Application of Water Balance concepts for a Climatic Study Of Droughts in South India

Abstract

Droughts in India are widely known to be caused by failures of monsoon-the main source of rainfall. These droughts are usually at the root of many famines and, therefore, they constitute an important study in applied climatology.

As droughts are not mere shortages of rainfall, they can never be defined without reference to area moisture available in the soil; they are today regarded to be such periods of dryness that affect the growth and development of vegetation.

Of the several methods of drought study, the water balance method which compares the water supply of a region by precipitation with water need or potential evapotranspiration has gained wide usage due to its versatility and has been successfully used by Palmer in the United States of America. Hence this method was employed for this analytical study of droughts in this paper.

Initially, a standard map of climatic types of India prepared by Subrahmanya. In according to the 1955 scheme of Thornthwaite was taken and three representative stations-Bijapm (Arid), Trichy (Semi-arid) and Cuddalore (Drysub-humid)-were selected from the dry climatic zones of south India. Yearly aridity indices for each station were evaluated for a period of 65 years (1891-1955) and their time-trends along with the 7-yearoverlapping means were graphed and presented. Drought years were picked from these diagrams and their water balances discussed in relation to the climatic situations normal to the stations.