging in autumn around the country. Comparatively speaking, Suxian, Sixian, Bengbu and other places along Huaibei and the eastern part of Huaihe River appear more frequently. Since 1980s, autumn waterlogging has been frequent. From the end of 1996 to116, there were continuous rainy days in our province 19 days, and the heavy precipitation center was located along the Huaihe River on1October 30th, 30th and 60th respectively. 1October 7th 165438+ The water level of Wangjiaba exceeded the warning level, and the highest water level of 28.60m appeared at 7: 00 on 10 (only 6cm away from the guaranteed water level in flood season), which is an autumn flood once in 50 years. Near winter, tens of thousands of people went to the embankment to prevent floods, which is the first time in the history of Huaihe River flood control.

Summer waterlogging is the most prone to occur in a year, especially large waterlogging and extra-large waterlogging, mainly concentrated in summer. The summer waterlogging time advances from south to north, along the south of the Yangtze River from mid-June to mid-July, between the Yangtze River and Huaihe River in July, and from July to August, which is consistent with the movement of the main rain belt from south to north in the flood season in eastern China. The waterlogging-prone areas are mainly Anqing along the Huaihe River and west of the Yangtze River. Hefei is the area with the least flood disaster. The major waterlogging and extraordinarily serious waterlogging in the whole province occur once every 5 years/kloc-0. Since 1950s, there have been 1954, 1969, 19 1 and 1996 in the whole province. The probability of waterlogging in each natural area is once every 3-4 years along the south of Huaihe River and Yangtze River, and once every 2-3 years along the west of Yangtze River. Most areas between Jianghuai and northern Huaibei and Xuanlangguang meet once every 4-6 years; 9- 10 Central Jianghuai once; Hefei10-15 once. There are obvious differences in precipitation between windward slope and leeward slope in mountainous areas. In addition, the mountains are high and the valleys are deep, the water flows quickly, and mountain torrents often occur, so the probability of waterlogging is greater. However, the flood generally lasts for a short time and has a small influence range.

Second, the causes of floods

The main reason for the serious waterlogging in our province is the abnormal plum rain. Several severe floods in our province were caused by extremely long meiyu period, extremely large amount of meiyu, concentrated precipitation, frequent and large-scale rainstorms.

The abnormal circulation conditions of Meiyu are: the situation over Asia and the northwest Pacific is relatively stable, and the air over our province has been in a cold and warm air confrontation area for a long time. It shows that the intensity and ridge line of the subtropical high in the western Pacific remain at the best intensity and position for transporting water vapor to our province for a long time (the ridge line is about18-25 N, and the western ridge point is about100-120 E). The blocking high is often maintained at the middle and high latitudes in Asia, and the meridional circulation is significant; The mid-latitude circulation is relatively gentle, and there is no strong cold air invading south, and small fluctuations frequently move eastward to affect our province. In this situation, Meiyu front has been at rest or swinging in the middle and lower reaches of the Yangtze River for a long time, and the low-pressure disturbance has been spreading eastward. During the eastward movement of the upper trough, for example, the low-altitude southwest wind in Hunan, Hubei and western Jiangxi is often above 65438 0.2 m/s, and the airflow convergence in front of the jet center is relatively strong, which is most likely to trigger a sub-weather scale system in the Jianghuai Basin, thus causing heavy rain or heavy rain. When this circulation situation is stable for a long time, the corresponding rain belt is also stable in the Jianghuai basin, resulting in a large-scale and long-lasting serious flood disaster in our province. For example, 1954, 199 1, 1996.

Another reason for waterlogging in our province is that the typhoon depression goes deep into our province, and it can't be moved out smoothly under the specific circulation situation, but the moving speed slows down or even stops rotating, and there is weak cold air moving south in the north. Coupled with the superposition of weather systems of various scales and the influence of topography, very strong rainstorms can occur in some places. The rainstorm with daily rainfall of more than 400 mm in our province is mostly caused by typhoon depression, which causes serious local waterlogging. For example, Typhoon 7504 caused serious waterlogging in Chuxian, Lai 'an and Jiashan.

