Zhuqing ZHANG,Weixing GUO,Mengshuang PENG,Zhiyu WANG

Changsha Municipal Meterological Bureau,Changsha 410205,China

Responsible editor:Nana FAN Responsible proofreader:Xiaoyan WU

Changsha,the essential rice production area in China,locates in the central Hunan.Although Changsha is in the subtropical monsoon humid climate area,it carries distinct monsoonal and continental climate feature as Changsha is more than 700 km away from the ocean.Natural disasters happen now and then,such as high temperature damage,drought,cold-drew wind,low temperature in May,late spring cold,dry and hot wind,gale,hail,flood,cloudy and drizzly day,which is detrimental to the growth of rice and often results in low yield or even a total failure of the harvest.The drastic changes in temperature,light and water often exert significant effects on crops.Along with the global warming,there are different degrees of variations in the climate condition for rice production.According to the meteorological data from National Basic Meteorological Station in Changsha in recent 43 years and statistics of occurrence time and intensity of main meteorological disasters for rice in Changsha in recent 13 years,a comparison was conducted to the meteorological situations between the first 30 years and the last 13 years.Results indicated that the main meteorological disasters in rice production in Changsha showed an increasing occurrence tendency of high temperature damage,drought and cold-dew wind,but a decreasing occurrence tendency of low temperature,late spring cold,dry and hot wind,gale,hail,flood,cloudy and drizzly day.In the end,some corresponding strategies for preventing and reducing meteorological disasters in rice production were put forward.

Statistics Standard and Hazards of Main Climate Disasters

Standards and hazards of main climate disasters in rice production are shown in Table1.

Analysis of Major Climate Disasters

Late spring cold

In the last 13 years,the last ten days of April in 2001,2002 as well as2013,and the middle ten days of March in 2005 witnessed mild degrees of late spring cold,while the middle ten days of April in 2010 saw a heavy late spring cold.However,in the first thirty years,mild and moderate late spring cold occurred in the middle ten days of March in 1976,1978,1979,1994,the last ten days of March in 1996,1998,1999,the first ten days of April in 1979,1981,the middle ten days of April in 1983,and the last ten days of April in 1978,1982,1989.Intensive late spring cold took place in the last ten days of April in 1980,the last ten days of March in 1987,1988,1991,the middle ten days of April in 1991 and the middle ten days of March in 1996.

Table1 Statistics standard and damages of main meteorological disasters in rice production

Statistics suggested that the occurrence frequency of late spring cold in the last 13 years was 38%,which was 25% less than that in the first 30 years,while the occurrence frequency of intensive late spring cold in the last 13 years was 7%,which was 13%less than that in the first 30 years.Therefore,late spring cold weakened.

Low temperature in May

In the last 13 years,there was slight low temperature in May in 2003,and 2004,and intensive low temperature in 2002.In the early 30 years,there was mild low temperature in 1974,1976,1979,1981,1983,1984,1986,1992 and 1998,moderate low temperature in 1973,1987,1988 and 1993,intensive low temperature in 1975,1977 and 1991.

Statistics suggest the occurrence of low temperature in May in the last 13 years was 23%,which was 30%less than the frequency in the early 30 years.The occurrence frequency of low temperature in May was 0,but the frequency of intensive low temperature was 8%,which was the same as that in the early 30 years.Generally,low temperature in May occurred less frequently.

Cold dew wind

In the last 13 years,mild cold dew wind happened in 2002,moderate cold dew wind in 2008 and intensive cold dew wind in 2010,2011 and 2013.However,in the early 30 years,mild cold dew wind occurred in 1974,1972,1974,1977,1979,1980,1981,1982,1985,1988,1992,1994 and 1995,moderate cold dew wind in 1973 and 1984,and intensive cod dew spring in 1997.

Statistics suggested that the occurrence frequency of cold dew wind in the last 13 years was 38%,which was 15% less than that in the early 30 years(53%).The occurrence frequency of mild cold dew wind in the last 13 years was 8%,which was the same as that in the early 30 years,while the occurrence frequency of intensive cold dew wind increased by 20%.Generally speaking,cold dew wind is getting worse.

High temperature

Mild high temperature in the early 13 years took place in 2002,2004,2005,2006,2007 and 2008,moderate high temperature in 2001,2009,2010,2011 and 2012,and intensive high temperature in 2003 and 2013.However,in the early 30 years,there was mild high temperature in 1971,1972,1974,1975,1976,1977,1979,1984,1985,1986,1988,1990,1991,1994,1996,1998 and 2000,moderate high temperature in 1978,1980,1981,1982,1983,1989,1992 and 1995.

