Change of remote sensing ecological index of an oasis city in the arid area
ZHOUXuande1,, GUOHuadong2, Zibibula·Simayi3,, DENGZutao1, LIANGBin1 1. School of Tourism and Hospitality Management, Hubei University of Economics, Wuhan 430205, China2. Key Laboratory of Digital Earth, Center for Earth Observation and Digital Earth, CAS, Beijing 100094, China3. College of Resource and Environmental Science of Xinjiang University, Urumqi 830046, China 通讯作者:通讯作者:孜比布拉·司马义,E-mail: zibibulla3283@sina.cn 收稿日期:2018-07-19 修回日期:2019-04-12 网络出版日期:2019-05-25 版权声明:2019《资源科学》编辑部《资源科学》编辑部 基金资助:国家自然科学基金项目(41661036)国家社会科学基金项目(14BJY225;15BJY128) 作者简介: -->作者简介:周玄德,男,安徽宿州人,博士,讲师,主要研究方向:资源利用与城乡规划。E-mail: zxd850706@163.com
关键词:城市生态;遥感;生态指数;景观;干旱区绿洲;乌鲁木齐市 Abstract Xinjiang Uyghur Autonomous Region is a typical arid area, and its ecological environment is extremely fragile. It is of great significance to understand its ecological environment changes in a timely and accurate manner.This study chose the oasis city Urumqi in Xinjiang as the research area and used the remote sensing images from the same month of 2004 and 2016 to calculate the remote sensing ecological index (RSEI), and analyze the present situation, spatial distribution, center of gravity, landscape features, and driving factors of change of RSEI. The results show that: (1) In 2004—2016, the average remote sensing ecological index value increased from 0.341 to 0.400, an increase of 17.24%. Normalized Difference Vegetation Index (NDVI), Wetness (WET), and Land Surface Temperature (LST) showed a certain degree of increase, and Normalized Difference Build-up Soil Index (NDBSI) showed a downward trend; (2) With the classification of ecological index values, the main part of the study area fell within poor and medium ecological index classes. The total area of these classes is obviously growing.The classes mainly remained unchanged or improved, and the areas with improvements of ecological index mainly moved up for one class; (3) The center of gravity of all types of ecological index classes shifted, and the distance of gravity center shift of the poor ecological index class was the longest, reaching 2.82 km. The distance of shift was relatively small for other classes; (4) Landscape pattern of different types of remote sensing ecological indices changed, complexity of shape of patches increased, the spatial connectivity and agglomeration were significant.This study analyzed the spatial characteristics and changes of the ecological index and found that the process of gradual change of the ecosystem under the premise of maintaining stability with human activities is closely related to urban expansion.
