ANALYSIS OF SEASONAL RAINFALL VARIABILITY AND DROUGHT PROBABILITY IN SOUTHERN REGION, ETHIOPIA

Abiy Gebremichael (gebremichaelaby@gmail.com)
Agricultural Engineering, Haramaya University
November, 2011
 
he author was born in February 1984 in Bitta Woshi village, Gimbo woreda, at Kafa
zone, SNNPR state Ethiopia.

He started his education at Bitta Woshi Elementary School; senior secondary education at Wushwush and high school education at Bonga compressive secondary school. Upon successful completion of his high school studies, he joined
Mekelle University in September 2001 and graduated with B. Sc. Degree in Land
Resource Management and Environmental Protection (LaRMEP) specializing in Soil and
Water Conservation in the month of July 2005.

Thereafter, he was employed in the Ministry of Agriculture in Kafa zone Agricultural and Natural Resource Bureau, Gimbo wereda where he served for two years as a Soil and Water Conservation Expert.

Then he was employed in Southern Agricultural Research Institute, Bonga Center in December, 2008 as Soil and Water Conservation Researcher where he served until he joined the School of Graduate Studies of Haramaya University in October 2009 academic year.

He is now serving as Soil and Water conservation Researcher at Southern Agricultural Research Institute, Ethiopia.
 

Abstract

ABSTRACT

Agricultural productivity could be adversely affected by high variability of rainfall and its
extreme conditions because it governs the crop yields and determines the choice of the
crops to be grown. Therefore, there is a need to assess the seasonal rainfall variability
and drought probability in selected areas of Southern Nations Nationalities and People
Regional State.

Instat software version 3.36 was used to analyze the onset, end date, the length of growing Period (LGP), and the dry spell lengths variability. Trend test was made by Mann-Kendall, Spearman test and least square regression methods. Homogenous rainfall variability areas were also identified by Principal Component Analysis with
varimax rotation. Similarly, Standard Precipitation and Drought Proneness Indices were used to asses seasonal and dekadal drought respectively. The result shows that, the annual rainfall in the region varied from slightly over 780 mm in Billate station to more than 2110 mm in Gerese station with mean, SD and CV as 1200 mm, 197 mm and 25% respectively. kiremt rainfall varied from 157 mm in Konso to 844 mm in Welkite with mean, SD and CV as 506 mm, 202 mm and 39% respectively. Similarly, the belg seasonal
rain varied from 863 mm in Gerese to 246mm in Bue with mean, SD and CV of 409mm,
121mm and 30% respectively. CV of 15%-64% for kiremt, 17%-52% for belg and 12%-
46% for annual were observed. For Kiremt season, CV greater than 30% was observed in
18 stations; between 20-30% in 10 stations and below 20% for 5 stations. The mean onset,
end and LGP were found to be at April 01, Oct. 06, and 187 days for Hosaina area; April
26, Oct. 16 and 172 days for Welkite area and at March 24, May 25 and 62 days for Gato
area respectively. In addition, two homogenous areas of coherent rainfall variability, in
terms of each belg and kiremt seasons were obtained. The 10 day long dry spell has
probability of occurrence below 40% after March 20 and April 20 in Hosaina and Welkite
respectively so that sowing crops could be shifted accordingly. Similarly, at Gato area, the
probability of dry period of 10 days was below 60% after 1st dekad of March and had
dropped to below 20% in April then progressing to increase to 35% in May. A non
significant decreasing linear trend for 10 stations out of 16 and significant decreasing
trend at Sawla (p<0.05 (-8.15 mm/yr)) and Chida (p< 0.05(-16.08 mm/yr)) were obtained.
6-month SPI showed less seasonal drought probability in Hosaina and Welkite areas.
However, for the start of belg, March was unreliable in two stations while reliable in Gato
area. Therefore, time of planting crops and soil and water conservation activities should
be performed considering this variability.