多尺度下宝鸡地区干旱动态格局演变及其与植被覆盖的关系

利用宝鸡地区11个气象站点1974—2013年逐月气温和降水量数据,基于标准化降水蒸散指数(SPEI),结合土地利用/覆盖数据,从干旱发生频率、发生强度及与植被NDVI相关性等角度,探讨了近40年来干旱时空变化格局及其对植被覆盖的响应。结果显示:宝鸡地区年均SPEI指数以-2.50%/a的速度下降,干旱趋势明显增强。自20世纪末以来,全区年均干旱指数呈明显的上升趋势,以2007—2010年增大趋势最为显著(超过0.05临界线);近40年来,春季干旱发生频率达60%及以上的有21 a,达90%以上的有9a。1981—1986年起伏变化最为剧烈。秋季平均干旱发生频率为46.29%,为春、夏、秋、冬4个季节中最低。从干旱发生强度来看,全区年际、四季及月6个时间尺度上干旱强度高、低值区域分布均比较集中;秋季强度最弱的区域面积表现最高,占总面积的75.47%。干旱发生最严重的是春季,占总面积的11.90%。全区干旱与植被覆盖相关性均表现较好(均通过0.05显著性水平检验),林地、草地负相关性最为显著(除夏季),夏季、秋季、月尺度上,耕地、水域、城乡地区干旱与植被覆盖的相关性与土地利用类型无关。

Study of dynamic pattern evolution of drought and its correlation with vegetation cover in Baoji area on multi-scale

Using the monthly temperature and precipitation data from 11 meteorological stations in Baoji area from 1974 to 2013, based on the Standardized Precipitation Evapotranspiration Index (SPEI) and combined with land use/land cover data. The temporal and spatial variation pattern of drought and its response to vegetation cover in the last 40 years were discussed from the angles of drought occurrence frequency, occurrence intensity and correlation with vegetation NDVI. The results showed that the average annual SPEI index of Baoji area decreased by 2.50 percent year, and the drought trend was significantly enhanced. Since the end of 20th century, the average annual drought index in the whole region has shown a marked upward trend, especially in 2007 to 2010 (above the 0.05 critical line). In the past 40 years, the frequency of spring drought has reached 60% and above in 21 years, and more than 90% in 9 years, from 1981 to 1986, the fluctuation was the most severe. The average frequency of drought in autumn was 46.29%, which was the lowest in spring, summer, autumn and winter. From the intensity of drought, the high and low value area of drought intensity per year, spring, summer, autumn, winter and month at six time scales were relatively concentrated. The area with the weakest intensity in autumn was the highest, accounting for 75.47% of the total area. The most serious drought occurred in spring, accounting for 11.90% of the total area. The correlation between drought and vegetation coverage in the whole region was better (all through 0.05 significant levels). The negative correlation between forestland and grassland was the most significant (except summer). In summer, autumn and monthly scale, the correlation between drought and vegetation cover in cultivated land, water area, urban and rural areas is not related to land use type.