Resolving orographic rainfall on the Indian west coast

Abstract

ABSTRACT:We discuss a method to obtain the spatial estimates of rainfall on the Indian west coast for calculating the surface water budget. The region includes the basin of the Mandovi River, a typical west-coast river whose catchment area includes the Sahyadris range. The rainfall maps obtained by a multivariate interpolation scheme, with elevation as the third variable, were able to capture the sharp increase in rainfall on the windward slopes and the exponential decay in rainfall on the leeward side. The rainfall maps were used to force a hydrological model and the simulated discharge was within 16% of the observed discharge in 16 of 18 years during 1981-1998; the average error over the 18 years was 8%, which is much less than the estimated error of ∼15-20% in the observed discharge. The Mandovi river discharge provided a reliable and independent validation of the accuracy of the rainfall estimate as the river is purely rain-fed. The method provides a better estimate of rainfall in the Mandovi basin, and therefore for the Indian west coast, than existing rainfall datasets. The key result is that treating the windward and leeward sides separately by an a priori, subjective extraction of the ridge line can reduce the underestimation of rainfall that is common in mountainous terrain when the data coverage is sparse.

Performance evaluation of AR4 Climate Models in simulating daily precipitation over the Indian region using skill scores

“…Within the west coast of this zone, a mountain range (Western Ghats) runs parallel to the coast, and the axis of the range lies perpendicular to the prevailing summer-monsoon winds. The moisture-laden monsoon winds cause heavy rainfall on the windward side of the mountains than the rain shadow on the leeward side of the west range (Basu 2005;Suprit and Shankar 2008). The low SSs in the peninsular zones could be due to significant largescale precipitation biases in the models, such as reduced precipitation along the western coast of India and excessive rain over the Indian peninsula observed by Bollasina and Nigam (2009).…”

Large-scale atmospheric forcing and topographic modification of precipitation rates over High Asia – a neural-network-based approach

“…On the local scale, the precipitation distribution over the target area is extremely modified due to the various interactions of moist air masses with complex topography and the accompanying local-scale atmospheric processes (Chen et al, 2014;Guan et al, 2009;Suprit and Shankar, 2008). Many studies show that the elevation plays a crucial role in the distribution of precipitation, although the vertical precipitation gradient in high-mountain regions varies considerably in different target areas.…”

Time-dependence of salinity in monsoonal estuaries

“…The gauge that recorded these data was located near the head of the estuary. With a number of rivers, rivulets, and streams bringing runoff to the Mandovi, it has been estimated that the runoff entering the estuary doubles from head to mouth (Suprit and Shankar, 2008). The runoff is high following an episode of high precipitation over the catchment area of rivers that feed the estuary.…”

“…Runoff at every 2 km from the head to the mouth is calculated using the model results of Suprit and Shankar, (2008). Runoff-induced velocity is then obtained from these runoffs by dividing it by the area of cross-section.…”