ASSESSMENT OF TEMPORAL VARIABILITY OF RAINFALL AND  IDENTIFICATION OF PARENT DISTRIBUTION IN DIRE DAWA,  EASTERN ETHIOPIA
Creators: name: MOHAMMED HOSH ADEN
Publisher: name: National Academic Digital Repository of Ethiopia
Year: 2015

description: Rain variability in space and time is one of the most relevant characteristics of tropical rain forest 
that is associated with economic, social and ecological implications. Extreme rain events have 
significant environmental consequences that cause considerable damages in urban as well as in 
rural areas. Temporal variability of  precipitation is a key factor influencing the structure and 
function of semiarid ecosystems. The climate of the Dire Dawa Administration is being located 
in an arid and semi-arid part of  the country and dominated by various inter-related factors, 
altitude being the most determinant factor and the temporal variability of precipitation affects 
the runoff process. This resulted in  flash flood disasters and drought during recent years and 
requires  an  urgent  course  of  mitigation  measures  to  alleviate  the  associated  problems.  This 
requires detail information regarding the temporal distribution of annual, seasonal  and monthly
rainfall pattern in the region. The present study has been carried out for 20 different probability 
distribution {gamma (2P, 3P), generalized gamma (3P, 4P), logistic, log-logistic (2p, 3p), log
gamma, normal, lognormal (2P, 3P), Weibull (2P, 3P), Pearson 5 (2P, 3P), pearson 6 (3P, 4P), 
log-pearson 3, generalized extreme value and Gumbel’s maximum  distribution } and  associated 
goodness  of  fit  test   using  Kolmogorov   Smirnov,  Anderson  Darling   and  Chi-Squared  tests. 
Temporal rainfall variability is assessed using statistical trend  analysis  of the monthly, seasonal 
and annual rainfall using the Mann–Kendall test, the Sen’s slope estimator and spearman’s Rho 
test. It was observed that according to Kolmogorov Smirnov and Anderson Darling test, 
Generalized Extreme value  distribution fits well to the rainfall data  occupying 45% and 40% 
respectively and the log logistic (3p) obtained 32% according to Anderson Darling. Among these 
distributions 41% of the rainfall follows general extreme value while 24% and 18% of the Dire 
Dawa Administration rainfall gamma (2p) and log logistic (3p) distribution respectively. The best 
distribution  for  one  day  maximum  rainfall  received  during  different  months  in  a  39  year  was 
Generalized Extreme Value and it can be seen that April month  received the highest amount of 
one day maximum rainfall (25%) followed by January, March and August with the same percent 
of (13%). The minimum rainfall of 27.4 mm rainfall can be expected to occur with 97.5 per cent 
probability and one year return period and a maximum of 137.5 mm rainfall can be received with 
one per cent probability and 200 year return period.  There are rising rates of precipitation in some 
months and decreasing trend in some other months obtained by Mann-Kendall Test together with 
the Sen’s Slope and Spearman’s Rho test,  Statistically significant negative were found for both 
Mann-Kendall test and Spearman’s Rho in February at 10% significance level and positive trends 
were  found  in  July  (1%  and  5%  significance  level)  and  November  (5%  significance  level), 
statistically  significant  negative  were  also  found  for  Spearman’s  Rho  test  in  April  at  10% 
significance level. While no significant trends were found for other months.  Therefore it can be 
concluded that there is evidence of some change in the trend of precipitation of the region.