Statistics revealed that the occurrence frequency of high temperature in the last 13 years was 100%,which rose by 17% than that in the early 30 years.The occurrence frequency of moderate high temperature was 38%,which was 11%higher than that of the early 30 years (27%).The occurrence frequency of intensive high temperature was 15%,while that in the early 30 years was 0.Therefore,high temperature was getting worse.

Dry and hot wind

There was no dry and hot wind in the early 13 years,while in the early 30 years,such disaster occurred in the first ten days of July in 1977,1981,and the middle ten days of July in 1981,1990,and the last ten days of July in 1983 and 1991.The occurrence frequency was 20%,and most dry hot wind took place in the first and middle ten days of July,accounting for 67%.The frequency took up 33%,as such disaster tends to weaken significantly.

Flood

In the early 13years,there was mild flood in 2010 and 2013,the frequency of which was 15%,while in the early 30 years,mild flood occurred in 1971,1974,1982,1988,1995,1996 and 1999,moderate flood in 1980,1990 and 1997,and severe intensive flood in 1998.In comparison,the occurrence frequency of flood in the early 13 years was 21% less than that in the early 30 years,and the occurrence of mild and intensive flood was 0.Rainstorm occurs 3.7 times every year,generally 1.2 times in June,but such disaster tends to take place less frequently.

Drought

In the last 13 years,general scale of drought took place in spring 2005,winter 2008,summer and autumn in 2009 and winter in 2010.Severe drought happened in summer and autumn in 2003,autumn and winter in 2007.More severe drought happened in summer and autumn in 2013.In the early 30 years,general scale of drought happened in autumn and winter in 1971,winter in 1975,winter and autumn in 1976,winter in 1977,spring in 1978,autumn in 1979,autumn and winter 1981,autumn in 1982,autumn and winter in 1983,autumn and winter in 1985,autumn in 1986,summer in 1989,summer and autumn in 1990,autumn and winter in 1991,summer 1995,winter in 1998 and winter in 1999.Extremely severe drought happened in summer,autumn and winter in 1992.Drought happened every three years in Changsha,mostly in summer and autumn,sometimes in winter or spring,even continuous drought from summer to winter.For example,2003 witnessed severe drought in summer and autumn,2007 saw severe drought in autumn and winter,while 1992 and 2013 experienced extreme severe drought in summer,autumn and winter.

Statistics pointed out that in the last 13 years,the occurrence frequency of drought was 54%,which was 6%less than that in the early 30 years,and the occurrence frequency of drought and severe drought was 15%and 8% respectively,both of which was more than that in the early 30 years.As a result,drought is getting worse and worse.After the rainy season from July to September,the West Pacific Subtropical High Pressure hovered above Changsha,so the temperature there was extremely high,the evaporation was high and the precipitation was little.There was not any rain in 20 days in a row.

Gale

In the early 13 years,gale happened once in 2004,2005,2007,2010 and 2012,twice in 2002,three times in 2000 and 2006.In the early 30 years,gale happened once in 1972,1986 and 1995,twice in 1974,1977,1984,1997,and 1998,four times in 1975,1979 and 1996,five times in 1985 and 1988,seven times in 1976,1990 and 1994,eight times 1982,1991,nine times in 1983,eleven times in 1992,thirteen times in 1978,1980 and 1987.

Statistics indicated that gale happened once every year in the last 13 years,which was 3.8 times less than that in the early 30 years (4.8 times).Not a year in the last 13 years did the gale happen for four or more than four times,while in the early 30 years gale happened for four times in 2000,which means that the development of gale weakened.

Hail

In the last 13 years,hail happened once in 2001 and 2012,twice in 2009,and four times in 2010,while in the last 30 years,hail took place once in 1973,1976,1981,1982,1994,and 1995,twice in 1989,1993 and 1996,three times in 1984,1991 and 1992,four times in 1987 and 1988,five times in 1979.

Hail occurred 0.6 times in general each year in the last 13 years,which was 0.7 times less than that in the early 30 years.Hail happened for twice in 2009 and four times in 2010.The frequency of more than twice of hail in the early 30 years reached 30%.Therefore,the occurrence of hail weakened significantly.

