rainfall analysis by girma mamo

Topics: Statistical significance, Statistical hypothesis testing, Standard deviation Pages: 28 (4211 words) Published: March 29, 2014
Research Paper
Trend and variability of rainfall in Tigray, Northern Ethiopia: Analysis of meteorological data and farmers’ perception
Accepted 11th May, 2013
ABSTRACT

Rainfall is the most important but variable climatic parameter in the semiarid tropics. In this study, the trend and variability of rainfall were compared with the perception of farmers in northern Ethiopia. Daily rainfall data obtained from five meteorological stations located in different agroecological zones were used to determine trends in annual and seasonal totals, onset and cessation dates, length of growing period (LGP) and dry spell length. Sen’s estimator and Mann-Kendall's statistical tests were used for trend detection. Two hundred fifty three farmers from three administrative areas (districts) that are close to the meteorological stations were interviewed in order to investigate farmers' perception on rainfall trend and variability in the study area. The results indicate that rainfall in the region is highly variable with a non-significant trend in both annual and seasonal totals for all stations. However, trends of rainfall events such as onset date, cessation date, LGP, and dry spell length were changed significantly in most stations, which agreed with the farmers’ perception. Moreover, most stations experienced drought conditions in the last decade. The results suggest the need for designing appropriate agronomic and water management strategies to offset the negative impacts of rainfall variability in the study area.

Key words: Rainfall, rainfall trend, rainfall variability, onset, length of growing period.

INTRODUCTION
Agriculture plays a dominant role in the economy of
Ethiopia, contributing 41% GDP, 80% of the employment
and the majority of foreign exchange earnings
(Gebreegziabher et al., 2011). The success of agricultural
production has, therefore, large implications, ranging from
the state of the countrywide economy to the survival of the
subsistence farmers (Block and Rajagopalan, 2007). Natural
rainfall is the main source of water for crop production as
irrigation covers only 5% of the cultivated land in the
country (Awulachew et al., 2010). Several studies (Hagos et
al., 2009; Osman and Sauerborn, 2002) examined the
impact of rainfall variability on the Ethiopian economy, and found that rainfall variability in the country led to a
production deficit (20%) and increase in poverty rates
(25%) which costed the economy over one-third of its
growth potential.

Assessing trends in rainfall characteristics based on past
records together with the perception of the local
community is essential to develop adaptation strategies.
Previous studies dealing with annual and seasonal rainfall
trends in Ethiopia revealed controversial results. Seleshi
and Demaree (1995); Osman and Sauerborn (2002)
indicated high rainfall variability and its negative trend
during the main rainy season (June-September). Using data
in the last half a century, NMSA (2001) reported a
significant reduction in annual rainfall in the north,
southwest part of the country while there was an
increasing trend of annual rainfall in the central part of
Ethiopia. Considering rainfall data of the Amhara Region
(North West Ethiopia), Bewket and Conway (2007)
reported inconsistent results in the annual, kiremt and Belg rainfall trends within the stations of the region. The authors

Academia Journal of Agricultural Research; Hadgu et al.

noted that for the period 1975-2003, kiremt and annual
rainfall shows significantly increasing trend at Dessie and
Lalibela while Debre Tabor revealed significantly
decreasing rainfall trend during both seasons. On the other
hand, Meze-Hausken (2004); Seleshi and Camberlin (2006);
Cheung et al. (2008) did not find any significant trend over the northern and northeastern part of the country.
Previous studies on rainfall analysis concentrated on the
central highlands of the country (Seleshi and...
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