乌鲁木齐市位于中国西北,为新疆维吾尔自治区的首府,新疆经济、社会、文化中心,也是天山北坡经济带的中心,在新疆的经济发展中具有非常重要的作用。然而由于典型的温带大陆干旱性气候,水资源匮乏、生态环境脆弱等问题对乌鲁木齐市的发展带来了巨大挑战。本文以乌鲁木齐市人类活动剧烈的主城区作为研究对象,范围为87°27′3″E—87°43′15″E,43°44′20″N—43°58′1″N,总面积540.65 km2(图1),通过对其生态时空变化特征进行分析,可为干旱区绿洲城市生态调控发挥指导借鉴作用。 显示原图|下载原图ZIP|生成PPT 图1研究区位置 -->Figure 1Location of the study area in Urumqi City -->
根据上述的研究方法,获得2个年份的指标的统计值,见表2。研究发现,2004年研究区RSEI的均值为0.341,2016年达到了0.400,增长17.24%,表现为研究区的生态指数向好的趋势发展。从图2中也可以发现,在研究区的周边区域生态指数有了明显的改善,该区域2004年生态指数相对较低,2016年该区域的生态环境质量有了很大的提升,从而带动了整个研究区生态环境质量整体水平的提高。 Table 2 表2 表2乌鲁木齐市遥感生态指数及相关指标统计值 Table 2Remote sensing ecological index and related indicator value statistics, 2004 and 2016
2004年
2016年
最小值
最大值
均值
标准差
最小值
最大值
均值
标准差
NDVI
-0.540
0.809
0.219
0.163
-0.383
0.769
0.264
0.143
WET
-0.627
0.071
-0.138
0.053
-0.848
0.155
-0.039
0.042
LST
19.333
49.749
38.365
3.680
25.540
52.903
40.906
2.806
NDBSI
-0.502
0.386
0.115
0.091
-0.360
0.504
0.111
0.081
RSEI
0.000
1.000
0.341
0.165
0.000
1.000
0.400
0.140
新窗口打开 显示原图|下载原图ZIP|生成PPT 图2乌鲁木齐市遥感生态指数空间分布 -->Figure 2Spatial distribution of remote sensing ecological index values, 2004 and 2016 -->
为了更加深入地分析研究区生态指数RSEI的空间变化,参照前人的相关研究[10],将RSEI按照0.2的间隔,划分为5个等级,包括生态指数低(0.0~0.2)、生态指数较低(0.2~0.4)、生态指数中等(0.4~0.6)、生态指数较高(0.6~0.8)、生态指数高(0.8~1.0),同时为了使用方便给予编号,依次标为A、B、C、D、E,具体计算结果见图3和表3。研究区的生态指数高值区集中在城市中心,低值区主要分布在城市周边区域,其中西北农田区域生态指数一直较高,生态环境较好。 显示原图|下载原图ZIP|生成PPT 图3乌鲁木齐市遥感生态指数的等级分布 -->Figure 3Spatial distribution of remote sensing ecological index value classes, 2004 and 2016 -->
Table 3 表3 表3乌鲁木齐市遥感生态指数各等级面积及占比 Table 3Percentage of areas of remote sensing ecological index value classes, 2004 and 2016
RSEI等级
2004年
2016年
面积/km2
百分比/%
面积/km2
百分比/%
A
90.04
16.65
7.53
1.39
B
301.90
55.84
312.51
57.80
C
93.40
17.28
165.92
30.70
D
48.19
8.91
46.78
8.65
E
7.12
1.32
7.91
1.46
合计
540.65
100.00
540.65
100.00
