African Journals Online
SINET: Ethiopian Journal of Science

Vol. 23, No. 2 (December 2000)

SOME ASPECTS OF CLIMATE VARIABILITY IN THE NORTH EAST ETHIOPIAN HIGHLANDS - WOLLO AND TIGRAY

D. Conway

School of Development Studies, University of East Anglia
Norwich NR4 7TJ, UK


ABSTRACT: This paper presents a review of climate variability in the northeast Ethiopian Highlands, particularly Wollo and Tigray, during the last 10000 years (the Holocene) and an analysis of rainfall variability during the historical period. To date little work has been done on climate reconstruction in Tigray and Wollo, however, a number of ongoing studies in the area using palaeosoil analysis, archaeological techniques and lake level reconstruction will help reveal the magnitude of past climate variability in the region. On recent time scales, rainfall over Wollo is characterised by a distinctive bi-modal pattern with Belg rains in April-May preceding the main wet season Krempt, July to September, which is typical of the study region along much of the eastern escarpment. Further north over Tigray the Belg rains are less marked and the main Krempt rains dominate the seasonal pattern. Only three stations in the region, Dessie, Combolcha and Mekele, possess relatively unbroken records back to the 1950s. In all three, 1984 stands out as the driest year on record due to very low rainfall during the Krempt season, whilst 1999's Belg season was the driest on record. Although the succession of dry years between the late 1970s and late 1980s produced the driest decade in the Ethiopian Highlands this century there is no evidence for a long-term trend or change in the region's annual rainfall regime. Rainfall during the 1990s has seen a return to more humid conditions since the dry 1980s. The paper ends with a discussion of the major influences on rainfall variability over the Ethiopian Highlands: the El Niño-Southern Oscillation - El Niño events tend to be associated with lower than average rainfall; Atlantic, Indian and Pacific Ocean sea surface temperatures play a varying role in different seasons; the strength of the Indian Summer Monsoon; and the frequency of several tropical depressions over the Southwest Indian Ocean. 

Key words/phrases: Climate, El Niño, Ethiopian Highlands, Holocene, rainfall variability 

TWO JACKKNIFE ESTIMATORS FOR THE SIGNAL 
AND COMPARISON OF THEIR PERFORMANCE 
BY A MONTE CARLO SIMULATION

Temesgen Zewotir 1 and Eshetu Wencheko 2,

1 Department of Statistics and Demography
National University of Lesotho, Roma, Lesotho

2 Department of Statistics, Faculty of Science
Addis Ababa University, PO Box 1176, Addis Ababa, Ethiopia


ABSTRACT: The paper introduces two jackknife estimators of the signal. The mean square errors of the proposed estimators and two other estimators of the signal are studied by simulation. The results of the study show that in designs having weak to mild collinearities both jackknife estimators are more efficient than the naive estimator as well as non-negative minimum biased estimator. The non-negative minimum biased estimator performs better under strong collinearity.

Key words/phrases: Jackknife estimators, mean square error, non negative minimum biased estimator, naive estimator, pseudo-values


CONSISTENCY OF s2 IN THE LINEAR REGRESSION MODEL WHEN THE DISTURBANCES ARE SPATIALLY CORRELATED

Butte Gotu

Department of Statistics, Faculty of Science, Addis Ababa University
PO Box 1176, Addis Ababa, Ethiopia


ABSTRACT: Conditions for the consistency of the estimator S 2 of the variance of the disturbance 1 under first?order spatial error processes are given.

Key words/ phrases: Consistency, ordinary least squares estimator, spatial correlation, spatial error process

WATER POLLUTION BY NATURAL INORGANIC CHEMICALS IN
THE CENTRAL PART OF THE MAIN ETHIOPIAN RIFT

Tamiru Alemayehu

Dept of Geology and Geophysics, Faculty of Science
Addis Ababa University, PO Box 1176, Addis Ababa, Ethiopia


ABSTRACT: The natural surface water and shallow groundwater quality in the Ethiopian Rift is influenced by excessive input of fluoride and some inorganic chemical constituents such as Li, Sr, Pb, Cu and Hg from the deep groundwater system. The surface water bodies are characterised by high fluoride, bicarbonate and chloride concentration far above the recommended consumption limit. The quality of surface water in the Ethiopian Rift is influenced by the complex geological activities, which increase the concentration of undesirable chemical constituents in surface waters by transfer from deep groundwater in the form of thermal springs, geysers and fumaroles. In fact, the concentration of some of the aforementioned chemical constituents highly exceeds the consumption limits giving rise to serious health problems to the local population. 