Three. flood

The severity of flood disaster is related to local topography, landform, water conservancy facilities and crop growing season, and the economic losses caused are also directly related to local economic development. The worst floods in our province are 1954, 1969, 199 1, 1996.

On June 4th 1954, the plum rains lasted for 57 days on July 30th. During the Meiyu period, there were many heavy rains, heavy rainfall and a wide range, and there was a once-in-a-century flood. Total precipitation from May to July: Jianghuai to Wuhu is 900- 1300mm, Dabie Mountain, Anqing, Chizhou and Huizhou 1300-2000mm, with some exceeding 2000mm. Due to the long time and intensity of precipitation, the river water level soared. The water levels in Anqing and Wuhu sections of the Yangtze River exceeded the historical highest water level (193 1 year) and exceeded the warning water level 100 days. Along the Huaihe River, Huaibei entered the rainy season in early July and ended in late August, lasting nearly two months. The length of the rainy season and the amount of rainfall are unprecedented in previous years. The total precipitation in July and August is generally 600- 1000mm, and that in Suxian County is1100 mm.. The highest water level has appeared in all sections of the main stream of Huaihe River, and the highest water levels in Zhengyangguan and Bengbu have partially exceeded the historical highest water level. Extraordinary floods occurred in the Yangtze River and Huaihe River basins. Many areas along the Yangtze River, Huaihe River and its tributaries burst their banks, resulting in waterlogging, flooded farmland and serious losses in industrial and agricultural production. According to statistics, the affected population150,000, the affected farmland was 45.73 million mu, the grain output was reduced by 3.9 billion Jin, and 2,843 people died.

199 1 year, our province once again suffered from the worst flood disaster in a century. 1991May 18 entered Mei, and rose to Mei in July 12. The rainy period lasted for 56 days, only one day less than 1954. Meiyu is divided into two sections: the first section (May1August-June 20th), with eight heavy precipitation processes, and the number of regional rainstorm days16; In the second phase (June 29th-July 12), there were eight heavy precipitation processes, with large-scale rainstorm days *** 13. The intensity of rainstorm is high and the rainfall is fierce. The number of rainstorm days with daily rainfall ≥ 100 mm is *** 10, 4 days more than 1954; There were ***5 large-scale rainstorms, covering more than 10 counties and cities, with the maximum range exceeding 15 counties and cities. In the 56 days from May 18 to July 12, the area with rainfall exceeding 500mm in the whole province is 1 16000 square kilometers (63 counties and cities), and the area with rainfall exceeding 800mm is 77000 square kilometers (43 counties and cities) with about 23000. The total rainfall from May to July is 600- 1300mm in most parts of the province, and 900- 1300mm along the Huaihe River, except for a few areas in the north of Huaibei, where floods are the most serious. The flood of 199 1 is different from that of 1954, and the flood center is along the Huaihe River. Long-term and large-scale heavy rainfall caused the water level of the main stream of the Huaihe River, lakes and depressions along the Huaihe River, tributaries on both sides of the river, Chuhe River, Chaohu Lake and large, medium and small reservoirs in the Yangtze River basin to skyrocket. The continuous floods in Huaihe River and Chuhe River exceeded or approached the historical record. Of the 65,438+00 large reservoirs in the province, 7 have the highest water level since the station was built. The main stream of the Yangtze River has exceeded the warning water level, and the Chaohu sluice has the highest water level since it was built. There have been three consecutive flood peaks in the main stream of Huaihe River, and 22 flood storage and detention areas along Huaihe River have been opened one after another, 15. The main tributaries and lakes of Huaihe River have experienced the biggest floods since the founding of the People's Republic of China, and 16 small and medium-sized rivers have the highest water levels since the founding of the People's Republic of China. The maximum stagnant reservoir capacity along the Huaihe River Valley is 8.2 billion cubic meters. From mid-June to mid-July, the Chuhe River suffered two extraordinary floods, both exceeding the highest water level in history. The history of waterlogging in Chaohu Lake is rare. The normal surface of Chaohu Lake is 778 square kilometers. Because most of the dikes along the lake burst, the lake surface increased to 1240 square kilometers. 199 1 another feature of the flood is that the rainy season comes very early and cannot be prevented. On May 18, there was a rainstorm in the whole province. The rainy season south of Huaihe River is nearly one month ahead of schedule, and the rainy season in Huaibei is 40-50 days ahead of schedule. From the end of May to the middle of June, it is the mature harvest period of rape and wheat in our province. Sudden heavy rainfall prevented most wheat harvesting areas from harvesting in time, resulting in serious yield reduction or even no harvest. According to statistics, the affected area of 199 1 summer and autumn crops is 87,594,300 mu, of which 80,086,800 mu will be lost and 27,920 mu will be lost. In the whole year, the grain output was reduced by/kloc-0.09 billion kg, the affected population was 43 147 million, and 92.27 million people died.