Cloudy and drizzly day

In the last 13 years,the weather was cloudy and drizzling from April 19 to 25 in 2001,April 23 to 30 in 2002,March 2 to 8 and March 11 to 20,May 3 to 10 in 2003,May 23 to 29,July 14 to 30 in 2009,March 30 to April 8,May 12 to 19,September 22 to October 2 in 2010,March 18 to 24,May 31 to June 6 in 2011,March 2 to 9 in 2012,May 3 to 10 in 2013.In the early 30 years,the day was cloudy and drizzling on March 5 to 13,April 2 to 8,and April 13 to 19 in 1971,October 15 to 21 in 1972,March 1 to 14 and June 16 to 25 in 1973,March 5 to 15 in 1974,April 25 to May 3 in 1975,March 6 to 15,18 to 31 in 1976,April 4 to 10,May 5 to 16,June 14 to 22,September 24 to 29 in 1977,March 6 to 13 in 1979,March 1 to 8,11 to 17,20 to 26,April 19 to 26,August 10 to 17 in 1980,April 2 to 8,October 1 to 8,October 16 to 22 in 1981,September 9 to 20 and October 23 to 31 in 1982,April 10 to 22,October 19 to 25 in 1983,March 3 to April 8,October 3 to 9 in 1984,March 1 to 11,October 14 o 23 in 1985,April 25 to May 2,October 18 to 26 in 1986,March 8 to 16 in 1987,May 7 to 13,August 25 to September 6 in 1988,March 22 to April 1 in 1990,March 24 to 30 in 1991,March 12 to 27,June 19 to 26 in 1992,May 13 to 21,June 30 to July 8 in 1993,April 8 to 14,April 20 to 26,October 1 to 8 in 1994,April 13 to 18,October 18 to 24 in 1995,March 17 to 28 in 1996,March 15 to 22,June 18 to 24 in 1997,March 19 to 27,May 8 to 14,June 22 to 29 in 1998,March 23 to 29,August 10 to 16 in 1999,March 2 to 10,October 17 to 23 in 2000.

Statistics proved that the cloudy and drizzly day appeared 0.6 times in average in the last 13 years,which was 0.33 times less than that in the earlier 30 years (0.93 times).Besides,the cloudy and drizzly days often concentrate in March and April with a concentration of 64%.Therefore,the disaster weakened.

Measures to Prevent Major Climate Disasters

Late spring cold

Late spring cold affects the sowing and cultivating of seedlings.If such natural disaster happened in the middle ten days of March,it would delay the sowing period of early rice,while if such disaster took place after the sowing period,the early rice would be rotten and become withered,which would seriously impact the high yield of early rice and delay the timing.Ways to prevent late spring could in spring are as follow.First of all,the sowing and cultivating of early rice should be arranged properly to ease the danger of low temperature.The lowest temperature for the rice to sprout is 10 ℃,and the minimum temperature for the root of rice to grow is 15 ℃,so the sowing of early price should be around the time when the daily average temperature is 10 ℃and there is 80% guarantee rate,which is usually around March 23,or the time when the daily average temperature is 15 ℃and there is 80%guarantee rate,which is usually around April 20.Therefore,the appropriate sowing period of early rice in Changsha should be before or after spring equinox till early April,and the suitable cultivating period should be from the Grain Rain to April 20.Secondly,attention should be paid to weather changes by sowing in a sunny day in the late winter or the early spring.Thirdly,irrigation should be applied reasonably and fertilizing shall be scientific.Fourthly,disasters shall be prevented.Under the situation when the temperature is low and the weather is cloudy and drizzly,it is necessary to take precautions against large areas of rotten seedlings by washing out the white spots and injecting medicines.

Low temperature in May

It is detrimental to the tillering of early rice when there are more than five consecutive days of daily temperature lowering 18 to 20 ℃in the first ten days of May.The rainstorm can lead to large areas of dead seedling.The low temperature in the middle and last ten days of May has great influences on the earing differentiating of early rice.The earing differentiating is extremely sensitive to low temperature reaction,which is bad for the growth of pollen,and seriously affects the formation of flower organs.

Measures to prevent low temperature in May include the following aspects.Firstly,species are chosen wisely.Secondly,seedlings are transplanted in a sunny day.Thirdly,adequate fertilizer should be applied.Fourthly,irrigation should be conducted scientifically.

Cold dew wind

The low temperature and cloudy and drizzly days in the last growing period of late rice are harmful to the plants which are on the milk,and prolong the growth period,aggravate plant diseases and insect pests.Measures to prevent cold dew wind in autumn are listed as follow.First of all,it is necessary to plant safely by combining early and late rice species properly.Secondly,sowing is carried out on time to avoid the dangers of cold dew wind,around June 21 and June 15.Thirdly,field management should be strengthened and attention should be paid to the weather reports.Before the cold dew wind is coming,plenty water should be irrigated to adjust the temperature and fertilizing the leaves.