新窗口打开 2004年,研究区周边被大面积的生态指数低的区域所覆盖;向城市中心方向,生态指数在逐渐上升,但生态指数中等及以上的区域也只是零散的分布。 2016年,大面积的生态指数低值区域得到提升,特别是研究区的西部、东部区域;同时在城市中心,生态指数在中等以上水平区域连片出现,生态指数高值区域也明显增多。由此说明,研究区生态指数表现为变好。 表3给出了研究区生态指数各等级面积及占比。2004年,生态指数为A级的区域面积90.04 km2,占比16.65%,到2016年,该类面积仅7.53 km2,占比1.39%,下降幅度非常大,说明了生态环境差的区域在大面积消失、变好;生态指数为B级的区域在整个研究区占绝大比重,2004年该类面积301.90 km2,占总面积的55.84%,到2016年该类增加了10.61 km2,占比57.80%,变化幅度不大;生态指数为C级的区域的面积从2004年的93.40 km2增长到165.92 km2,占比从17.28%增至30.70%,增幅显著;生态指数在D、E级的区域面积较小,占比较低,将其合并计算时,两者面积从2004年的55.31 km2变化为54.70 km2,相应占比从10.23%变为为10.12%,基本处于稳定。研究区各类等级的生态指数的统计值表明生态环境正在得到改善,但从比例来看整个研究区的生态指数依然仍以较低和中等水平为主,2016年两者占总面积的88.49%;生态指数为较高和高等级的面积较小,因而整体的生态环境水平仍不高。 为进一步分析研究区生态指数的变化特征,对2个时相的生态指数进行比较,从下降、不变、上升3个层面进行分类,得出研究区生态指数空间变化图(图4)。研究发现:生态指数不变区主要集中在城市的中心区,与城市的建成区重叠度较高;生态指数下降区主要分布在城市的郊区、外围;生态指数上升区域多位于城市中心与郊区的过渡带。 显示原图|下载原图ZIP|生成PPT 图4乌鲁木齐市遥感生态指数等级变化 -->Figure 4Spatial change of remote sensing ecological index value classes in Urumqi City, 2004—2016 -->
表4分别对各等级的具体变化情况进行统计。结果显示,2004年以来,研究区有259.84 km2的区域生态指数维持原状,占总面积的48.06%;生态指数等级处于下降的区域面积71.70 km2,占总面积的13.26%,其中69.96%的区域生态指数下降1个等级;生态指数等级上升的区域209.12 km2,占总面积的38.68%,其中82.60%的区域生态指数上升1个等级。因此,研究区生态指数的变化主要集中1个等级范围内,表明整个城市生态系统在近13年来相对稳定,并没有出现大范围生态环境恶化的现象,总体向好的趋势发展。 Table 4 表4 表4乌鲁木齐市生态指数面积变动情况 Table 4Change of ecological index classes in Urumqi City
前文将研究区整体的生态指数划分为5类,即研究区由5类生态指数构成。为研究各类要素的重心转移变动情况,利用ArcGIS 10,将5类要素转化为矢量点,分别计算各类要素的重心,分析其在2004年和2016年的位置变动情况,计算结果如图5所示。 显示原图|下载原图ZIP|生成PPT 图52004—2016年乌鲁木齐市不同生态指数区域的重心偏移 -->Figure 5Shift incenter of gravity of various ecological index classics in Urumqi City, 2004-2016 -->
许多研究表明[10,31],以NDVI为代表的绿度和以WET为代表的湿度对生态指数起正面影响,以LST为代表的热度和以NDBSI为代表的干度对生态指数起负面作用。这与本文结果相一致。本文中与生态环境呈正相关的绿度对生态指数的贡献度增大,可能与2016年乌鲁木齐市新建街旁绿地、绿道[22],在道路、广场、交通环岛等重要节点摆放花卉,增加地表植被面积密切相关。 本文从整体区域出发,得出了研究区中心区域生态质量稳定、远郊区域生态质量较差、近郊区域生态质量优化明显的结论。该结论也从侧面印证了城市发展状态。城市中心主要被大量的道路、建筑所覆盖,现状相对较稳定,生态系统相对均衡,并维持着一定的水平。伴随城市化的扩张,建成区向外扩张,扩张区域将承担部分城市功能,特别是人类居住的功能。城乡结合部原本生态指数较低,经过新型城镇发展规划后,通常对园林绿化、生态环境质量更为重视,体现出生态指数升高的趋势。而远郊区原本农田或自然植被占很大比重,经过城市的不断扩张,原有植被遭到破坏,使其生态指数降低。 结合研究区生态指数的空间变化,可以发现生态指数随着人类活动逐渐演变。生态系统在维持内部稳定性的同时,人类活动一方面可起到改善生态环境作用,如研究区中部偏东的集中连片的变好区域主要由于植被恢复措施的作用;另一方面随城市的扩展给生态环境带来压力,如研究区西北部大面积生态指数下降,主要由于城市化过程中农田面积被侵占、建设用地增加所致。 乌鲁木齐市是新疆的首府,为政治、经济中心,人口从2004年的235万人增长到2016年的352万人,国内生产总值相应地从478亿元增长到2459亿元,。国内外已有研究表明,经济、农业生产水平的提高,生活方式的转变以及劳动力转移都可能影响到生态环境的变化[32,33]。综上分析,生态环境的变化是多种因素共同作用的结果。 在研究方法上,本文立足于研究区2期遥感生态指数空间分布对比分析,揭示研究区生态环境现状及空间分布特征,探讨了生态环境的空间变化规律,并尝试从生态指数类型的视角分析景观格局特征,从而进一步细化了生态环境的变化研究,一定程度上弥补了现有研究在景观格局分析上的不足。但由于本文仅选取2年数据,对生态环境演变的分析上略显单薄,今后应在更加深入开展城市遥感生态研究的基础上,深层次挖掘城市生态环境好转的影响因素,同时结合人类活动的变化规律,寻求人与自然的和谐共处。 The authors have declared that no competing interests exist.
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