1996 is another catastrophic flood disaster year after 199 1 year. Its severity is second only to 1954 and 199 1 year. On June 2nd 1996, the plum rains entered Mei, and on July 22nd, the plum rains lasted for 50 days. This is the third long rainy year since the 1950s. Meiyu can be divided into three sections, namely June 2-1 1, June 15-20, and June 23-July 22. 1996 Meiyu is characterized by unstable rain belt, which swings repeatedly in our province from south to north, wide coverage of rainstorm and heavy rainstorm, and more regional rainstorm and rainstorm days. In June, the rainstorm was mainly concentrated in the western part of the Yangtze River and the south of the Yangtze River, and in July, the rainstorm was mainly concentrated in Dabie Mountain area and the western part of the Yangtze River. Regional rainstorms are mainly in the south of the Yangtze River, the west along the Yangtze River and Huaibei. Meiyu amount is 1996: 400-800 mm in Jiangbei and eastern Jiangnan, Dabie Mountain area and along the river. Southern Jiangnan1000-1800 mm. Among them, most counties and cities along the Yangtze River in the west and Jiangnan exceed 1954 and 19 1 year, and Dabie Mountain exceeds 1954. Frequent rainstorms and extremely heavy rainstorms repeatedly swept across the north and south of our province during the meiyu period of more than 50 days, causing waterlogging disasters in most parts of the province, among which southern Jiangnan, Dabie Mountain area and Huaibei Su County were the hardest hit areas, and Wangjiaba, the main stream of Huaihe River, had three flood peaks. According to statistics, 40 of the 68 counties and cities in the province were affected to varying degrees, 15 counties and cities were flooded, with 773,600 hectares of flooded farmland, 1 1.73 million hectares of crops,10.25 million people affected, and10.05 million people died.

Since ancient times, floods have been the greatest threat to mankind, and catastrophic floods often cause serious floods. According to the statistics of the United Nations disaster relief department, the losses and casualties caused by floods rank first among 15 natural disasters. Our province is located in the transition zone between north and south climate, and often stays in the main rain belt in summer. In most years, there are waterlogging and floods to varying degrees, which bring harm to people's lives and property and industrial and agricultural production.

The fourth quarter drought disaster

I. Overview of Drought The drought in our province is mainly caused by the lack of long-term precipitation, which may occur all year round. Spring drought, more in the north, less in the south, rarely occurs in the Yangtze River and Jiangnan area; The northern part of Huaibei is the most prone to severe spring drought in our province, and the frequency of drought is higher than that of summer drought. Summer drought is less in mountainous areas and northern Huaibei, and it is more likely to occur in other areas, but severe summer drought is most common in southern Huaibei, along Huaihe River and northern Jianghuai. The whole province is prone to autumn drought. Relatively speaking, severe autumn drought is most likely to occur in the mountainous areas of Jiangnan and southern Anhui. Winter drought is most likely to occur in the north of Huaibei, at least in the south along the river between Jiangnan and Jianghuai. Drought mainly affects crops directly, so summer drought is the most harmful. Summer drought is mainly caused by the lack of plum rains, and the once-in-a-century severe drought is closely related to the extremely short empty plum blossom or plum blossom period and the unusually few plum rains. Drought often occurs in successive seasons, such as summer and autumn drought, winter and spring drought and even four seasons drought. Drought has been a serious situation for several years. For example, in the 1960s, from 1966 to 1968, most parts of the province suffered from severe drought for three consecutive years. The 1960s was the most frequent period of drought in our province, and it was aggravated in 1990s. The opportunity of drought in most areas of the province comes once every 2-3 years, once every 2 years in northern Huaibei, once every 3-4 years in Dabie Mountain area and eastern Jiangnan, and once every 5 years in severe drought in the province. The frequency of drought is much greater than that of waterlogging years. Except for a few years, there are drought areas in our province almost every year. Even in flood years, such as 1954, 199 1, after the rainy season, severe autumn drought occurs. Since 1950s, severe drought years such as 1966, 1978 and 1994 have occurred in the whole province.

