关键词: 黄土高原, 植被覆盖, 气候变化, 响应, 相关

Abstract:

EOF (Empirical Orthogonal Functions), SVD (Singular Value Decomposition) and lag cross-correlation were applied to analyze temporal and spatial response characteristics of vegetation cover to the variation of hydro-thermal condition, and distinguish the spatial-temporal correlation between vegetation index and climate factors. The results indicated that the hydro-thermal conditions have more principal components and worse regularity as well as minor variance contributes. The variation of hydro-thermal condition depends on monsoon climate, latitude, underlaying surface and so on, which is very complicated and changeable. But there are obvious characters in vegetation cover. The maximum based on lag cross-correlation method shows that the speed of wheat response of southern Loess Plateau to hydro-thermal condition is faster than forest, warm vegetation, cold-halophytic-drought plants and strong drought plants, and the lag-time is about 0-30 days, so more precipitation have stronger impact on vegetation growth than temperature. However, the minimum coefficient reflects that there is significant negative correlation between vegetation cover and double-cropping winter wheat and minor cereals in South Loess Plateau. Singular value decomposition illustrates that vegetation cover is in accordance with hydro-thermal condition in the same area, but there is still obvious negative correlation. Negative correlation is caused by crop-cutting and soil corrosion due to crop rotation system and climate type. It is the best condition for vegetation cover in southeast region of Loess Plateau. More precipitation will be the advantage for vegetation cover, including the hydrological effect of the Yellow River, but when the temperature is higher than one threshold value it won’t be an advantage for vegetation cover in arid and semi-arid region. Higher temperature makes plants grow well where there is sufficient moisture in arid region. The vegetation cover has close relations to hydro-thermal condition in valley plain and basin valley. When there is this additional condition, the vegetation cover increases in hydro-thermal equilibrium region. There is a high level of correlation between vegetation cover and hydro-thermal condition, but more limiting factors. The main limiting factors of temperature on the vegetation cover include land use, vegetation type, cropping system and landform. Loess Plateau is located in droughty inland region, so precipitation directly influences vegetation cover. Plant growth depends importantly on precipitation in desert zone and non-farming areas. In crop field, the correlation between vegetation and precipitation is further complicated by irrigation conditions and so on.

Key words: Loess Plateau, vegetation cover, climate change, response, correlation