Temporal And Spatial Changes Of Snow Depth In Mongolia Plateau And Its Impact On Grassland Vegetation Phenology

The fifth IPCC report shows that compared with the pre-industrial period,global warming has become a fact.Affected by this,the snow area in the northern hemisphere has a decreasing trend.The Mongolian Plateau is located in an arid and semi-arid area with little annual precipitation and uneven distribution.Snow and melt water are its important sources of water.Snow cover can avoid frostbite of vegetation and directly or indirectly affect the greening and yellowing periods of grassland vegetation.In this paper,the Mongolian plateau is used as a research area,and the 1982-2015 SMMR,SMM/I and SSMIS and GIMMS NDVI data are used to monitor the snow depth and grassland vegetation phenology of the Mongolian plateau.Impact on grassland vegetation phenology.The main conclusions are as follows:(1)The snow depth is very unevenly distributed in space,and gradually increases with increasing latitude.The low-snow area in the southwest is only 0.1mm,and the high-snow area in the north exceeds 86 mm.Affected by the increase in temperature and the decrease in precipitation(P<0.05),the snow depth decreased at a rate of 0.49mm/10 a,with a decrease area of 61.52%,an increase area of 38.48%,and a significant increase of 5.36% area.(2)The spatial distribution of vegetation NDVI is extremely uneven,and it gradually increases from southwest to northeast.The vegetation NDVI in Alxa area is less than 0.1,and the vegetation NDVI in the northern area of Greater Xing'an Mountains is 0.7.In recent years,vegetation NDVI has increased at a rate of 0.002/10 a,with an increase of 62.17%,an increase of 34.04%,and a decrease of 37.83%.Meadow NDVI,typical grassland NDVI,desert grassland NDVI,and alpine grassland NDVI all showed a slow increasing trend,among which desert grassland NDVI increased slowly at a rate of 0.000006/10 a.Vegetation rejuvenation is concentrated in mid-April to early May.In recent years,it has advanced at a rate of 0.45 days/10 a,with 56.05% in the advanced area,43.95% in the delayed area,and 11.53% in the significantly delayed area.In recent years,meadow grassland SOS,typical grassland SOS,desert grassland SOS,and alpine grassland SOS have all shown a slow advance trend.Among them,typical grassland SOS advances at the rate of 1.01 days/10 a,the rate of advance is the fastest.and meadow grassland SOS at 0.04 days/10 a,the rate of advance is the slowest.Vegetation yellowing is concentrated in mid-September to early-October.In recent years,it has advanced at a rate of 0.99 days/10 a,with 68.06% in the advanced area,31.94% in the delayed area,and 5.74% in the significantly delayed area.In recent years,meadow grassland EOS,typical grassland EOS,desert grassland EOS,and alpine grassland EOS have all shown a slow advance trend.Among them,desert grassland EOS has the fastest advance at a rate of 1.89 days/10 a,and meadow grassland EOS at 0.43 days/10 a,The slowest rate of advance.The length of the vegetation growing season is mainly concentrated in 110-170 days.In recent years,it has been shortened at a rate of 0.54 days/10 a,with a shortened area of 58.45%,an extended area of 41.55%,and a significantly extended 14.70%.In recent years,the meadow grassland LOS,typical grassland LOS,desert grassland LOS,and alpine grassland LOS have shown a trend of slowing down.Among them,the desert grassland LOS has the fastest reduction at a rate of 0.86 days / 10 a,and the meadow grassland LOS at 0.30 days/10 a,the rate of reduction is the slowest.(3)In the high snow depth area of the northern Mongolian plateau,the snow water melted after the reduction of snow cover is more likely to be absorbed by surface vegetation,resulting in early vegetation greening period.The significant positive correlation is 39.39%.Meadow grassland snow depth and greening period,typical grassland snow depth and greening period,desert grassland snow depth and greening period,alpine grassland snow depth and greening period are all positively correlated,of which meadow grassland snow depth and greening period,typical grassland snow depth It was positively correlated with 0.47(P<0.01)and 0.49(P<0.01)respectively during the greening period.Since the vegetation yellowing period is concentrated in September-October and snowfall mainly occurs after October,the snow depth has a weak influence on the vegetation yellowing period,and the snow depth has no significant effect on the vegetation growth period.