Second, the characteristics of circulation in drought period

The dry weather conditions are different in each season. The characteristics of 500 HPA circulation that causes the persistent drought in summer in our province can be summarized into three categories:

1, the westward extension of subtropical high controls our province;

2. The eastward movement of continental high pressure controls our province;

3. The eastward movement of continental high and the merger of subtropical high form an east-west zonal high that controls our province.

Under the control of subtropical high, a warm air mass prevails in the downdraft, and there is an obvious inversion layer in the middle and lower troposphere, so the weather is sunny and hot under the control of subtropical high. When it is maintained in a certain area for a long time, it will cause drought. One case is that the subtropical high is located in the south in early summer, the warm and humid airflow in the southwest meets the cold air in the north from South China to Jiangnan, and the main rain belt is located in the area from South China to Jiangnan. Due to the stability of subtropical high, it was too late to jump northward, and Jianghuai entered Mei late. Once the subtropical high jumps northward, it extends westward again, quickly completing the second seasonal northward jump. The corresponding main rain belt only stays in Jianghuai area for a short time, and then quickly moves to Huanghuai and even North China. The empty plum or plum rain period in our province is very short. After that, our province was controlled by subtropical high, and it was sunny and hot with little rain, which led to summer drought. The longer the subtropical high is controlled, the heavier the drought will be. On the other hand, in summer, the subtropical high is obviously weak, oval in distribution and abnormally eastward. A trough of low pressure is often maintained along the coast of East China. The Jianghuai basin is controlled by the northwest airflow behind the trough, and there is no obvious blocking high pressure in Siberia, Hubei and the middle and high latitudes. In this case, the weather in our province is sunny and rainy, and there is no obvious high temperature and heat. Sometimes, with the subtropical high temporarily extending westward, process precipitation often occurs. In this case, the duration of drought is relatively short and the harm is light.

Three. Drought disaster

Drought is caused by the circulation system with large scale in time and space, and it is a slow and intensified process, which directly harms crops. The harm caused by drought is closely related to the growing season of crops, especially the "neck drought" at the booting stage of crops. Crops are most sensitive to water at booting stage. In case of drought, the reproductive organs of crops are often stunted, and the empty grains increase obviously, resulting in a sharp reduction in grain production. As for the drought for several months, seasons or even years, the water level of rivers has dropped, the ponds of rivers, lakes, reservoirs have dried up, agricultural irrigation has no water available, farmland has cracked, crops have died, and grain and oil production has been greatly reduced. What's more, it is difficult for people and animals to drink water in rural areas, and industrial water and urban water are limited, which will also bring a series of social and economic problems, which are no less harmful than floods. Several severe droughts in our province have caused great harm.

