(a) What are the causes of origin of local winds? Discuss their significance on prevailing weather and climate in various…

(a) Origin and significance of local winds

Local winds are small-scale circulations, too limited in size to appear in the planetary wind belts. They arise from three groups of causes.

(i) Differential heating. Land and water, or sunlit and shaded slopes, heat and cool at different rates, giving sea and land breezes and mountain and valley breezes. The Loo, a hot dry afternoon wind of north-west India and Pakistan, arises from intense summer heating of the plains.

(ii) Relief. Air forced over a range cools on the windward side and descends warm and dry on the lee side, as the Chinook of the Rockies, the Foehn of the Alps and the Santa Ana of California. Cold air drains down slopes as the Mistral in France and the Bora on the Adriatic.

(iii) Pressure systems. Local pressure gradients move air from desert or cold areas, giving the Harmattan, Sirocco and Khamsin.

Significance. (i) The Chinook melts snow in a few hours, extending the grazing season, but can cause floods. (ii) The Santa Ana, hot and dry, dries vegetation and spreads wildfire. (iii) The Loo raises temperatures past 45 °C, causing heat stress and drought. (iv) The Mistral and Bora bring cold snaps, and orchards need windbreaks against them. (v) Kal Baisakhi, the pre-monsoon squall of Bengal and Assam, gives thunderstorms helpful to tea, jute and rice. (vi) The Sirocco carries Saharan dust to southern Europe. (vii) Sea breezes cool the coast and trigger afternoon showers. Together they modify temperature, humidity and rainfall, and shape agriculture, fire risk and settlement.

(b) Peneplains and associated landscapes

A peneplain is a nearly flat, gently undulating erosion surface reduced close to base level after a long period of denudation.

(i) Davisian cycle. It is the end product of the old-age stage. After youth, with steep valleys, and maturity, with graded rivers, the old-age landscape shows wide shallow valleys, meandering rivers with oxbows, marshes, and low divides. Isolated residual hills called monadnocks stand above it, such as Mount Monadnock in New Hampshire.

(ii) Penckian cycle. Penck held that slopes retreat in parallel, leaving a gently rolling surface called the Endrumpf, with piedmonttreppen (stepped slopes) in between. Uplift rate against denudation decides the form.

(iii) Other cycles. In arid and semi-arid regions King's pedimentation produces pediplains with inselbergs, while deep chemical weathering in the humid tropics leaves etchplains.

(iv) Rejuvenation. Uplift, a fall in sea level or tilting renews erosion, giving river terraces, entrenched meanders and dissected peneplains, as in the peninsular plateau of India.

The landform thus shows low relief, meanders and monadnocks, though its form depends on the cycle.

(c) Regional ecological change and human health

The factors fall into three groups.

(i) Natural. Climatic change, shifts in rainfall, droughts, floods, cyclones and volcanic eruptions alter vegetation and water.

(ii) Biotic. Invasive species, outbreaks of pathogens, and succession of vegetation change a region's community.

(iii) Human. Deforestation, urban growth, land-use change, dams, mining, pollution and intensive farming change habitats, water and nutrient cycles.

Effects on health.

(i) Direct. Air pollution causes respiratory disease, contaminated water causes diarrhoea and cholera, urban heat islands cause heat stroke, and chemical contamination causes cancers and poisoning.

(ii) Indirect. Warmer and wetter conditions extend vector-borne diseases such as malaria, dengue and chikungunya to new areas. Loss of crops and ecosystem services causes malnutrition, and disasters and displacement cause mental stress.

(iii) Examples. The spread of dengue in Indian cities, and arsenic in the groundwater of West Bengal and fluoride in Rajasthan, show the link.

Managing these needs pollution control, sustainable land use, disaster preparedness, health surveillance and climate adaptation together.