Spatial and Temporal Dynamics of Urban Wetlands in an Indian Megacity over the Past 50 Years

Abstract

Asian megacities have attracted much scientific attention in the context of global urbanization, but few quantitative studies analyze wetland transformation in the rural–urban interface. With its rampant growth and transformation from a tree-lined “Garden City” to a busy megalopolis with often-blocked highways and large built-up areas, Bengaluru (Karnataka, S-India) is a good example for assessing how urbanization has led to the acute degradation of wetlands. We therefore investigated long-term land cover and wetland changes from 1965 to 2018 based on an object-based classification of multi-temporal Corona and Landsat images. To quantify and compare the dynamics of open water surfaces and vegetation, we defined the potential wetland areas (PWA) along the rural–urban gradient and linked our analyses to an index describing the degree of urbanization (survey stratification index (SSI)). During the five decades studied, built-up areas in the Bengaluru Urban district increased ten-fold, with the highest growth rate from 2014 to 2018 (+ 8% annual change). Patches of lake wetlands were highly dynamic in space and time, partly reflecting highly variable annual rainfall patterns ranging from 501 mm in 1965 to 1374 mm in 2005 and monsoon-driven alterations in the hydrologic regime. While water bodies and flooded areas shrunk from 64 km2 in 1965 to 55 km2 in 2018, in 1965, the total rural wetland area with an SSI > 0.5 was twice as high as in 2018. The rural–urban land cover pattern within potential wetland areas changed drastically during this period. This is reflected, for example, by a four-fold increase in the wetland area with an SSI of 0.3, as compared to a decline by 43% in wetland area with an SSI of 0.8. While, in urban areas, wetlands were mostly lost to construction, in areas with a rural character, open water bodies were mainly transformed into green space. The detected changes in urban wetlands were likely accompanied by ecological regime changes, triggering deteriorations in ecosystem services (ESS) which merit further research.

Introducing GEOBIA to Landscape Imageability Assessment: A Multi-Temporal Case Study of the Nature Reserve “Kózki”, Poland

“…Similar to other cases of historical imagery pre-processing [66], metadata like interior and exterior camera orientation (applied to aerial imagery) were unknown. Therefore, we applied the image to an image co-registration technique [14,[67][68][69], as an alternate method known to yield satisfactory results especially in low-relief terrains [70]. A highresolution (GSD 0.25 m, horizontal accuracy 0.15 m) contemporary orthoimage [71] was used as a reference to conduct co-registration.…”

“…Taking advantage of image object geometry, texture, and brightness, we adopted the Reference [67] framework of combining manual and supervised image object classification, along with post-processing procedures. Firstly, water bodies and building footprints were manually digitized (on-screen visual interpretation) and incorporated as classified segments into an MRS workflow.…”

Water Use in Human Civilizations: An Interdisciplinary Analysis of a Perpetual Social-Ecological Challenge

“…However, the pace of planning and execution to pump Kaveri water in different phases has not been able to keep up with the rapid growth. Importantly, filling in of tanks and lakes for construction, sedimentation, and blockage of natural drainage in and around the city area have contributed to the shrinking of lakes [78] and overall declining surface water sources for agriculture that met urban needs for perishable goods. As a result of a typical red loop situation [79] , for the past 50 years much of the drinking and irrigation water for agriculture, global flower production, and beautification of the city has been drawn from deep tube wells.…”

Land Consumption and Land Take: Enhancing Conceptual Clarity for Evaluating Spatial Governance in the EU Context

“…However, according to the methodology for calculating the EU land take indicator, this includes wetlands, and the conversion of waterbodies to urban area is also counted as land take (see Section 3.2). While only a small fraction of the total land take affects wetlands and waterbodies in Europe (with exceptions in some countries, e.g., in Iceland or The Netherlands) [32], urbanization has a huge impact on waterbodies in some other parts of the world (examples include the expansion of some of the Asian megacities) [65]. The land take concept thus bears potential for wetlands as well.…”