Assessment of Changes in Land Use/Land Cover and Land Surface Temperatures and Their Impact on Surface Urban Heat Island Phenomena in the Kathmandu Valley (1988-2018)
Assessment of Changes in Land Use/Land Cover and Land Surface Temperatures and Their Impact on Surface Urban Heat Island Phenomena in the Kathmandu Valley (1988-2018)
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DOI：
10.3390/ijgi9120726
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发表时间：
2020-12-01
影响因子：
3.4
通讯作者：
Stork, Nigel E.
中科院分区：
文献类型：
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作者：
Sarif, Md Omar;Rimal, Bhagawat;Stork, Nigel E.
世界上一半以上的人口现在生活在迅速扩大的城市及其周边地区。许多新兴城市对土地利用/土地覆盖（LULC）动态和地表城市热岛（SUHI）现象的影响知之甚少。我们利用1988年、1998年、2008年和2018年的4月（夏季）Landsat图像，以10年为间隔，在加德满都谷地（面积约694公里）探讨了这一问题及其相互关系。采用支持向量机算法进行LULC评价。在加德满都谷地，大部分土地是自然植被或农业用地，但在研究期间，城市地区的不透水地表迅速扩大。1988-2018年，不透水地表面积增加113.44 km(2)，占总面积的16.34%，自然植被面积增加6.07 km(2)，占总面积的0.87%，导致农业用地面积减少118.29 km(2)，占总面积的17.03%。与此同时，城市平均地表温度（LST）上升了近5 ~ 7℃，城市边界上升了近3 ~ 5℃。在不同的LULC类别中，1988-2018年期间，IL的平均温度增幅最高，为7.11℃，VL的平均温度增幅最低，为3.18℃，尽管这段时间内存在一些波动。虽然开阔地仅占景观的一小部分，但其平均地表温度通常高于其他所有类型的地表温度。地表温度与植被正差指数（NDVI）、水汽正差指数（NDMI）呈负相关，与建筑正差指数（NDBI）呈正相关。城乡梯度分析结果显示，由于NDVI也急剧增加，从城市中心向外的平均地表温度急剧减少至约15 km，特别是在2008年和2018年，地表热岛效应明显。在离市中心更远的20-25公里处，由于农业活动增加，平均地表温度增加。2016年加德满都谷地的人口为288万，如果这一增长趋势继续下去，预计到2035年将达到385万。因此，为了避免加德满都增加SUHI的关键影响，必须改进城市规划，包括实施绿色城市技术。
More than half of the world's populations now live in rapidly expanding urban and its surrounding areas. The consequences for Land Use/Land Cover (LULC) dynamics and Surface Urban Heat Island (SUHI) phenomena are poorly understood for many new cities. We explore this issue and their inter-relationship in the Kathmandu Valley, an area of roughly 694 km(2), at decadal intervals using April (summer) Landsat images of 1988, 1998, 2008, and 2018. LULC assessment was made using the Support Vector Machine algorithm. In the Kathmandu Valley, most land is either natural vegetation or agricultural land but in the study period there was a rapid expansion of impervious surfaces in urban areas. Impervious surfaces (IL) grew by 113.44 km(2) (16.34% of total area), natural vegetation (VL) by 6.07 km(2) (0.87% of total area), resulting in the loss of 118.29 km(2) area from agricultural land (17.03% of total area) during 1988-2018. At the same time, the average land surface temperature (LST) increased by nearly 5-7 degrees C in the city and nearly 3-5 degrees C at the city boundary. For different LULC classes, the highest mean LST increase during 1988-2018 was 7.11 degrees C for IL with the lowest being 3.18 degrees C for VL although there were some fluctuations during this time period. While open land only occupies a small proportion of the landscape, it usually had higher mean LST than all other LULC classes. There was a negative relationship both between LST and Normal Difference Vegetation Index (NDVI) and LST and Normal Difference Moisture Index (NDMI), respectively, and a positive relationship between LST and Normal Difference Built-up Index (NDBI). The result of an urban-rural gradient analysis showed there was sharp decrease of mean LST from the city center outwards to about 15 kms because the NDVI also sharply increased, especially in 2008 and 2018, which clearly shows a surface urban heat island effect. Further from the city center, around 20-25 kms, mean LST increased due to increased agriculture activity. The population of Kathmandu Valley was 2.88 million in 2016 and if the growth trend continues then it is predicted to reach 3.85 million by 2035. Consequently, to avoid the critical effects of increasing SUHI in Kathmandu it is essential to improve urban planning including the implementation of green city technologies.