High temperature

The pollen of rice has become mature in the end of June and the rice began to sprout.This is a period when the rice is extremely sensitive to the climate.The most suitable day and night temperature should be from 28 to 32 ℃ and the temperature in the evening is 20 ℃.High temperature at this stage would result in the following situations.Firstly,the pollen will quickly lose its vitality after the flower breaking up.Secondly,the length of pollen is different,and short pollen cannot integrate with ovule.Thirdly,pollen is enlarging with the rising temperature as the end of pollen tube will break up when the temperature is above 35 ℃,and the pollen tube quickly becomes withered if the temperature is above 40 ℃.The most appropriate daily average temperature should be around 21 ℃,and the day temperature is 26 ℃while the night temperature was 16 ℃.In order to relieve the influence of high temperature on crops,it is necessary to choose plants which are heat resistant.Besides,transplanting should be carried out at an appropriate time to avoid the threat of high temperature which is most often from July 16 to August15.Thirdly,irrigation,watering,lowering temperature and spraying insecticides are carried out.Fourthly,afforestation can be made to improve the ecological environment.Fifthly,the water resources in the air can be made full use of by carrying out artificial precipitation to ameliorate the field climate.

Dry and hot wind

If the dry and hot wind blows when the early rice is in the milk,the crops would become mature in advance.There are four steps to prevent such result.Firstly,fertilizer can be applied on seedlings to enhance the fruiting rate.Secondly,irrigation can be applied more scientifically by irrigating during the day time and ejecting the water during the night.Thirdly,farmers can spray water once to lower the temperature by 2 ℃and increase the humid by 10% to 20%.Fourthly,chemical agents are sprayed to relieve the threats of high temperature.

Flood

In the main season for rice to grow,thunder shower can easily affect the photosynthesis and lead to flowers falling,plants lodging,and plant diseases and insects pests aggravating.Measures to prevent flood are as the following.Firstly,hydraulic works should be strengthened to dredge the river and to prevent the rivers from blocking.Secondly,agricultural ecological construction can be enhanced to plant trees and preserve water and soil,and to reduce the surface runoff.Thirdly,discharging of water can be made to ease the danger of flood.Fourthly,rainstorm monitoring and report can be made to provide service for the pre-warning of rainstorm,flood and mudslide.Fifthly,flood disaster relief can be made to prevent the spreading of various insects.Instant nitrogen,phosphorus and potassium should be applied immediately to promote the seedling growth.Besides,more seedlings should be planted if the damaged seedlings cannot be recovered.

Drought

Drought in spring affects the sowing of both early and late rice.Drought in summer exerts influences on the earing,sprouting and milking.Drought in autumn would delay the transplant and reduce the effective earing.In order to precent drought,hydraulic works should be built to conserve surface water first.Then,water resources in the air should be made full use of by carrying out artificial precipitation.At last,close attention should be paid to the weather report.

Gale

In recent years,gale weather has taken place less frequently,which is beneficial to the promotion of mechanical harvesting,but monitoring and reporting of gale should be strengthened to reduce its impacts.

Hail

Although hail happened much less frequently and its influences were limited,its destruction was intensive.For example,the evening of April 18,2013 saw hail in Ningxiang,Wangcheng and Kaifu.The loss in Ningxiang and Wangcheng was heavy,leading to 36 610 people dying,1380 people relocating,1015hm2crops being damaged,75 houses collapsed,5401 houses damaged,and 325 houses seriously ruined.The total direct economic loss amounted to 46.6 million.Precautions are as follows.Firstly,hail report can be made more precisely.Secondly,artificial hail mitigation can be carried out to promote hails change into precipitation.Thirdly,grass and trees are planted to improve the ecological environment and the condition to form hail cloud is damaged.Fourthly,agricultural disaster can be strengthened to reduce farmers’ loss.Fifthly,appropriate measures to remedy the damage should be applied in order to get a good harvest.

Cloudy and drizzly days

Cloudy and drizzly days affect the sowing and growth of early rice,and have little influences on the growth of rice in other periods.Therefore,following actions should be taken.Firstly,sowing and translating needs a good timing to avoid low temperature.Secondly,plastic film should be applied to control the small climate with the room and to prevent late spring cold.

Conclusions

The rice production is subjected to the weather and climate changes since rice grows in the field.Results indicated that the main meteorological disasters in rice production in Changsha showed an increasing occurrence tendency of high temperature damage,drought and cold-dew wind,but a decreasing occurrence tendency of low temperature,late spring cold,dry and hot wind,gale,hail,flood,cloudy and drizzly day.

It is imperative to monitor and report the climate disaster in advance,to enhance the service of modern agricultural production,to deal with the changes in climate disaster,to promote plastic film cultivating,to control the planting areas,to strengthen hydraulic works construction,to plant trees more reasonably,and to reinforcing final-stage management.Practices prove that the plantation of mid-maturing early rice and mid-maturing late rice together can effectively avoid the influences from cold dew wind in autumn so as to guarantee the high yield of early rice and late rice.

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