1978 is a rare drought year in the history of our province. Since mid-March, it seldom rains every month, and the drought continues to develop, covering the whole province. The severity and scope of this disaster have never been seen in a hundred years. Annual rainfall in the whole province: along the Huaihe River, most areas between Huaihe River and Jianghuai River, Wuhu area is 400-700 mm, and Dangshan, Jingxian, Dabie Mountain and Anqing, Chizhou and Huizhou areas are 700- 1 100 mm. Compared with the average over the years, except for Dangshan, which is more than 1%, the rest areas are less than 30%-50%, and Bengbu, Shouxian and Wuhu are less than half of the normal ones. The rainfall during the year 1 and February is relatively normal. Since mid-March, there has been little rain in the Huaihe River and Huaibei, and the spring drought is serious. At this time, the growth of overwintering crops needs a lot of water, and severe drought will have a great impact on the yield of wheat and rape, and spring sowing crops are difficult to sow or emerge unevenly. There is less rainfall and obvious drought in most areas between the Yangtze River and Huaihe River, which makes rice planting difficult. The water along the Yangtze River in Jiang Nanyu is still well mixed. In summer, our province is often controlled by weak cold and high pressure, with little rain on sunny days. Until the end of June, the subtropical high moved rapidly northward over the south of the Yangtze River, and the rain area moved northward. From 23rd to 25th, there was a heavy rain between the Yangtze River and Huaihe River. After the rain, the subtropical high quickly controlled East China, and the weather was sunny and hot, forming an "empty plum". Our province entered the midsummer half a month ahead of schedule, and the drought spread rapidly throughout the province. From June to July, the rainfall along the Yangtze River was only about 30% of normal, and the rainfall in Wuhu, Anqing and Tunxi was less than 100 mm in two months, which was the lowest since the historical record. From June to August, the rainfall in the south of Huaihe River is mostly less than 200mm, but the evaporation is as high as 600-800mm, which is four times of the precipitation, and the drought is greatly aggravated. In midsummer, there is no typhoon affecting our province. On the contrary, after several typhoons turned, the continental high quickly strengthened eastward and merged with the subtropical high to control our province. Every time there is hot and dry weather of about 10 days, which makes the drought more and more serious, especially in the south of Huaihe River. 65438+ 10 September-June is still mainly sunny, with scarce precipitation and severe autumn drought, which affects the sowing and emergence of autumn sowing crops. In June, there was more rainfall in 5438+065438+ 10, and the drought in some areas was slightly alleviated. From June to February, 5438, the whole province was controlled by high pressure and the drought continued. 1978, Huaibei is a spring drought; Summer drought plus winter drought, summer, autumn and winter drought in the Yangtze River and Jiangnan; There is a continuous drought between the Yangtze River and Huaihe River from spring to winter. Due to less continuous precipitation, high temperature and large evaporation, except in low-lying areas along the river and lake, ponds in many places have dried up and water sources are thirsty. The large reservoir has bottomed out, and there is no water to put in. The water level of the Yangtze River plummeted, culverts were cut off, and large areas of farmland were cracked. Due to lack of water, most crops die in autumn, and crops such as rice and cotton are greatly reduced due to drought. It is extremely difficult for people and animals to drink water in a considerable number of counties and cities in this province.

Since 1994, a serious drought has occurred in our province, which is second only to 1978. There are droughts in Huaibei in spring and summer. The summer drought in the whole province is the worst year since the 1950s, and there are two short-term droughts in autumn. June 6 1994, affected by the rain belt in South China, the southern part of the south of the Yangtze River in our province entered Mei. May, June 28th. Meiyu mainly falls in the south of the Yangtze River, and the area between Yangtze River and Jianghuai is mainly affected by cold air from north to south. It is a process of precipitation, and it is really "empty plum". After plum blossom, there is less precipitation, high temperature and heat, large evaporation, and the soil moisture content drops sharply. The drought in Jiangbei area develops rapidly, especially in Huaibei area. By mid-July, the drought-affected area in the province was 4 1 10,000 mu, with 24.3 million mu seriously affected and nearly one million mu of dead seedlings. /kloc-since July 0/2, there has been a large-scale rainfall in the whole province, and the drought has been alleviated for a time. Since late July, there has been another hot and muggy weather in our province, and the drought in the eastern part of our province has become increasingly serious. In Chuxian, Hefei, Chaohu, Xuancheng and other areas, some small ponds and reservoirs dried up, and the fields cracked, making it difficult for people and animals to drink water. In August, the precipitation in the whole province was scarce and the drought continued to develop. By mid-August, the drought-affected area of crops in the province reached 49.45 million mu, accounting for 78% of the local crops, and the affected area was 35.9 million mu, of which12.66 million mu was seriously affected and the basic loss12.58 million mu. Six million people were affected, accounting for 75% of the province's agricultural population. The number of people suffering from various diseases caused by high temperature is 6.5438+0.65438+0.2 million, 5.2 million and 65.438+0.70 billion, and the direct economic loss due to the disaster is 65.438+0.10.70 billion yuan.

The following table is 1953- 1996 drought and flood grade statistics in our province. * * It is divided into five grades, 1 grade is severe drought, grade 2 is partial drought, grade 3 is normal, grade 4 is partial waterlogging, and grade 5 is severe waterlogging (standards and statistical tables are provided by provincial climate center).

