| Drought is one of the most serious natural disasters in the world,which has the characteristics of high frequency,wide range,long duration and strong harmfulness.As the largest winter wheat growing area in China,the Huang-Huai-Hai Plain is frequently affected by drought during its main growing period,which has serious impact on agricultural production,food security and economic development.The drought index is now numerous,but different drought indexes have different quantification methods,different applicability and different requirements for basic data.Therefore,selecting suitable drought index to monitor the drought in Huang-Huai-Hai Plain and pointing out the basic law of drought development is of great significance to increase the winter wheat yield in the study area.This study with winter wheat of Huang-Huai-Hai Plain as the research area,based on standardized precipitation evapotranspiration index(SPEI)of drought evolution characteristics analysis and identification of typical drought years,the spatiotemporal sensitivity and applicability of remote sensing drought index were analyzed in the main growing periods of winter wheat in typical arid years.The main results are as follows:(1)From 1981 to 2015,SPEI on all time scales indicated that the Huang-Huai-Hai Plain showed a weak trend of drought,with frequent spring and winter droughts.During the 35 years,more than 30% of meteorological stations in 23 years experienced mild drought.The drought was the most serious with high frequency and severity from 1997 to 2002.In March,April and May,the meteorological stations in the study area had an increasing trend of drought,the growth rate of the meteorological stations suffering from drought was 9.8/10 a,0.07/10 a and 1.5/10 a,respectively.The drought level showed an aggravating trend,and the change trend in March was up to 0.24/10 a.Taking all time scales SPEI into consideration,in recent ten years,the drought in 2014 was relatively serious during the main growth period(from March to May)of winter wheat.(2)Taking the main growth period of winter wheat in 2014 as an example,the correlation analysis of each remote sensing drought index and the site-based SPEI indicated that both the temperature vegetation drought index(TVDI)and the temperature state index(TCI)were able to monitor the drought during the main growth periods of winter wheat in Huang-Huai-Hai Plain.Moreover,in March and April,the TVDI had the highest correlation with SPEI,with the correlation coefficient r of-0.533 and-0.349 respectively,and the fitting degree r~2 of 0.28 and 0.12 respectively.In May,TCI had the highest correlation with SPEI,r=0.496,r~2=0.24.The vegetation status index(VCI)had a low correlation with SPEI and even presented a negative correlation in March,r=-0.035,r~2=0.001.In terms of space,TVDI was more sensitive to drought monitoring,which was basically consistent with SPEI’s drought monitoring results;TCI failed to detect or overestimate drought events in some areas;VCI was less sensitive to drought events,especially in the southern part of the study area.(3)Taking the main growing period of winter wheat in 2014 as an example,the correlation analysis of each remote sensing drought index and soil moisture(SM)retrieved by remote sensing showed that in the main growth period of winter wheat in Huang-Huai-Hai Plain from March to May,the correlation between the three drought monitoring indexes and SM was TVDI>TCI>VCI,and the absolute value of TVDI’s correlation coefficients in March to May all exceeded 0.544,showing an extremely significant negative correlation.In terms of space,TVDI failed to monitor the local drought in the central and eastern part of the study area in April,and the test results were basically consistent with those of SM in other areas.TCI failed to monitor the drought events in the central and eastern part of the study area in March and April,and overestimated the drought events in the northern edge of the study area in May.VCI monitoring results showed that most areas were excessively wet,and TVDI was generally more applicable than TCI and VCI in the study area.(4)From 2001 to 2017,there was little difference in interannual variation of the drought area in the main growing period of winter wheat.The drought occurred with wide range and high frequency,the drought area above mild fluctuated between 70% and 85%,and the drought area above moderate fluctuated between 20% and 40%.From 2001 to 2017,the average drought grade distribution map of winter wheat in Huang-Huai-Hai Plain during the main growing period showed that the drought was the most serious in March,the overall drought situation slowed down in April but the regional difference was large,the moderate drought area decreased but the mild drought area increased in May,and almost the whole study area showed drought.There was a marginal effect in the main growth period of drought and the trend was significant,the southeastern part of the study area was arid and the central part was humid.The conclusion of this study is that the temperature vegetation drought index(TVDI)has the strongest suitability in the main growth period of the winter wheat area of the Huang-huai-hai Plain,followed by the temperature state index(TCI),and the vegetation state index(VCI)has the weakest adaptability.The frequency of drought in the winter wheat area of the Huang-huai-hai Plain was high and the range was wide,and the drought level was dominated by mild drought There was a marginal effect in the main growth period of drought and the trend was significant. |
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