关键词: 干旱, 地形分异, 海拔高度, 坡度, 坡向, AVI

Abstract: On the base of EOS MODIS data of 16-Day NDVI production from 2001 to 2013，the Anomaly Vegetation Index （AVI） was calculated and was used to get the drought frequency，which was the main data in the study of the drought topographic heterogeneity in West Sichuan Plateau，China. What’s more，the DEM and land use/land cover data were got. The former was used to draw the slope and aspect information，which were used as the index of the topography variations to analyze the drought topographic differentiation. The latter was mostly used to do some explanations. The results show as follows：（1）In western Sichuan Plateau，the AVI index method which was frequently used in drought monitoring on the support of Remote Sensing，was also suitable for the drought monitoring in these areas with the altitude below 4 300 m. While in more higher regions，it was not to be the optimum one because of the snow covering disturbances；（2）In the study area，the spatial distribution of drought showed obviously topographic heterogeneity properties，which could be seen from the good linear relationships between the drought frequency and the elevation，so as to the slope and the aspect；（3）The relationship between the drought frequency and the elevation was so complicated，mostly because of the vertical zonality of the land use/land cover variations，besides，the interannual fluctuations of snow line was the other factor of great importance. In relatively lower regions with the elevation below 3 500 m，the variations of vegetation cover played the most important role in the spatial distribution of draught frequency，because different vegetation types had different draught resistance，with the forest land in lower elevation regions taking the first，the wetland and grassland in relatively higher regions followed. While in the regions with the elevation above 3 500 m，the draught frequency was dominated by the interannual fluctuations of the snow line. The elevation of 4 300 m was the average altitude that the influence of seasonal snow cover began to appear. The elevation of 4 716 m was the average elevation that the land cover and seasonal snow cover changed the most dramatically in the annual scale；（4）In different slope gradient，there were good linear relationships between the slope and the draught frequency，with the linear goodness of fit reaching more than 0.9. But in different slope gradients，the linear trend between the slope and the draught varied greatly owing to the different categories of land covers in different slope gradients. The grassland showed highly sensitivity to the draught with the growing of slope，while the forest land was not the case，it showed some stable properties；（5）In different aspects，the draught frequency of the north>northwest>northeast>east>southeast>west>south>southwest. It was mainly due to the stable water vapor source from the south and west of Tibet，the different amount of precipitation in different aspects dominated by the topography，and the difference of ice-snow melt water caused by the uneven distribution of solar radiation. This study had caught some innovations. First，on the point of the drought in high altitude areas，the drought frequency method was firstly used in drought monitoring studies. And moreover，the drought topographic heterogeneity was discussed in the macro scale，further，the reason for the heterogeneities were thoroughly explored.

Key words: drought, topographic heterogeneity, altitude, slope, aspect, AVI