Abstract
Rainfall is the most key variable both in atmospheric and hydrological cycle. Its patterns
usually have spatial and temporal variability. This variability affects agricultural
production, water supply, environment, and the existence of its people. Its variability
assumed to be the main cause for the frequently occurring extreme events such as
drought and flood. The main objective of this study is to apply time series techniques to
study the change of monthly rainfall distribution in millimeter in Hawassa city from
January, 2000 to December, 2009 based on the data from Hawassa branch of national
meteorological agency of Ethiopia. The descriptive result showed that, the amount of
rainfall change based on time because there is variation from time to time. The highest
monthly rainfalls were recorded in May 2001, and September 2007. February 2000,
November 2002 and December 2007 recorded the lowest monthly rainfall values. The
implication of this result is that year 2001 and 2007 presented an opportunity for
increased food production and at the same time has the highest risk for flooding and
environmental degradation. The ten years forecasting is done by using ARIMA model. The
forecast result showed that heavy rains will be occurred at an approximate interval of 12
months. On this basis since the last heavy rainfall recorded was in September 2009, it is
expected that the next heavy rainfall value had recorded around July- September, 2010.
The lowest rainfall will be recorded five months in each forecasting years from October-
February. According to this trend, it is observed that the occurrence of dry seasons will be
at each year and mainly in the five months from October-February of the year.
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