Meso-scale distribution of summer monsoon rainfall near the Western Ghats (India)

Abstract

The spatial distribution of southwest monsoon rainfall is studied over Maharashtra State (India), which includes part of the well‐known Western Ghats mountain range, near its western boundary, running almost from north to south, perpendicular to the summer monsoon current in the lower troposphere. Meso‐scale analysis of daily rainfall is performed for Maharashtra State, including the Western Ghats, for the two mid‐monsoon months of July and August, during the 10‐year period of 1971–1980. Strong and weak monsoon days were identified for the 5‐year period of 1976–1980. The meso‐scale pattern of average daily rainfall is obtained separately for strong and for weak monsoon conditions. All these average patterns show the following features: (i) the rainfall increases rapidly from the Arabian Sea coast close to the line of maximum height of the Western Ghats; (ii) there are two rainfall maxima corresponding to the two mountain peaks parallel to the coast line; (iii) between the two mountain peaks, there is a valley which is narrow at the western end (upwind end), broadening towards the east (on the downwind side). Ground contour height of the valley rises eastwards and ends as a part of the Deccan Plateau east of the Ghats. Here the valley opens out like a funnel with higher mountains flanking its two sides. In the valley, the rainfall increases from the coast up to the line of maximum height of the Ghats, and then decreases eastwards towards the plateau. The rainfall isopleths also take a funnel‐shaped configuration. An interesting feature is that near the wider section of the valley funnel, there is a rainfall minimum and then the rainfall increases further eastwards on the downwind side. This feature of rainfall minimum is somewhat similar to the rainfall minimum reported by Asnani and Kinuthia (personal communication); Asnani (Asnani GC. 1993. Tropical Meteorology, Vol. I. Prof. G.C. Asnani: Pune, India; 603) attributed the rainfall minimum to the Bernoulli effect. A somewhat similar phenomenon is assumed in the present study area. Copyright © 2000 Royal Meteorological Society

The weather and climate of the tropics: Part 6 – Monsoons

“…3 Hence, we need a different mechanism to explain the progress of the monsoon than the simple motion of moist southwesterly winds. Indeed the moist flow across India is partially blocked by the Western Ghats, the mountains that mark the west coast of India (Patwardhan and Asnani, 2000). There is copious summer rainfall on the western slopes of these mountains, but the area to their lee remains largely dry, in a rain shadow, the southwesterly air flow having lost some of its humidity.…”

Summer Monsoon Rainfall Variability Over Maharashtra, India

“…Many attempts have been made to identify rainfall zones of the Western Ghats for agriculture planning and management purposes (GADGIL et al 1988;KULKARNI and REDDY, 1994;VENKATESH and JOSE, 2007). The maximum rainfall has been found to occur in the high altitudinal zones (SARKAR, 1967;PATWARDHAN and ASNANI, 2000).…”

“…It is also observed that rainfall activity increases steadily from the coast line to the top of the hills and reduces substantially on the leeward side. The result is in agreement with the work on mesoscale distribution of rainfall over Maharashtra by PATWARDHAN and ASNANI (2000). The leeward side of the mountain receives less rainfall, ranging between 150 and 200 mm, and the minimum rainfall occurs between the latitudes 17°N-18°N and longitudes 74.5°E-75.5°E.…”

Identification of homogeneous rainfall regimes in parts of Western Ghats region of Karnataka

“…It may be noted that most of the studies (Raghavan 1964;Raju 1981;Ramachandran and Banerjee 1983;Gunnell 1997a;Patwardhan and Asnani 2000) have adopted a regional approach in analyzing rainfall variability. However, in the present study, we have adopted a discrete approach to analyse the rainfall regime.…”

“…It is well acknowledged that the Western Ghats enhance rainfall activity substantially under favourable conditions, with increasing trend on the windward and decreasing pattern on the leeward side. The maximum rainfall appears to occur in the high altitudinal zones (Sarkar 1967;Patwardhan and Asnani 2000). Due to such variation in the rainfall pattern, homogeneity in rainfall distribution cannot be expected over the Western Ghat region.…”