Study On Dry-hot Wind Disaster Monitoring In Middle South Of Hebei Province Based On MODIS Data

Dry-hot wind is also called“dry wind”,“hot dry wind”,etc.It is a kind of disaster caused by extreme weather and one of the most serious disasters in North China Plain.It is one of agricultural meteorological disasters,usually accompanied by high temperature,low humidity and certain wind power.Different from drought,dry-hot wind is caused by sudden increase in temperature in a short time,rapid drop in humidity and auxiliary role of wind,so that wheat lose water by transpiration,resulting in cell structure destruction,photosynthetic rate decrease,chlorophyll content change and root activity weakness,making wheat dry from top to bottom and even dead.Remote sensing technology has the characteristics of wide coverage,strong timeliness and wide applications.At present,there are few researches on remote sensing application in dry-hot wind meteorological disaster.Most of them are based on meteorological monitoring and cannot reflect the specific impact of dry-hot wind disaster on winter wheat crop and soil moisture conditions.The purpose of this study is to use remote sensing technology to monitor the growth of winter wheat under dry-hot wind disaster,and to compare the evaporation before and during dry-hot wind occurrence in combination with meteorological data.Finally,the effect of dry-hot wind disaster on soil moisture is evaluated,so as to provide assistance for agricultural meteorological disaster and agricultural production,to prevent and monitor the occurrence of dry-hot wind using scientific method,and to avoid adverse effects on food production.The main research contents of this paper are as follows:?1?Monitoring dry-hot wind using reflectance spectra and vegetation indices.Based on MODIS reflectance data,spectral reflectance change of winter wheat before and during dry-hot wind occurrence were compared,and a variety of vegetation indices were constructed and compared,to explore the impact of dry-hot wind on the growth of winter wheat.?2?Monitoring dry-hot wind using evapotranspiration.Based on SEBS model,the evapotranspiration of the study area was simulated,using MODIS solar zenith angle data,surface reflectance data and surface temperature data,combining with meteorological data.The spatial distribution of daily evapotranspiration before and during dry-hot wind occurrence was compared,and the relationship between temperature and evapotranspiration was analyzed.?3?Using MODIS surface temperature data,surface temperature changes before and during dry-hot wind in the study area were compared,and TVDI was constructed in combination with EVI to study the spatial distribution of TVDI and surface moisture conditions before and during dry-hot wind occurrence.The relationships between temperature,evapotranspiration and TVDI were analyzed,and the degree of drought during dry-hot wind was assessed.The main conclusions of this paper are:?1?Using MODIS surface reflectance images,the spectral reflectance of winter wheat before dry-hot wind occurrence?May 21,2014?and during dry-hot wind?May 28,2014?were extracted.The spectral reflectance values during dry-hot wind decreased compared with those before the occurrence,and reflectance at center wavelengths of 0.86?m and 1.24?m were significantly lower than those before dry-hot wind occurrence.?2?A variety of vegetation indices were constructed using band values??of surface reflectance products,and vegetation indices values before and during dry-hot wind occurrence in the study area were compared.NDVI,EVI,ARVI and RVI values decreased significantly during dry-hot wind occurrence,while PSRI and SIPI showed an increasing trend.By comparing the numbers of pixel with different vegetation indices,the peak values of NDVI,EVI and ARVI moved to low values during dry-hot wind occurrence.The peak value of RVI did not change significantly,while peak values of PSRI and SIPI moved to high values.The maximum value of EVI dropped from 0.73 to 0.55,with the most obvious change.Therefore,EVI was the best to monitor dry-hot wind disaster.?3?By comparing evapotranspiration simulated by SEBS model before and during dry-hot wind occurrence in the south-central part of Hebei province,it was found that the daily evapotranspiration of winter wheat planting area in the central Hebei province before dry-hot wind occurrence was around 5-6 mm·d^-1.The daily evapotranspiration in the southern winter wheat planting area was relatively low,about 0-4 mm·d^-1.The daily evapotranspiration increased significantly as a whole when dry-hot wind occured,and the pixel value at 6-10 mm·d^-11 reaches 74.67%.By comparing the actual evapotranspiration with the simulated evapotranspiration at stations,the difference between SEBS simulated value and actual value was small.Therefore,SEBS model could be used to effectively estimate daily evapotranspiration during dry-hot wind occurrence.?4?TVDI was constructed by using NDVI and EVI and MODIS surface temperature products to analyze the characteristics of wet edge and dry edge.It was found that the fitting effect and change trend of dry edge and wet edge of EVI were more obvious,and EVI could be used to build TVDI under dry-hot wind disaster.TVDI values were higher overall during dry-hot wind occurrence than those before dry-hot wind occurrance.By comparing the numbers of TVDI pixels before and during dry-hot wind occurrence,it was found that TVDI peak value shifted to high value during dry-hot wind occurrence,from 0.3 to0.67.?5?Linear regression analysis between evapotranspiration and TVDI values??before and during dry-hot wind occurrence showed that evapotranspiration had a decrease trend with the increase of TVDI,and TVDI value and evapotranspiration of points during dry-hot wind occurrence were higher than those before dry-hot wind occurrence,indicating that dry-hot wind could cause drought disaster.By constructing three-dimensional plots of evapotranspiration,TVDI and temperature,it was clear that surface temperature was proportional to evapotranspiration and TVDI,and evapotranspiration increased with the increase of surface temperature.