Analysis of Rainfall Concentration and Seasonality over a Semi-Arid City (Una) of Gujarat

The Una is in Agro climatic zone VI (South Saurashtra) in Gujarat. The monthly, seasonal, dry and wet seasonal and annual trends for rainfall were analyzed for the period of 1974 to 2017 (44 year). A powerful indicator of the temporal distribution of rainfall is Precipitation Concentration Index (PCI) used for analysis of monthly, seasonal and annual rainfall data. Precipitation Concentration Index is a statistically derived index used in quantifying the relative distribution of the rainfall patterns. Rainfall seasonality is related to the temporal distribution of rainfall on a monthly basis. The normal precipitation near the study area in the basin is highest going up to 2034 mm in 2005 and lowest going up to 239 mm in 1987, with an inter annual variation of 11%. The normal annual rainfall in the study area is 935 mm. About 90%, 50%, 5.2% rainfall is received during the monsoon months of July, August and September respectively. The rainfall analysis over Una (1974 to 2017) implies a decreasing trend in southwest monsoon, while the post and pre monsoon rainfall have increasing trends. This study indicates that the annual rainfall over Una is concentrated roughly in one third of the year or in other words total rainfall occurred in four months and shows strongly irregular rainfall distribution. Citation: Hiran Dhola, Sahita waikhom, V.G. Yadav, Darshan J. Mehta. "Analysis of Rainfall Concentration and Seasonality over a Semi-Arid City (Una) of Gujarat." Global Research and Development Journal For Engineering [ERICE - 2019], Dr. S & S.S. Ghandhy Government Engineering College GTU, (February 2019) : pp. 333 - 337.