| Vegetation is an important ecological indicator and vegetation coverage level directly reflects the condition of the vegetation coverage in the region, while the vegetation coverage change reflects the change of ecological environment in a region. Beneficial results have been drawn through the study of the spatial temporal evolution of the vegetation coverage in the growing season in the West Liao River Basin from 2000 to 2010, which provided a reliable scientific basis and reference materials for the ecological management in the region. The main contents and conclusions of this study are as follows:(1) MOD13Q1 data of the growing season have been collected in the West Liao River Basin from 2000 to 2010 and the data have been pretreated. MOD13Q1 data have been reconstructed using Savizky-Golay filtration method, asymmetric Gaussian function fitting and double Logistic function fitting. The accuracy of double Logistic function fitting method is higher than that of the other two methods. Therefore MOD13Q1 data have been fitted using double Logistic function, which improves the accuracy of the data.(2) An inversed model of vegetation coverage in the growing season of the West Liao River Basin using pixel dichotomic model was constructed. The value of the key parameter NDVIsoil is the value of NDVI at the accumulation frequency of 0.5% and the value of NDVIveg is the value of NDVI at the accumulation frequency of 99.5% and the vegetation coverage is inversely calculated. Average monthly maximum coverage of the West Liao River Basin is 57.6% and the minimum is 25.6%. Medium and low coverage has decreased first to reach a peak before it rises again with a parabola shape, while the high coverage has the opposite trend. High coverage region has a wide distribution in July and August. It can be seen from the spatial distribution that the vegetation coverage in the West Liao River Basin in the growing season is in good condition and the overall vegetation coverage showed an increasing trend from west to east. High vegetation coverage areas are concentrated in the southwest, northwest and plains of the West Liao River Basin. Poor vegetation coverage is located in the east and northeast of Ongniud Banner throughout the West Liao River Basin.(3) Vegetation coverage in the growing season of the West Liao River Basin is mainly average or above coverage, and the coverage in 11 years accounted for 22.16%,24.79% and 32.99% in medium, medium high and high coverage, respectively, in the basin, while the medium low, low coverage and bare land accounted for 13.15%,5.95% and 0.95%. Four from the water district, the vegetation coverage in several regions of HeiMuLun River estuary, Chagan Mulun River, Xilamulun River, Yingjin River and the old Ha River prone to change, while it is relatively stable in the Jiaolai River, and in the area north of the LaoHa River it is substantially in the low coverage for a long period of time.(4) It has been found from the trend of the vegetation coverage in the West Liao River Basin that the area with significantly improved vegetation coverage in the growing season is 4080.25 km2, which is only 2.97%, severely degraded region is 3838.81 km2, which is only 2.80%, indicating that the area of improved and degraded vegetation coverage during the growing season is small, accounting for 5.77% of the West Liao River Basin area. Area with slight improvement is 44701.75km2, which is 32.58% of the total area, while the area of slight degradation is 69417.81 km, which is 50.59% of the total area, more than half of the basin area, indicating that there is a degrading trend of the vegetation coverage in the West Liao River Basin, mainly in the west and northwest, from 2000 to 2010 during the growing season.(5) According to Hurst exponential analysis of the vegetation coverage, the sustainability of the vegetation coverage in the basin has significant spatial differences, and in general the basin-wide coverage shows weak sustainability. Areas with strong anti-sustainability and strong sustainability are in scattered distribution.(6) From the Mann-Kendall nonparametric statistical test and Sen gradient analysis, vegetation of watershed area with improvement from 2000 to 2010 is smaller than the degraded vegetation areas. Areas with significant vegetation improvement are mainly in the Plain area of the West Liao River Basin. Areas with slight and severe deterioration are located west and northwest. It has been found from the coupling of Sen inclination with the Hurst exponential index that the vegetation coverage in 42.37% of the region in the West Liao River Basin in the growing season is in the right direction from 2000 to 2010, while there is a trend towards degradation in 57.64% of the region. Therefore, the vegetation coverage in the West Liao River Basin has a reducing trend.(7) It has been found from the method of correlation analysis that precipitation and vegetation coverage was positively related and the significant is relatively large. Precipitation played an important role for the vegetation coverage in the West Liao River Basin; average temperature and vegetation coverage had a negative correlation and the significance is relatively large. The average temperature had a counterproductive effect on the vegetation coverage in West Liao River Basin; reference evapotranspiration during the growing season and vegetation coverage in most regions showed a negative correlation, accounting for about 57%, while positive correlation is about 43%, mainly in the West Liao River Plain. Correlation coefficients were not significant in both cases. Regions with significant negative correlation are located in the northwest, east and southeast of the West Liao River Basin; regions with a significant positive correlation are mainly located in the West Liao River plain areas; underground depth and vegetation coverage were positively correlated in the West Liao River Basin, accounting for 50.29%, mainly located in west, north and south; and areas with negative correlation accounted for 49.71%, mainly in central, south and east. Average underground water depth is about 2-6 m for medium and high vegetation coverage. |
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