Monitoring Heat And Drought Stress Of Wheat In Main Wheat-Producing Areas Of China Based On Remote Sensing Data

The latest IPCC report points out that with the continuous rise of greenhouse gases,the goal of limiting global warming to 1.5℃ is become difficult to achieve.Meanwhile,the frequency and amplitude of extreme climatic events such as heat waves,droughts and extreme rainfall are increasing.Currently,the most important challenge for agriculture is that more and more people need to feed in the next few decades.Wheat is the third largest grain crop in China,accounting for about 20% of the total grain yield in China,while the frequent occurrence of extreme climatic events will bring negative impacts on the growth and yield of wheat.At present,remote sensing vegetation indices based on reflectance are the main method to monitor heat and drought stress on crops.However,vegetation indices only reflect the change information of vegetation canopy structure.At the early stage of drought and heat stress,vegetation indices are unable to reflect the response of stress on crops in time.Solar-induced Chlorophyll Fluorescence(SIF)is closely related to vegetation photosynthesis,which provides a new tool to monitor heat and drought stress on crops.However,the ability of satellite SIF data to monitor heat and drought stress on wheat in China has not been deeply studied.In this paper,we analyzed the temporal and spatial distribution characteristics of heat wave and drought in main wheat producing areas of China from 2007 to 2014;In addition,the most suitable drought indice was selected by comparing the monitoring performances of different drought indices on soil moisture and wheat drought stress;Moreover,taking the heat stress in North China Plain and the drought stress in Hubei,Anhui and Jiangsu provinces as typical cases,we compared the abilities of satellite SIF and vegetation indices to monitor heat stress and drought stress on wheat.The datasets employed in this study mainly include meteorological data,vegetation indices data,satellite SIF data,wheat yield data,and so on.The main work and achievements of this paper are summarized as follows:(1)The variation trends of heat wave and drought in main wheat producing areas of China in recent 10 years showed great spatial heterogeneity.The increasing trend of heat wave was mainly concentrated in the low and high latitudes of China,and the increasing trend of drought was mainly concentrated in the low latitudes of China,especially in the southwest of China.In addition,Pearson and Spearman correlations between PDSI drought index,SPEI drought index at different time scales and Vegetation Condition Index(VCI),Soil Moisture Condition Index(SMCI)were also calculated.The results showed that SMCI has significant positive correlations with PDSI and SPEI at 1,3,6 and 12-month scales in most areas of the study area.In particular,SMCI has the greatest correlation with SPEI at 1-month scale,which means that the SPEI at 1-month scale was most suitable for the temporal and spatial analysis of drought in main wheat producing areas of China.(2)As the most important wheat producing area in China,the average temperature,maximum temperature and minimum temperature in North China Plain have increased from 1983 to 2014,especially the minimum temperature;Consistent with the increasing trend of temperature,the number of heat wave days in wheat planting area of North China Plain also increased significantly,with an increase of 10 days every 10 years in the past 30 years;From the perspective of spatial distribution,the increasing trend of heat wave days in the southern part of North China Plain was significantly higher than that in the northern part,with the continuous increase of temperature and the decrease of precipitation in the southern part,wheat in the southern part may face more extreme climate risks in the future.Furthermore,we explored the response differences of GIMMS NDVI and GOME-2 SIF to monitor heat stress on wheat in North China Plain.The results indicated that the correlation between SIF and wheat yield was significantly higher than that of NDVI,and the SIF can also well capture the wheat yield reduction caused by heat stress in 2009;Moreover,compared with NDVI data,satellite SIF not only show a greater decline slope for the increase of heat wave days,but also respond earlier to heat stress.Therefore,satellite SIF data has stronger heat stress monitoring ability than NDVI.(3)In the winter wheat growing season in 2011,Hubei,Anhui and Jiangsu provinces experienced severe drought stress,and the response ability of SIF and vegetation indices to wheat drought stress were evaluated.The 1-month scale SPEI index indicated that the drought stress lasted from January 2011 to May 2011,and almost throughout the whole wheat growing season;The drought was characterized by moderate and severe degree;In terms of spatial distribution,the drought first occurred in the southern part of the study area,and then gradually extended to the northern part,until it spread to the entire study area.The analysis of drought stress response based on satellite remote sensing data showed that the GOME-2 SIF data can better capture the shortening of wheat growth period caused by drought,and in the early stage of drought,the response of SIF data to drought stress was better than MODIS NDVI and EVI data in timeliness,sensitivity and spatial distribution.However,vegetation indices were more feasible when wheat was subjected to drought stress for a long time.