Comprehensive Risk Assessment Of Spring Frost Damage Of Tea Trees In Zhejiang Province

Tea plant(Camellia sinensis)is a warm leaf plant,which is mainly planted in subtropical and temperate regions of China.Zhejiang Province is the main tea planting area in China,and its tea export volume and export volume rank first in China.Tea is a cash crop with high economic value.From the beginning of early spring,tea buds germinate,and the earlier tea is picked,the higher its economic value is.Zhejiang Province is the main tea planting area in China,and its tea export volume and export volume rank first in the country.However,affected by the high-pressure cold current in the north in spring,the phenomenon of "late spring cold" often occurs in this area,which makes the tea buds suffer frost damage,resulting in the reduction of tea quality and even production,so that tea farmers have to bear the losses caused by frost.Frost will not only delay the growth of tea buds,affect the price and quality,but also cause the death of tea buds in serious cases,causing farmers to suffer greater losses.In recent years,the research on tea frost damage has gradually increased at home and abroad,but most of them are based on the internal and external indicators of the occurrence of frost damage of the plant to divide the threshold temperature for risk analysis,or the research on the temporal trend and spatial distribution of tea frost damage based on the threshold temperature of the occurrence of frost damage,while there are few studies based on the risk of tea spring frost damage,Moreover,risk analysis indicators are often single and solidified,and the data used are large-scale and rough data with low accuracy.Therefore,the research on the comprehensive risk assessment of spring frost damage of tea trees in Zhejiang Province is carried out.Based on the exploration of the frost damage mechanism of tea trees,the risk is assessed.The comprehensive system of Multi-source Satellite remote sensing data will be adopted to improve the practicability and refinement of the assessment results.Taking Zhejiang Province as the study area,tea trees were selected as the disaster bearing body of spring frost damage.Firstly,the meteorological,agricultural,remote sensing and economic data of Zhejiang Province are collected,and the risk assessment database of spring frost damage of tea trees in Zhejiang Province is established;Secondly,data processing,including normalization and assignment of positive and negative indicators,mainly the interpolation of cloud pollution missing value of MODIS LST data with resolution of 1km×1km and the construction of LST inversion fitting minimum temperature model;Then,according to the mechanism of spring frost damage of tea tree,the threshold of spring frost damage is determined,and the temporal and spatial distribution characteristics of spring frost damage are analyzed;Finally,combined with the "four factor" theory of regional natural disaster risk,this paper constructs a "comprehensive evaluation model of tea spring frost damage",comprehensively evaluates and divides the risk of tea spring frost damage in Zhejiang Province,and puts forward relevant countermeasures.The main results are as follows:(1)Based on the interpolation of MODIS LST data and the auxiliary variables(altitude,distance from water body,slope direction,etc.),the support vector machine is used to fit the minimum temperature,and the model for estimating the daily minimum temperature is established.The root mean square error(RMSE)and R-square of the model are 0.863 and 91.69% respectively.The average error between the fitted value and the actual value is less than 0.98℃.(2)From 1991 to 2020,the overall rising trend of the minimum temperature in spring(March and April)at Zhejiang meteorological station is not obvious,with strong volatility.There is an intersection in the MK test from 2019 to 2020.The analysis of the trend of minimum temperature change from 2003 to 2020 shows that although March is under the background of global temperature change of climate warming,low-temperature events still need to be vigilant and prevented.(3)The frequency and severity of spring frost damage to tea trees are strongly related to topography and climate,and is directly proportional to altitude.Affected by monsoon,it shows an increasing trend from southeast to northwest.Therefore,the intensity and frequency of spring frost damage are larger in the Middle East and north of Zhejiang,and smaller in the eastern coastal and central and western plain and valley areas.(4)The risk of spring frost damage of tea trees in Zhejiang has certain regionality and continuity.Most areas of the region are dominated by low and low risks.The adjacent areas of Lishui,Shaoxing,Taizhou and Jinhua are at high risk.The tea planting area and density in high-risk areas are large.Once spring frost damage occurs,it will often cause large economic losses.Therefore,the risk of spring frost damage of tea trees can be reduced from the aspects of adjusting the planting structure of tea trees,promoting excellent frost resistant varieties,increasing the construction investment of frost prevention facilities and equipment,improving the degree of mechanization of tea gardens and scientific management.The research results will provide theoretical basis and scientific and technological support for reducing the impact and loss of spring frost damage on tea trees in Zhejiang Province,monitoring and early warning of spring frost damage of tea trees,meteorological disaster prevention and reduction and agricultural production safety strategy.