Spatial and temporal trends of urban green spaces: an assessment using hyper-temporal NDVI datasets

Abstract

Since the last couple of decades urban areas of developing countries have been experiencing unprecedented growth. However, this growth is not well planned in most of the cities. Even in recent days, there is no significant change in city planning and still, there is a lack of concern regarding environmental issues especially the changing green covers in cities. Identifying the green space dynamics of major cities is crucial considering strategic planning of smart cities, policy intervention and combating the problems associated with degreening. The present study attempts to assess the potentiality of hyper-temporal normalized difference vegetation index (NDVI) and its temporal trend as an indicator of greening or de-greening process in Delhi National Capital Territory (NCT) and its peri-urban areas. Ten days composite hyper-temporal SPOT-VGT (Satellite Pour l'Observation de la Terre Vegetation) NDVI images (1998–2013) have been used for identifying the vegetation trend and further, it was compared with long-term CHIRPS (climate hazards centre infrared precipitation with station data) rainfall data to unveil the root causes behind the variation in vegetation trend specifically the contribution of natural and anthropogenic factor in changing scenario of urban green space. The study shows that hyper-temporal NDVI data with sufficient temporal depth can be highly convenient to explore the trend of vegetation and changes in green space. The spatio-temporal pattern of NDVI trend indicates a significant part of the area including Noida, Gurgaon etc. experienced decreasing vegetation trend which can be explained by large scale conversion of vegetated land into built-up areas due to establishment of new multi-storied buildings. The strong negative correlation (r ≤ − 0.8) between rainfall-NDVI indicates that rainfall is not the major controlling factor of vegetation trend in that area rather anthropogenic activities played a significant role in depletion of vegetation. During 1998–2013, the areas of bounding zone have been largely converted into built-up area and as a consequence, surface vegetation cover of these areas has been depleted. However, human induced greening was also observed in small pockets of Delhi NCT that can be explained by the impact of positive measures like tree plantation and proper maintenance of urban trees along roads, parks, and gardens.