| In this paper,two kinds of remote sensing data,GIMMS-NDVI 3gV1.0 and Landsat-NDVI,are used as data sources to combine various meteorological data(such as precipitation,temperature,sunshine duration,relative wetland,wind speed,etc.)to improve the utilization of light energy.The model-CASA model was used as a carrier to study and construct NFP long-term sequence data sets at different time scales(interannual,growing season,and year).In terms of time evolution,not only the trend line fitting,wavelet analysis and MK mutation detection are used to analyze the one-dimensional characteristics of the trend,periodicity and abrupt change of the NPP values??of the Zoige Wetland,and also by means of the centroid.The model studied the interannual and annual centroid changes of the NPP in the Zoige Wetland from the two-dimensional eigenvalues.In terms of spatial pattern,two-dimensional wavelet analysis method is used to reveal the multi-scale spatial pattern characteristics of NPP multi-year average,multi-year trend and annual variability of Zoige wetland.Further,the centroid model and the two-dimensional wavelet method are used to study the driving force of NPP evolution in the Zoige wetland from the regional and pixel scales,and multi-scale analysis is carried out.Research indicates:(1)In terms of time evolution,the interannual variation of vegetation NPP in the Zoige Wetland during the 34 years from 1982 to 2015 showed a downward trend.The interannual variation is dominated by the interdecadal cycle of the 15-year scale,and the global characteristics are significant;the interannual periodic changes of the scale less than 10 years are centered on the 4th and 7th scales,and the local characteristics are obvious.The trend of the decline in the annual average of NPP reached the level of mutation in 1986.The interannual centroid movement of NPP in the Zoige Wetland is characterized by a change in northeastward NPP from 1982,a southwestward atrophy change from 1985 to 1989,and an alternating change from northeastward to southwestward atrophy in 2000 and 2000.After the relative westward stable change,and the relatively eastward stable change after 2009.During the year,the NPP of the Zoige Wetland also showed a downward trend,which was the most prominent in October and the least significant in March.The cyclical changes also have the strongest change in the interdecadal cycle of the 17-year scale,which is prominent in 2,5,6,and 7 months;the interannual cycle of the 3-year scale is also strong,which is prominently reflected in 4,5,9,and10,November.Most of the(3,5,6,7,8,9,10,and November months)there was a sudden decrease in the NPP value,and the time was also started in 1986.The annual trajectory of NPP centroid movement in the Zoige Wetland is from January to December,roughly:Northeast>West to North>Southeast>West to North>Northeast>Southwest>Northeast.(2)In the spatial pattern,the dominant scales of NPP for the Zoige Wetland are46.39,139.64,692.42,1034.35,1309.1 km~2,46.39 and 692.42 km~2,and the change direction of NPP is mainly in the vertical direction,while 139.64 On the three scales of 1034.35 and 1309.1 km~2,the change is mainly in the horizontal direction.The dominant scale of the NPP trend in the Zoige Wetland is 9.28,32.9,and 139.63 km~2.On the two scales of 9.28km~2 and 139.63km~2,the horizontal direction changes mainly,while on the 32.9km~2scale,it changes mainly in the vertical direction.The dominant scales of NPP annual variability in the Zoige Wetland are 46.39,105.46,and 838.12km~2,which are mainly in the vertical direction on the 46.39 km~2 and 838.12 km~2scales,and mainly in the horizontal direction on the 105.46 km~2scale.(3)On the regional scale,the NPP evolution of the Zoige Wetland is mainly affected by the positive action of precipitation and the negative effect of temperature,and the total sunshine hours and effective monthly accumulated temperature are relatively low.On the pixel scale,the positive impact of precipitation on the NPP of the Zoige Wetland is more pronounced in the western region;the negative impact of total sunshine hours is more pronounced in the northern and southern parts of Zoige.(4)The direction and trend of the centroid change of the annual average value of NPP in the Zoige wetland maintains a high consistency with the direction and trend of the centroid change of the regional precipitation,reflecting the leading role of precipitation on the temporal and spatial variation of NPP in the Zoige Wetland.The multi-year average of NPP and the multi-year average trend scale of the Zoige Wetland show the dominant role of precipitation in the horizontal direction and temperature in the vertical direction,indicating that the precipitation direction scale is mainly in the horizontal direction,while the temperature main influence direction scale is the vertical direction. |
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