Relief and climate in South Asia: the influence of the western ghats on the current climate pattern of peninsular India

The 1500-km-long Western Ghats mountain barrier of peninsular India interacts with the southwest monsoon in a manner which bears heavily on the exceptionally varied climate pattern of the Deccan. Karnataka Province alone concentrates five of the six major climate types of the entire Indian Union. This review explores the interactions between atmospheric structure over South Asia and relief and discusses the efficiency with which the passive margin uplift, second only to the Himalayan barrier, acts as a climatic gatekeeper to the subcontinent. Particular attention is given to rainfall patterns and regimes. These are revealed by a variety of statistical classification and mapping techniques, and the analysis is guided by the steep environmental gradient observed on the immediate backslope of the Ghats, where annual totals can drop from 6000 to 600 mm in ca. 80 km. This is strongly reflected in the landform, soil, vegetation and cropping patterns and raises the question of the relationship between the uplift history of the mountain barrier at geological time-scales, the history of the South Asian monsoon circulation and the stability and diversity of the climatic pattern as seen today. The tightly arranged suite of bioclimatic regions also provides a unique geographical backdrop to the agricultural diversity of South India, rarely found on such a scale in other monsoon contexts of the Tropics.