| As an agricultural weather hazard characterized by temperature,frost is one of the major agricultural weather disasters in China,with a great impact on grain production.The Huaihe River Basin is an important wheat producing area in China.It is of great significance to the disaster prevention and mitigation of the agricultural sector,to improve the economic income of the peasants and to ensure the national grain security by understand and master the spatio-temporal distribution and variation of the frost index.The daily minimum temperature of surface in the Huaihe River Basin from 1960 to 2015 comes from 61 meteorological stations were used in the paper.The temporal and spatial variation characteristics,mutation and period status of the first frost date,last frost date and frost-free date in the Huaihe River Basin were analyzed by the stepwise regression model,the Mann-Kendall mutation test,the sliding t test,the cumulative anomaly and the wavelet analysis.At the same time,the effects of geographical location,solar activity,circulation index and climate warming to the first frost date,last frost date and frost-free date were analyzed.The frost frequency and frost strength of different grades were analyzed.The risk zoning of late frost damage was made in ArcGIS9.3.The following conclusions are drawn from the study:(1)In the nearly 56 years,the average of the first frost date in the Huaihe River Basin was delayed by 2.22d/10a(p<0.001),and the last frost date has an ahead trend of 2.39d/10a(p<0.001),the average frost-free date was extended at a rate of 4.49d/10 a(p<0.001).On the spatial distribution,the first frost date was later in the south and earlier in the north,earlier in the mountains and later in the plains.The last frost date was earlier in the southwest later in the northeast,later in the mountains and earlier in the plains.The frost-free date was gradually reduced from southwest to northeast,longer in the plains and shorter in the mountains.(2)The mutations of the three frost indexes were analyzed by MK mutation test,cumulative anomaly and sliding t test.The results showed that the mutation of first frost date occurred in 1998,the last frost date was in 1995 and the frost-free date was in 1998.At the same time,the variation characteristics of the cycle are analyzed by wavelet analysis,the first frost date has an oscillation period of 2-6a;the last frost date and the frost-free date have an oscillation period of 2-4a.The latitude had a significant effect on the first frost date,the last frost date and the frost-free date in the Huaihe River Basin.With the increase of latitude,the first frost date was advanced at a rate of-0.44 d /0.1°(p<0.001),the last frost date was delayed at the rate of 0.49d/0.1°(p<0.001),and the frost-free date was shortened at a rate of-0.93d/0.1°(p<0.001).(3)In the latest 56 years,the stability of the first and late frost date in the Huaihe River Basin was weak in the southwest and strong in the northeast.The western mountains of Henan Province and Anhui Province mainly include poor stability in mountainous areas such as Funiu Mountain,Tongbai Mountain and Dabie Mountain.Frequency of abnormal first frost date was high in the south of the area and mountains,but the frequency of abnormal last frost date was lower than the first frost date on the whole,and there is a more significant reduction trend after 2000 s.In general,the stability in the west of Kaifeng-Gushi-Lu'an is poor,and we should pay attention to the adjustment of agricultural production layout in the future agricultural cultivation,the southern area and mountain areas should pay more attention to abnormal changes in early frost.(4)In the valley period of sunspots,the first frost date delayed,the last frost date advanced,and the frost-free date extended.The polar vortex area and strength index of the northern hemisphere,the polar vortex area and the intensity index of the Asian region have a significant negative effect on the first frost date,the last frost date and the frost-free date.The polar vortex index has a significant negative correlation with the first frost date,positive correlation with the last frost date,and frost-free date was significantly negative correlation,that is,the smaller the vortex area is,the weaker the strength,the first frost date delayed,the last frost date in advance,and the frost-free date extended.Northern hemisphere September polar vortex area index have a indicating meaning to the first frost date and the free-frost date,and February pole vortex area index have a greater significance to the last frost date.Climate have becoming warming in the Huaihe River Basin,and mutation occur in 1996,resulting in the first frost date gradually delayed,the last frost date gradually ahead of the year,and the frost-free date gradually extended,and especially in 2000 s performance is more significant.(5)The frequency and intensity of frost damage showed a decreasing trend in the Huaihe River Basin.The frequency and intensity of frost damage was higher in northeast and lower in southwest.The frost damage in the Huaihe River Basin is dominated by the light frost,and the high frequency range is wide.The proportion of moderate and severe frequency is similar,and the range of high frequency area is small.The process of the height of the range of intensity showed the south-west-northward changes.(7)The risk index of late frost damage in the Huaihe River Basin was slightly in the southwest and higher in the northeast,and the ratio of area of the high risk zone,higher risk zone,middle risk zone,lower risk zone and low risk area was 8.22%,15.31%,29.65%,34.66% and 12.16%,respectively.The defense of the frost damage in the north of Dingtao-Xuzhou-Suining-Funing line in the Huaihe River Basin is important. |
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