| Droughts are frequent extreme climate events that affect global changes in terrestrial ecosystems.Vegetation phenology changes are an important response mechanism of vegetation response to climate with asymmetric temporal effects.Exploring the temporal accumulation and time lag effect of drought on vegetation phenological period,which is the vegetation phenological and environmental cyclical change is an important content of resource environment research.In recent years,drought events have been frequent in Xilingol,and the growth of vegetation is affected by the drought environment,to investigate the correlation mechanism between meteorological drought and vegetation phenology.In this paper,we used the meteorological data and remote sensing data from 1982 to 2015 to analyze the temporal changes and spatial response characteristics of the dry and wet environment in Xilingol,to obtain the parameters of vegetation growth phenology,and to study the effects of multi-temporal scale drought on vegetation growth stages in Xilingol.The following conclusions were obtained.(1)The overall performance of the drought area in Xilingol: mild drought > moderate drought > severe drought > extreme drought,high frequency,and duration of drought in Xilingol from 1999 to 2015,increasing the impact range,with the area of mild and moderate drought accounting for a larger proportion,and the area of severe and extreme drought accounting for a lower proportion year by year.Winter and spring regional dryness and wetness alternate frequently,summer regional drought intensifies,and autumn drought occurs abruptly in 2010.The overall annual trend of drought showed a weak decreasing trend(-0.10d/10a),in which the increasing trend was mainly distributed in the northeastern meadow grassland,and the decreasing trend was mainly distributed in the southwestern desert grassland.The growing season SPEI tendency showed a decreasing trend from the desert grassland in the southwest to the sandy grassland.(2)The annual and growing season drought frequency is higher in the central part of the Xilingol region,the average frequency of spring drought is 28.58%,the drought duration is shorter,and the areas with greater intensity are mostly distributed in the northern part of the region;the average frequency of summer drought is 31.59%,the drought duration is longer,and the greater intensity values are concentrated in the southwestern part of the region;the average frequency of autumn drought is 31.91%,the drought duration is the longest,the greater intensity values are concentrated in the southeast of the region,and the drought intensity is more intense.(3)The start of vegetation growth in Xilingol is mainly concentrated in mid-late March to late April and is gradually delayed from southwest to northeast spatially.The end of vegetation growth period was mainly concentrated in 265-280 d,with an overall trend of advancement(-0.14d/a)and delayed from northeast to southwest.The spatial length of the vegetation growing season was gradually extended in the southwest,and the advancement trend was mainly distributed in the eastern and central parts of the study area.(4)The maximum correlation of short time scale drought on vegetation growth initiation period is mostly positive,and the vegetation growth initiation period is delayed with the accumulation of drought time in areas such as drought and low rainfall.The time lag analysis showed that the vegetation growth initiation period was influenced by the first 4 months of drought,and SPEI-9 and SPEI-12 with a 2-month lag had the highest response to the vegetation growth initiation period.(5)The end of the vegetation growth period in Xilingol is positively influenced by the monthly scale SPEI-1,and the short time scale wet and dry environment will delay the end of the vegetation growth period,and the proportion of negative correlation image elements between the end of the vegetation growth period SPEI-3,SPEI-6,SPEI-9 and SPEI-12 is higher,the vegetation enters the end of vegetation growth period earlier due to the long-term change of wet and dry environment.The time lag analysis showed that the lag effect of SPEI-1 in Xilingol mainly occurred in the first2 months of the season,and the lag effect of long time scale SPEI accumulation to June was particularly significant,and the significant correlation area reached the maximum on the scale of SPEI-3.(6)The maximum correlation between SPEI and vegetation growing season length at each time scale was negative at a regional scale,i.e.,drought prolonged vegetation growing season length in most of Xilingol.The time lag effect showed that the vegetation growing season length was most significantly affected by the time lag effect of SPEI-1 in the first 1and 3 months of the season.In the northern part of the study area,the time lag effect of vegetation growing season length was stronger,with a lag time of 4 months,and the vegetation growing season length in most of the region was affected by the time lag effect of drought in the first 3 months of the season. |
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