The rapid expansion of urban built environments in India's big cities profoundly alters the biophysical character of the landscape, transforming natural systems into human-dominated ones. These changes have significant ecological and environmental consequences:

1. Land Use and Land Cover Change: The most direct impact is the conversion of natural landscapes (forests, wetlands, agricultural land, open spaces) into impervious surfaces like concrete, asphalt, and buildings. This leads to habitat loss, fragmentation of ecosystems, and a reduction in biodiversity, as native flora and fauna are displaced or perish.

2. Urban Heat Island (UHI) Effect: Built materials like concrete and asphalt absorb and retain more solar radiation than natural surfaces, leading to significantly higher temperatures in urban areas compared to surrounding rural areas. This 'urban heat island' effect increases energy consumption for cooling, exacerbates air pollution, and impacts human health.

3. Altered Hydrology: Impervious surfaces prevent rainwater infiltration into the ground, reducing groundwater recharge and increasing surface runoff. This heightened runoff can overwhelm drainage systems, leading to urban flooding, especially during heavy rainfall. Natural water bodies are often encroached upon, polluted, or replaced by artificial drainage channels.

4. Air and Water Pollution: Urbanization concentrates sources of pollution. Vehicular emissions, industrial activities, and domestic waste contribute to severe air pollution (particulate matter, NOx, SOx). Untreated or partially treated sewage and industrial effluents contaminate rivers, lakes, and groundwater, impacting aquatic ecosystems and human health.

5. Biodiversity Loss: Habitat destruction, pollution, and human disturbance directly lead to a decline in native plant and animal species. Urban areas often become dominated by a few adaptable or invasive species, further reducing ecological diversity.

6. Soil Degradation: Construction activities involve extensive excavation, compaction, and removal of topsoil, leading to soil erosion and reduced soil fertility. Urban soils are also often contaminated with heavy metals and other pollutants.

7. Microclimate Modification: Tall buildings and dense urban structures alter wind patterns, creating wind tunnels or sheltered areas. Changes in surface albedo and evapotranspiration also modify local humidity and precipitation patterns.

In essence, the urban built environment fundamentally re-engineers the natural landscape, creating a distinct anthropogenic ecosystem with altered energy flows, material cycles, and ecological processes. Understanding and mitigating these biophysical changes through sustainable urban planning is crucial for the long-term environmental health and liveability of Indian cities.