陕北地区植被指数对水热条件变化的响应及其时滞分析

Response of NDVI to Temperature and Precipitation Changes and Its Lag Time in North Shaanxi

采用时滞互相关法,利用陕北地区1999-2010年旬平均温度、降水数据和SPOT-NDVI数据,分析植被覆盖对水热条件的年内时滞响应.结果表明：（1）陕北南部植被覆盖较好,NDVI平均值（TN）与旬平均温度（TT）、旬降水量（TP）的相关程度高,相关系数在0.9以上,响应迅速,滞后时间为1～2旬;而地处毛乌素沙漠南缘的风沙草滩区,TN与TT、TP的相关程度相对较低,相关系数在0.75～0.85,响应时间也相对较长,多数区域滞后时间为3～5旬.说明水热条件好的区域相关程度高且响应迅速,而水热条件差的区域相关程度低且响应较慢.从不同生态亚区来看,盆地和黄土塬梁沟壑区对水热因子的综合响应程度比黄土丘陵沟壑亚区及典型草原生态亚区高.（2）气温年内变化对植被NDVI的影响程度从南向北逐渐减小,南部密集灌丛与TT的相关系数最大,为0.947,北部沙漠区最小,为0.902.降水量年内变化对植被NDVI的影响中以耕地为最大,平原草原和低山草原次之,沙漠区最小.耕地NDVI与TP的相关系数为0.926,沙漠的为0.853.与气温的相关程度高且响应快的植被,其生长对温度的要求也高,相关程度低且响应慢的植被,其生长对气温的要求也低.植被对年内降水的响应与温度相似.研究结果可为陕北地区优化植被种植类型提供理论依据.

Based on ten -day average temperature, precipitation and ten -day NDVI of SPOT data from 1999 to 2010 in north Shaanxi, annual responses of vegetation cover to temperature and precipitation was analyzed by using of the lag cross -correlation method. The results showed that there was strong correlation between NDVI and temperature and precipitation, with the correlation coefficient more than 0.9. The response was promptly over south of Shanbei, with the lag time only ten to twenty days. The correlation coefficient was between 0. 75 -0. 85 across the Maowusu desert sand grass land area, with the lag time thirty to fifty days. NDVI showed a greater correlation and faster response to areas with much water and high temperature. From other perspective, the comprehensively responses to water and thermal factor on basin, loess tableland beam and gully region was better than the gullies rolling loess sub-area and typical grassland ecological subregions. The effect degree of temperature on NDVI decreased gradually from south to north, the max correlation coefficient was 0. 947 between bush and temperature, and minimum correlation coefficient was 0. 902 in desert. The effect degree of precipitation on NDVI was maximum in farmland, followed by plain grassland and low mountain grassland, and minimum in desert. The correlation coefficient was 0. 926 between farmland and precipitation, and 0. 853 in desert. A certain type of vegetation required a higher temperature, also had faster response than others. On the contrary, vegetation depended on low temperature vegetation cover to annual precipitation for optimizing vegetation planting types was similar to that in north Shaanxi of temperature. also showed slow response. The response of The results could provide a theoretical basis