A study on some climatological parameters influencing the physical environment of the Brahmaputra valley

Abstract

Characteristics of climatological parameters such as wind, rainfall and surface air temperature of the Brahmaputra Valley have been studied by using simple statistical methods. Data for varying periods between 1901 and 1980 from 94 stations, in and around the Brahmaputra Valley, have been used in this study. Major emphasis is given to the study of rainfall. The study of wind direction shows that at the lower levels, wind flow pattern in the Brahmaputra Valley is highly affected by the topography of the region and throughout the year, specially at the surface level prevailing direction of the wind is along the downslope of the valley. The surface wind speed has seasonal variation with its maximum value in the month of April. The wind power output is found to be low in all the valley stations of the region. The characteristics of rainfall that are studied and discussed are areal distribution and diurnal, seasonal and annual variations. The results show that spatial and temporal variations of rainfall in the valley are highly complex refle-cting the complex physiography of the region. A diminishing trend of rainfall is also found in many stations of the valley, which is more prominent in north-eastern part. Mean monthly surface air temperature analysis shows four different types of seasonal variation patterns at different locations in the valley. There is a rising trend of daily maximum, minimum and mean temperatures in majority of the stations. Water balance study shows that about 1068.0 litres/m2/yr. surplus rain water in lost as run off during May to September and a deficit of about 97.2 litres/m2/yr. occurs during October to April, causing drought period. Water balance analysis also shows nine types of climates in the valley although the valley as a whole belongs to a climatic type of third humid second mesothermal with negligible winter water deficiency.