TR-45 : Distribution of precipitation with elevation

Abstract

Precipitation is known to vary largely in space and time due to several factors such as topography, nature of weather system, geography, aerosol content and drop size distribution in cloud etc. Precipitation is generally believed to increase with elevation. Further, the variation of precipitation with elevation is affected by wind fluctuation, orientation of the hill slope with respect to wind flow. The effect of altitude on precipitation on windward slopes was observed to increase exponentially.

In India, systematic and scientific studies on variation of precipitation with elevation are limited mainly because of lack of sufficient information on the amount of precipitation at higher elevation. This is due to non-availability of automated recording precipitation gauges and problems associated with measurement of precipitation at such higher elevation on a routine basis. In this Technical Note studies on the influence of orography on precipitation and its variation with elevation are reviewed with particular emphasis on the nature of precipitation distribution in Indian mountainous regions.

The review indicated that rainfall in the mountainous areas of western Ghats is more as compared to the precipitation at corresponding elevation in the Himalayas. The precipitation increases with elevation up to a certain level and decreases thereafter. The level of maximum varies from place to place depending on local topography. The period of maximum precipitation at higher altitudes is generally earlier than at foot hills.

Information on the variation of precipitation with elevation would be useful in determining the net increase in precipitation due to elevation, thereby helping in the estimation of PMP for mountainous catchments.