1 Impact of agricultural meteorological disasters on agricultural production
Figure 1 shows the environmental monitoring data obtained by using a multi-parameter environmental monitoring instrument. It can be seen from Fig. 1 that since 1971, Liaoning Province has experienced the occurrence of agricultural meteorological disasters each year, and has become parallel to various degrees of disasters. 
The area affected by crops and disasters showed periodic fluctuations, and the degree of damage of agricultural meteorological disasters was negatively correlated with the total grain output in the corresponding years. With the improvement of the level of agricultural science and technology, grain production has generally increased, which is 210.2@104t/10a. The total food production in 1971 was 881. 5@104,t in 2008 it was 1 860.3@104, and t was 2.1 times in 1971. In 1989, 1997, and 2000, the agro-meteorological disasters were relatively serious. The comprehensive disaster disasters were severely affected. The disaster area in the province was 177.1@104~189. 0@104hm2. The total grain output in each year was reduced by 346.6@104~508 from the previous year. 8@104t. From 1990 to 1999, the total grain output was above 1 313.5 @ 104t. The total area affected by agro-meteorological disasters in 2000 was 283.0@104hm2, resulting in a total grain output of only 1 140@104, and t was the lowest value from 1990 to 2008. From 2001 to 2008, with the reduction of meteorological disasters, the total grain output showed a steady increase. It can be seen that if the crops are affected by severe weather or adverse weather conditions during the vegetative growth stage, but after the late conditions have improved, the crops have the characteristics of restoring or making up for these effects, and the impact on the final yield is small; but in the crop reproduction During the growth stage, especially in the early stages of reproductive growth, if adverse or adverse weather conditions are encountered, even if the late conditions are improved, the crop growth will be difficult to recover or make up, and eventually will have a greater impact on the yield, or even no harvest.
2 Timing Changes of Agricultural Meteorological Disasters To further understand the occurrence characteristics of annual meteorological disasters, the agricultural sector used agricultural environmental detectors to analyze the statistical data of four categories of agricultural meteorological disasters in Liaoning Province from 1971 to 2008. The results showed that in 38 years, the frequency of drought and flooding was the highest, which was 95%. The frequency of low-temperature freezing damage was the lowest, which was 47%. The disaster-affected area of ​​drought disaster accounted for 63.0% of the total disaster area in the year, followed by flood disaster 22.3%, wind and natural disaster 9.8%, and low temperature and frost damage accounted for 3.9%. . Since 1988, the proportion of drought disasters has basically been above 50%. In particular, drought disasters in 1972, 1982, 1988, 1999, 2000, 2003, 2004 and 2007 accounted for over 91% of the total. The proportion of drought disasters increased at a rate of 5.8%/10a, while the proportion of other disasters showed a decreasing trend. Floods decreased at a faster rate of 2.8%/10a, and windbreaks and low-temperature damages accounted for 1.6% and 10a respectively. The rate of 1.1%/10a decreases (Figure 2). It can be seen that the drought disaster has become the main factor affecting agricultural production in Liaoning Province.
3 Assessment of major agrometeorological disasters and comprehensive disaster assessment As can be seen from Table 1, during the 38 years, the low-temperature freezing damage in the four types of agrometeorological disasters was based on minor disasters. 
The Lord has appeared for 29 years, accounting for 76%. Other disasters are mainly light disasters, accounting for 45% to 68%. The years of severe and severe disasters caused by flood, wind, and cold disasters are 3 to 7 years, and the severe and severe disasters caused by drought are 8 years. It can be seen that the drought brought the most serious losses to Liaoning Province. During the 38 years, the disaster index of agricultural meteorological disasters in Liaoning Province showed a phase change, with an increase of 0.61 every ten years, that is, the degree of damage from agricultural meteorological disasters to agricultural production gradually increased with time (Figure 3). During the period from 1971 to 1993 when the disaster was mild, 83% of the disasters occurred in minor disasters and the following disasters. In the period of heavy disaster from 1994 to 2003, 80% of the disasters occurred in the middle and above years; the period of lighter disasters occurred from 2004 to 2008. , Occurrence of minor disasters and the following disasters accounted for 80% of the year. Comprehensive assessment of agricultural meteorology 
Disasters are the largest year for minor disasters, accounting for 15 years, accounting for 39% of the total years; light disasters for 10 years, accounting for 26%; catastrophes and disasters are the least, both appear for 3 years, accounting for 8%, and the disasters appear 7 year. In 1989, the disaster was the worst, with a disaster index of 7.13; the lightest in 1976, with a disaster index of only 0.17.
4 Drought disasters change law Since the frequency and severity of droughts in Liaoning Province exceed those of other meteorological disasters, the analysis of drought disasters is focused on. Some studies have found that droughts in Liaoning Province are dominated by spring drought, accounting for more than 70% of the total number of droughts. The occurrence of spring droughts is obviously regional, and there is no obvious pattern in areas where summer drought and autumn drought occur. As can be seen from Fig. 4, drought disasters show a certain degree of regular fluctuations, and the disaster area increases at a rate of 1.08@104hm2/10a. In the 38 years, the average drought-damaged area in Liaoning Province was 106.91@104hm2, the area affected by the disaster was 53.59@104hm2, and the area lost was 9.27@104hm2. Crops were produced in 1972, 1989, 1997, 1999, 2000, 2001, 2003 and 2007. The area of ​​the disaster was 94.10@104~151.13@104hm2, both of which were severely catastrophic or extraordinary disasters. In 1985, 1986, and 1998, the affected area was less than 28.00@104hm2, and the affected area was <16.67@104hm2, which had little impact on agricultural production. 
From the monitoring data of the small-scale automatic weather station in Figure 5, it can be seen that the variability of the disaster rate of drought has changed gradually, with an increase of 0.31 every 10 years, that is, the degree of drought caused by drought has increased. From 1971 to 1996, it was a light disaster period. The year of minor disasters accounted for 77%; during the period 1977-2008, it was a major disaster, and the major disasters and above years accounted for 67%. In 2000, the variability of the rate of natural disasters was the largest and the degree of damage was the greatest. Comprehensive assessment of disasters reached the level of severe disasters. The main reason was that the drought reached the level of severe disasters, resulting in a significant reduction in grain production in the province.
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