黑河下游绿洲NDVI对地下水位变化的响应研究

本研究选取黑河下游核心绿洲区作为研究区域，通过对绿洲区植被变化和地下水位的长期监测，分析黑河下游绿洲植被与地下水位的关系；通过表面分析以及空间分析方法，探讨地下水位变化对绿洲植被的分布格局的影响，揭示绿洲植被变化对地下水位的响应。结果表明：额济纳地区2001年归一化植被指数(NDVI)值整体上小于1990年NDVI值，植被生长状况较1990年差；2009年河道附近绿洲区局部NDVI值增加，但大部分NDVI值仍小于1990年。相较2001年，2009年西河中上段河道附近植被有明显改善，西河下段植被仍呈现退化趋势，这主要与东西河分水措施有直接关系；东河上段河道附近绿洲呈现明显好转，东河中段变化不大，而东河下段植被面积略微增加，东居延海周围植被明显好于2001年。通过比较1990年、2001年和2009年地下水位与NDVI值的关系发现，地下水较为适宜的水位仍保持在2~4 m之间，地下水位下降与植被退化或者植被盖度降低有直接关系。

Response of NDVI to Groundwater Level Change in the Lower Reaches of the Heihe River, China

The core oasis in the lower reaches of Heihe River is selected as a study area. Through long-term monitoring the oasis vegetation change and the oasis groundwater level, the relationship of vegetation cover and the groundwater level in the lower reaches of Heihe River oasis is analysed. The surface analysis and spatial analysis methods are used to discuss how the groundwater level change influenced the distribution pattern of the oasis vegetation. Results showed that NDVI values in 2009 were wholelly smaller than in 1990 in the lower reaches of Heihe River. The vegetation growth in 2009 as a whole was worse than in 1990. The local NDVI values near river increased in 2009, but most of the NDVI values were still less than in 1990. Compared with that in 2001, the vegetation near West River upper and mid reaches significantly improved in 2009, but the vegetation in West River lower reaches still showed a degradation trend. The vegetation cover near upper reaches of East River presented significant improvement, vegetation cover changed little in the mid reaches of East River, vegetation cover area showed a slight increase in the lower reaches of East River, but vegetation cover had not yet reached the level in 2001. The vegetation cover surrounding East Juyanhai Lake in 2009 was better than in 2001. Comparison of the relationship between groundwater depth and vegetation cover in 1990, 2001 and 2009 showed that the suitable groundwater depth for vegetation was still at 2-4 m. There were direct relations between groundwater level falling and vegetation degradation.