1953 ——1996 Statistics of drought and flood grades

Huaibei Jianghuai Dabie Mountain along the Yangtze River Jiangnan Year Huaibei Jianghuai Dabie Mountain along the Yangtze River Jiangnan

1953 1 2 3 3 1975 3 5 5 3 4

1954 5 5 5 5 1976 1 1 1 2 2

1955 3 2 3 3 1977 3 4 5 5 5

1956 5 4 4 4 1978 1 1 1 1 1

1957 3 3 2 3 4 1979 4 3 3 3 1

1958 3 2 3 2 1 1980 3 3 3 5 5

1959 2 3 3 3 3 198 1 2 3 4 4 4

1960 3 3 3 3 3 1982 3 3 2 3 2

196 1 2 2 3 2 3 1983 3 4 5 5 5

1962 3 3 2 3 1 1984 4 3 3 3 3

1963 5 3 3 2 1 1985 3 3 3 2 2

1964 4 3 3 3 2 1986 2 2 3 3 3

1965 4 2 1 3 3 1987 3 5 4 3 3

1966 1 1 1 1 3 1988 2 2 3 2 1

1967 3 1 2 2 2 1989 3 4 4 4 5

1968 3 2 1 1 1 1990 3 2 3 3 3

1969 3 4 5 4 3 199 1 5 5 5 5 4

1970 3 3 3 4 4 1992 2 2 1 2 2

197 1 3 3 2 2 3 1993 2 4 3 3 5

1972 3 4 3 3 3 1994 1 1 2 1 1

1973 2 2 4 4 5 1995 3 1 1 3 4

1974 4 4 3 3 3 1996 5 4 5 5 5

Section 5 Changes of Climate Resources and Their Impact on Agriculture

The change of climate and agricultural climate resources has great influence on agricultural production. Studying the changing law of agricultural climate resources and its influence on agricultural production is an important reference for agricultural production to avoid disadvantages and long-term planning, so many experts and scholars are very concerned about climate change and its influence. According to the research of the provincial agricultural gas center (the change of agricultural climate resources in Anhui in recent 40 years and its influence on agriculture, disaster reduction and development, 2 1997), Anhui was cold in the 1950s, but it was rich in light and water resources. There was little rain in the sixties and seventies, and the collocation of light and hot water was not reasonable. In the 1980s, the temperature was low, the winter was warm and the summer was cool, and the climate productivity was low, but the combination of light and heat was good.

I. Variation characteristics of temperature and heat conditions

1, temperature change

The annual average temperatures in Huaibei, southern Anhui and western Anhui are 14 ~ 15℃, between Jianghuai and Jiangnan,16℃ and 17℃, with an annual average temperature of 0.0 ~/kloc-0. The basic characteristics of the annual average temperature change in the province in recent 40 years are as follows: in 1950s (1953- 1960), it was 0. 19℃ lower than the historical average, and in 1960s (1-1). The temperature changes obviously in different years in summer. In the 1960s, the temperature was 0.45℃ higher than the average over the years, and in the 1980s, the temperature was 0.42℃ lower, indicating that the cooling trend in the 1980s was obvious. The winter temperature is the lowest in 1950s, warmer in 1970s and warmer in 1980s, but the difference with the historical average is very small. The spring and autumn of 1950s was low, and there was no obvious difference in other decades.

