近30a气候变暖对宁夏植被的影响

研究气候变暖对中国北方农牧交错带植被活动的影响,将有助于地方政府在气候变化背景下科学开展植被恢复和生态保护。利用1982—2013年NOAA-VHP数据,基于Mann-Kendall检验、重新标度极差分析和集合经验模态分解等方法,研究了气候变暖对宁夏植被活动的影响。结果表明,宁夏近30 a的辐射亮温增温趋势明显,温度状态指数在1995年前后发生突变,由气候波动期转向持续增暖期;归一化植被指数的线性增长趋势显著(P0.01),上升幅度为0.012/10 a,植被状态指数在1990年前后发生突变,由植被退化转向持续恢复。植被状态指数与温度状态指数的相关性分析得出,在1995年之前气候变暖对宁夏植被活动的影响不明显,但1995年之后气候变暖对宁夏植被活动有明显促进作用,影响强度由强到弱依次是秋季、冬季、春季和夏季;引起这一变化的原因有两点,一是1995年为气候转向暖干的突变点,二是宁夏从20世纪90年代中后期开始实施了一系列的扬黄灌溉开发和生态治理工程,明显地改变了区域植被的分布格局与类型。

Impact of Global Warming on Vegetation Activity in Ningxia Province from 1982 to 2013

Global warming has been proved to be good for plant growth in middle and high latitudes regions in northern hemisphere. However, the responses of vegetation avtivity to climatic changes varies considerably in different ecosystems and regions. Being a typical arid and semi arid area in China, Ningxia Province is located at farming-pastoral ecotone in northern China and has complicated pattern of vegetation cover. Thus, studying on the impact about the vegetation activity in this etfect of global climate changes are of great significance and would help understand the responses of agro-pastoral ecosystem to global climatic changes in northern hemisphere. Based on vegetation health product (VHP) dataset during period of 1982-2013 derived from advanced very high resolution radiometer (AVHRR) on board of national oceanic and atmospheric administration (NOAA) satellites, this study combined methods of Mann-Kendall nonparametric test, rescaled range analysis and ensemble empirical mode decomposition to quantify the impacts of climate warming on vegetation activitives in the study region. The results show that weekly surface brightness temperature (BT) of Ningxia Province significantly increased from 1982 to 2013. An abrupt turning point of weekly temperature condition index (TCI), which is detected by Mann-Kendall nonparametric test, occurred in 1995 when the trend of climatic change shifted from fluctuation to persistent warming. The weekly normalized difference vegetation index (NDVI) increased 0.078/10 a (P<0.01), the speed of which was faster than that in the Three-North Shelter Forest. An abrupt turning point of the weekly vegetation condition index (VCI) was also detected which occurred in 1990. The vegetation activity in Ningxia was degrading before the turing point, while abruptly changed to restore after that. The correlation analysis indicated that there is no significant statistical correlation between VCI and TCI before 1995, which suggested that the climate warming had no obvious impact on vegetation activity in Ningxia Province. However, the significant negative correlation (P<0.01) between VCI and TCI during 1995-2013 suggested that the increase of land surface temperature enhanced the vegetation activity. The impact of climate warming on vegetation activity after 1993 are different in intensity in four seasons, the order from strongest to weakest being autumn, winter, spring and summer. Two main factors were responsible for the change of climate warming’s impact on vegetation activity in 1995: firstly, a abrupt climate change happened in 1995, when the trend of climate changed from fluctuation to continous warming in Ningxia Province; secondly, a series of irrigation projects and ecological restoration projects were implemented by the province goverment, which changed the regional vegetation distribution patterns in the middle and late 1990s. All these changed the main constrain factor of vegetation activity from water to heat.