| Precipitation is the most basic link in the process of the earth's hydrologic cycle.The inhomogeneity of rainfall distribution on the space and directly of time change affects the local water resources condition.Upstream of the Yellow River as the water source of the Yellow River,the precipitation has important effect on the basic conditions of water resources enough or not in the middle and lower reaches of agricultural and economic development needs.The research could reflects the trend of increase and decrease of vegetation coverage and the change of vegetation coverage on the precipitation effect of response time through the regional vegetation index changes and its response to precipitation factor,also has important significance to improve governance of basic grasp and adjust measures to local conditions to regional ecological environment.The previous studies about precipitation change of time and space usually using the data from weather stations.However,it is difficult to accurately show precipitation characteristics on the space and time due to the inadequate number of sites and their spatial distribution is not reasonable,thus affecting the relationship between vegetation and precipitation response study.In this paper the study area is the upstream of the Yellow River which includes Tianjun County in Qinghai province,Gangcha County,Gong he County,and Alashan league in Inner Mongolia,Minqin County,Wuwei City in Gansu province.From 1998 to 2014 as the research time,using time-space continuum precipitation data TRMM 3B43 obtained by remote sensing to analysis the spatial and temporal characteristics of precipitation,in order to obtain more accurate results.On the basis of this,using the NDVI data in recent 17 years in the study area to explore the vegetation on the response time of the precipitation effect.The results as followed:(1)TRMM 3B43 precipitation data can well reflect the rainfall distribution in the study area.The correlation coefficient between TRMM 3B43 annual precipitation data and the site observation annual precipitation data is 0.943,RRMSE=19.21%,TRMM 3B43 could meet the needs of years scale application.The correlation coefficient between four seasons precipitation data greater than 0.83,spring and summer is greater than 0.9.The RRMSE value of the spring,summer,autumn,respectively 29.49%?23.07%?31.32%,TRMM 3B43 able to accurately reflect the characteristics of the seasonal precipitation in the study area.The correlation coefficient between TRMM 3B43 precipitation data and site data is 0.932 on moon scale,RRMSE=47.55%,TRMM 3B43 month precipitation data through the study period is reliable in the study area.(2)The study area precipitation shoe obvious differentiation characteristics of space and time.The precipitation overall declines from south to north,from southwest to northeast to reduce.At the same time,there are complex spatial pattern of such as rainfall high value area in the south and higher area,relative high rainfall area south of Qilian Mountain and Bayan Har Mountains.Away from the influence of moisture arid areas include Alxa League and Utla banner.A maximum slope is 3.647,minimum value is0.443,and the average is 0.289.There are regions' trend of precipitation is slightly less such as Wuwei City,east of the Hexi Corridor,Qinghai lake basin,the middle of Qilian Mountain,Dragon Mountain,Heli Mountain,and the Badain Jaran Desert.Within the scope of the study area in other parts of the slope value greater than 0,precipitation is increased.The study area annual precipitation relative change rate between6% and 52.7% in the research on time series.Increasing overall performance from southwest to northeast,especially the temperate continental climate zone performance is outstanding.(3)The vegetation NDVI of the study area in 1998-2014 shows spatial and temporal variation characteristics significantly.The characteristics present the southern high spatial distribution of vegetation in the study area,the north-central low.In the season and scales are increased,the interannual timevariation characteristic shows autumn>summer>winter>spring.Evergreen coniferous forest,deciduous broad-leaved forest,mixed forests,closed shrub,sparse shrubbery,grassland,farmland,agriculture and natural vegetation mosaics,are on the rise in nearly 17 years,but the rate differences.(4)The maximum correlation coefficient between vegetation NDVI and precipitation in the study area mainly appeared in the first month.The 0.34% area of NDVI and monthly precipitation of maximum correlation coefficient in 3 months,another 3.9% area contains Inner Mongolia plateau of the largest correlation coefficient in 2 months,66.97% area contains the Aemye Ma-chhen Range?Qilian mountain?Inner Mongolia plateau?Liupan Mountain?Helan mountain of the largest correlation coefficients appear in the first month,28.75% area contains The eastern Qinghai-Tibet Plateau and southern Qilian Mountain appear in the corresponding month.(5)The vegetation types in the study area showed different response to different season precipitation characteristics.Evergreen coniferous forest,deciduous broad-leaved forest and agriculture and natural vegetation mosaics' maximum response of precipitation in the corresponding month in the spring,mixed forests,closed shrub,sparse bushes,grass and crops maximum response lag of precipitation for a month.Evergreen coniferous forest,mixed forest and agriculture with natural vegetation mosaics on the three stages of summer had no significant correlation with precipitation.Deciduous broad-leaved forest,closed shrub,sparse bushes,grass,crops showing the correlation between NDVI and summer precipitation is obvious.And the maximum response in the corresponding month.8 vegetation types showed significant correlation to three periods autumn month precipitation in the study area.The evergreen coniferous forest,mixed forest,closed shrub,sparse bushes,grass,crop,agriculture and natural vegetation mosaics maximum response appeared in the corresponding month,deciduous broad-leaved forest maximum response lag for a month. |
PDF Full Text Request