2. Changes in thermal conditions

Besides temperature, there are accumulated temperature, frost-free period, ≥0℃ and? Days at 0℃, etc. The interannual fluctuation of accumulated temperature is one of the main factors that cause the change of agricultural climate resources. The boundary temperatures of 0℃, 5℃ and 10℃ can represent the available heat conditions of agricultural activity period, crop growth period and thermophilic crop growth period respectively. The daily variation range of accumulated temperature ≥0℃ in Anhui Province is 565,438+000 ~ 665,438+000℃, and the annual fluctuation range is 500 ~ 700℃. There was a big interannual fluctuation in the 1950s, and the accumulated temperature anomaly was positive from the end of 1950s to the end of 1960s, and the accumulated temperature decreased year by year from the end of 1960s to the middle of 1970s, indicating that the thermal conditions became worse during this period. At the end of 1970s, the accumulated temperature was higher than the historical average. In the 1980s, due to the cooling in summer, the high temperature time was shortened, resulting in insufficient accumulated temperature. The annual fluctuation of accumulated temperature ≥ 10℃ is different from that of accumulated temperature ≥0℃ and ≥5℃, which was less before 1960s, more in 1970s and relatively less in 1980s. The interannual variation of accumulated temperature in different seasons is as follows: the accumulated temperature is ≥0℃ in summer (June-August), and it gradually decreases between Huaibei and Jianghuai after the early 1970s, and it is less than the historical average almost every year in 1980s; The accumulated temperature in Jiangnan area decreased slightly, but it also showed a downward trend. The accumulated temperature in winter, spring and autumn was obviously less in 1950s, more in 1960s and 1970s, and more in 1980s. It shows that it is warm in winter and cool in summer since 1980s, and this trend is obvious between Huaibei and Jianghuai.

Days ≥0℃, frost-free period and? The number of days at 0℃ is also an important indicator to reflect the heat status of a region. Statistical analysis shows that the days of 0℃ and frost-free period in Anhui province in 1950s and 1970s are 6-9 days shorter than those in previous years, which is not suitable for agricultural activities? The number of days at 0℃ is 5 ~ 7 days more; The sixties and eighties? The days of 0℃ and frost-free period have been extended, but in the 1980s? The average extension of days at 0℃ 1 1 day. It shows that although the accumulated temperature was insufficient in 1980s, the growing season of crops became longer, and the decrease of accumulated temperature was mainly caused by the decrease of temperature intensity. In the 1980s, the winter cold season was shortened, which was beneficial to agricultural production and crops overwintering.

Second, the characteristics of precipitation and drought and flood changes

1, the change of annual precipitation

The annual total precipitation in Anhui province fluctuates greatly in different years, and the difference between the precipitation in 1954 with severe waterlogging and that in 1978 with severe drought is nearly three times. Over the past 40 years, the whole province has experienced a rainy period in the 1950s, a dry period with little rain in the 1960s and 1970s and a rainy period in the 1980s. In 1950s, the annual precipitation was nearly 100 mm more than the average of previous years; 60-70 mm less in the sixties and seventies; About 60-70mm more in the 1980s. In terms of geographical distribution, the rainfall in the north (along Huaihe River and Huaibei River) began to be less in the late 1960s, and the south (south of Jianghuai River and its south) began to enter a rainy period in the early 1980s. The interannual fluctuation of precipitation in different seasons is also quite large. The interannual variation trend of summer (June-August) precipitation and annual precipitation is basically the same, but the regional distribution is different. Since the 1970s, there has been little rain in summer in the north, while the rain in the south has gradually increased. It was rainy in winter in the fifties and seventies, but less in the sixties and eighties. Since 1980s, there has been an obvious trend of less precipitation in spring and an increase in autumn.

2. Drought and flood changes

Anhui province is a drought-prone area, with an average of 2-3 years of drought and flood, and 4-5 years of drought and flood in the whole province. In the forty years since the founding of the People's Republic of China (to 1990), there have been seven droughts and three floods in the whole province, including two droughts in 1950s, floods 1 time, three droughts in 1960s, floods 1 time, droughts 1 time in 1970s and droughts/kloc-time in 1980s. The frequency of drought and flood in Huaihe and Huaibei areas is greater than that in other areas, and the frequency of drought in Yangtze and Jiangnan areas is less than that of flood disasters. Drought and flood disasters were the most frequent in the 1960s, and there was an increasing trend in the 1980s, especially in the 1980s.

Three. Variation characteristics of sunshine and solar radiation

Sunshine hours are the main indicators to measure the lighting conditions. The annual sunshine hours in Anhui province are between 1800 ~ 2500 hours. Among them, it can reach 2300 ~ 2500 hours/year in the north, and it is less than 2000 hours/year in Dabie mountain area and southern Anhui mountain area. The maximum fluctuation of sunshine hours in several years can reach more than 20%. Before the 1970s, there was plenty of sunshine in the whole province, and the annual sunshine hours were positive, 400-600 hours more than the annual average. After 197 1 year, the sunshine continued to be less.1971-kloc-0/980 averaged nearly 500 hours.1981-kloc-0/990 averaged 300 hours.

