(a) Sequential changes in land use and land cover have brought global and regional ecological changes and imbalances. Elucidate…

(a) Sequential land-use and land-cover change

Sequential land-use and land-cover change usually moves from forest or grassland clearance to agriculture, then to urbanisation, and in some regions to reforestation or land abandonment, as forest transition theory describes. Each stage alters biophysical processes. Deforestation in the Amazon reduces evapotranspiration, lowers local rainfall, releases stored carbon, fragments habitats and increases fire risk, while Sahel desertification shows how overgrazing, cropping and reduced vegetation cover can push drylands toward irreversible thresholds. In India, Green Revolution expansion in Punjab changed water tables, soil salinity and cropping patterns, while Delhi NCR sprawl has replaced green cover with impervious surfaces, raising runoff, heat-island effects and air pollution. These changes disrupt the carbon cycle by converting living biomass and soils into CO2 sources, reduce biodiversity through habitat loss and fragmentation, and alter hydrology by changing infiltration, baseflow and flood peaks. Feedbacks compound the imbalance: lower evapotranspiration reduces moisture recycling, albedo changes affect local energy balance, and soil degradation lowers productivity and increases erosion. Indicators such as declining vegetation cover, waterlogging, salinisation, siltation, altered streamflow and species loss show that land systems can cross tipping points, making ecological recovery difficult.

(b) Channel morphology in planning and flood management

Channel morphology—width-depth ratio, sinuosity, gradient, bank strength and discharge patterns—directly shapes engineering and planning decisions. A wide, shallow, braided channel such as the Kosi, which is avulsion-prone rather than simply meandering, requires broad floodplain zoning, flexible embankment alignment and avoidance of permanent settlements in active braid belts, as the 2008 Kusaha breach of the Kosi showed. The Brahmaputra’s variable sinuosity and wide, shallow reaches influence bridge span design, approach embankments and the siting of towns away from cut-bank erosion. In the Narmada, a comparatively straight, incised channel with lower floodplain width allows different settlement patterns and controlled embankments, but steep valley sides still constrain transport corridors. For transportation, sinuosity and gradient determine bridge length, navigation channels and road alignment; for flood control and management, channel capacity and bankfull discharge guide embankment height, spillway locations and drainage design; for land use planning, floodplain zoning uses historical channel migration, avulsion frequency and inundation depth to separate residential, agricultural and industrial uses, the approach of the Model Bill for Flood Plain Zoning (1975).

(c) Ocean currents, winds and gyres

Surface ocean currents are mainly wind-driven. Trade winds push equatorial waters westward, while mid-latitude westerlies drive eastward currents; the Coriolis effect deflects moving water to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. In the surface layer, wind stress and Coriolis balance produce a surface current at about 45 degrees to the wind, while the integrated Ekman transport is directed about 90 degrees to the right of the wind in the Northern Hemisphere and to the left in the Southern Hemisphere. This transport piles water into subtropical gyres, creating pressure gradients that generate geostrophic flow. In the Northern Hemisphere, subtropical gyres rotate clockwise and subpolar gyres rotate counter-clockwise; western boundary currents such as the Gulf Stream and Kuroshio are intensified, narrow and fast. In the Southern Hemisphere, subtropical gyres rotate counter-clockwise, and subpolar gyres such as the Weddell and Ross gyres are less confined by land and strongly modified by the Antarctic Circumpolar Current. Because the Antarctic Circumpolar Current links all three oceans, the southern gyres are not closed by land on their poleward side. Western boundary currents are therefore less uniform: the Agulhas Current is the strongest, the Brazil Current is comparatively weak, and the East Australian Current breaks into large eddies, showing how basin shape and wind stress create hemispheric asymmetry.