The measured data of solar radiation in Anhui Province are only available at Hefei Station. The analysis of Hefei station data shows that the total solar radiation is 1 15.4 kcal /cm2, of which 1953- 1960, 19 1- 1970. Since the 1970s, solar radiation has become less and less, especially since the 1980s. The annual total radiation of 198 1- 1990 is only 97.8 kcal/cm2, which is less than 17.6 kcal/cm2 on average. The reduction of solar radiation has a great impact on agricultural production, leading to a significant decline in agricultural climate production potential.

Four. Changes of agricultural climate production potential

There are many methods to estimate agricultural climate production potential. KassamWageningen method is adopted here, which comprehensively considers the influence of climate on crops and the dynamic process of growth and yield formation of different crops. According to the fact that the effectiveness of precipitation varies greatly in different parts of Anhui Province, the influence of precipitation on crop productivity is emphatically considered:

Y = y 1 (1-Vi)100% in the formula, y: climatic production potential, y1:light and temperature production potential, and vi: yield reduction rate caused by precipitation during crop I growth period:

Vi = Kyi (1-pi/etmi) (pi < etmi) vi = Kmi (pi/etmi-1) (pi > etmi), where kyi and kmi are the yield response coefficients of crops with water shortage and excessive water respectively. ETMi: crop water demand, Pi: actual water supply pi = ri-Siri: precipitation, si: surface runoff.

Using the above formula, the annual climate potential of the whole province in recent 40 years is calculated. The results show that the potential of climate production in the whole province was high in the 1960s and 1970s, but obviously low in the 1980s. The main reason is that the photosynthetic productivity is too low, which is 294 kg/mu lower than the average over the years and 47 1 kg/mu lower than that in the 1960s. The multi-year average ratio of climatic productivity to photosynthetic productivity is 0.54, 0.5 1 in 1960s and 0.59 in 1980s, which is the highest ratio in ten years. It shows that the heat condition, rainwater coordination and seasonal distribution are relatively reasonable in the 1980s, but the decrease of solar radiation makes the photosynthetic productivity decrease too much, which leads to the low climate productivity. Therefore, the lack of sunshine and solar radiation has great constraints on the agricultural development in the 1980 s and beyond.

Five, the impact of changes in agricultural climate resources on agriculture

Since 1980s, Anhui Province has shown a trend of warm winter and cool summer, with more precipitation and insufficient sunshine, which has a great influence on crop growth and agricultural layout. High temperature in winter is conducive to the safe overwintering and overwintering growth of summer crops, while cooling in spring is not conducive to the growth of overwintering crops in spring, and reducing precipitation in spring is conducive to reducing waterlogging damage. Therefore, the climatic conditions for the growth of summer crops have generally changed to a benign direction. In summer, due to the decrease of high temperature days and accumulated temperature, it is not conducive to the cultivation of double-cropping rice, which leads to the decrease of the area of double-cropping rice along the Yangtze River and in the southern region between Jianghuai and Jianghuai, but it is beneficial to the growth of single-cropping rice. Insufficient light leads to a significant reduction in climate production potential, which is not conducive to improving the yield per unit cultivated land area.

According to the changing characteristics of agricultural climate resources, our province should change the production mode and crop planting system in the future to adapt to the changes of agricultural climate resources. First of all, we should make full use of the characteristics of warm winter and cool summer to develop summer sowing crops, develop rape and hybrid rape to the north, and expand the planting area of wintering crops such as winter wheat. Secondly, appropriately reduce the planting of double-cropping rice and increase the area of one-season rice with high and stable yield. Thirdly, intercropping and interplanting should be adopted to improve multiple cropping index and photosynthetic utilization rate to make up for the lack of solar radiation. Fourth, vigorously build water conservancy facilities to prevent drought and flood disasters, especially to be alert to the harm of flood disasters to agricultural production. Fifth, cultivate new varieties of crops, further popularize new agricultural cultivation techniques, and strive to increase the yield per unit area.