Key words/phrases: Deep groundwater, inorganic chemical pollutants, Main Ethiopian Rift, teeth mottling, thermal springs

BIRD STRIKE INCIDENCE AT ADDIS ABABA 
BOLE INTERNATIONAL AIRPORT

Elizabeth Yohannes, Afework Bekele and Zerihun Woldu

Department of Biology, Faculty of Science, Addis Ababa University
PO Box 1176, Addis Ababa, Ethiopia


ABSTRACT: The time and rate of bird strike incidences, species composition and number of birds involved in strikes, and the behaviour of birds were recorded at Bole International Airport from December 1994 to December 1995. The gut contents of the birds struck by aircraft were analyzed. A total of 33 bird strikes were recorded during the study period. Fifteen species of birds were involved in the strikes. Pigeons (Speckled pigeons, White-collard pigeons and Red eyed doves together), Black kites and Eurasian bee-eaters were responsible for 33, 24 and 18% of all the strikes recorded, respectively. Most bird strikes took place between September and October while the number of bird strikes between May and June were the least. Most of the bird strikes occurred in the early mornings when most flights leave or arrive. In 69% of the gut analysis carried out, the stomachs or crops were found empty mainly because strikes occurred in early mornings before the birds had fed. The bird strike prevention measures suggested include biological and physical methods.

Key words/phrases: Airport, behaviour, bird strike, Bole

REPRODUCTIVE BIOLOGY AND FEEDING HABITS
OF THE CATFISH CLARIAS GARIEPINUS (BURCHELL)
(PISCES: CLARIIDAE) IN LAKE AWASSA, ETHIOPIA

Elias Dadebo

Department of Animal Production and Rangeland Management
Awassa College of Agriculture, PO Box 5, Awassa, Ethiopia


ABSTRACT: Breeding and feeding habits of the catfish Clarias gariepinus, in Lake Awassa Ethiopia, were studied from samples collected between February 1987 and March 1988. Breeding started at the beginning of the early rains in February and continued until June, after which the proportion of breeding females declined gradually while the proportion of breeding males declined sharply. The sex ratio was not significantly different from unity, because 50.4% females and 49.6% males were caught during the investigation. The smallest ripe female in the catch was 34.0 cm total length (TL) and the smallest ripe male caught was 33.0 cm TL. The weight of ripe ovaries ranged from 11.2 to 962.0 g and the number of eggs ranged from 8,800 to 650,000 eggs. The number of wet weight of preserved eggs per gram ranged from 435 to 1176 with a mean of 669. C. gariepinus was found to be carnivorous in its feeding habit and fish was the most important food item. It contributed 81.7% of the food items of the juveniles and 86.8% of the food of the adults by volume. A cichlid fish (Oreochromis niloticus) was the most utilized prey of C. gariepinus. O. niloticus accounted for 71.0% of the food eaten by juvenile fish (16.3B35.0 cm TL) and 77.5% of the food of adults by volume. Other food items found in the stomachs of C. gariepinus include insects, fish eggs, gastropods, pieces of macrophytes, detritus and zooplankton.

Key words/phrases: Clarias gariepinus, food, Lake Awassa, piscivory, reproduction

EFFECT OF AZOSPIRILLUM ISOLATES ON THE 
GROWTH AND NITROGEN CONTENT OF TEF
[ERAGROSTIS TEF (ZUCC.) TROTTER]

Solomon Zewdie 2, Fassil Assefa 1, and Masresha Fetene 1

1 Department of Biology, Faculty of Science, Addis Ababa University
PO BOX 1176, Addis Ababa Ethiopia

2 Wondo Genet Forestry College, Wondo Genet, Ethiopia


ABSTRACT: Two dizotrophi bacteria, coded as A31 and A32, were isolated from the rhizosphere of two tef varieties DZB01B354 and DZB01-196, respectively. Different morphological, biochemical, and physiological comparisons with type cultures Azospirillum lipoferum, ATCC 29707, and Azospirillum brasiliense, ATCC 29145 showed that the isolates belong to A. lipoferum. Inoculation studies of isolates on pot-grown tef plants showed marked increases in height, grain yield, total shoot and root weight, root-shoot ratio and total grain nitrogen. An increase in grain yield up to 12% over uninoculated controls was observed. The bacterial isolate A32 was found to perform better than A31 in promoting growth and yield on both homologous and heterologous tef varieties. Of the two tef varieties, DZB01B096 responded better than DZB01B354 to inoculation. The study indicats a possible specific interaction between host cultivar and bacterial isolate that governs plant yield. 

Key words/phrases: Azospirillum lipoferum, yield increase, Eragrostis tef


ENHANCING THE POTENCY OF VEGETABLE OILS BY 
COMBINING WITH PIRIMIPHOS-METHYL FOR PROTECTION OF STORED COWPEA AGAINST INFESTATION BY
CALLOSOBRUCHUS MACULATUS (FAB.)

D. Obeng-Ofori and S. Amiteye

Department of Crop Science, University of Ghana
PO Box 44 Legon, Ghana


ABSTRACT: The cowpea beetle Callosobruchus maculatus (Fab.) is a major insect pest of stored cowpea in Ghana. The efficacy of coconut, groundnut and soybean oils applied at 1, 2, 5 and 10 ml kg-1 and pirimiphos-methyl at 2.5, 5.0 and 10 ml active ingredient in 2 ml of water kg-1 of grain (1/16, 1/8 and 1/4 of the recommended dose) alone or in combination to adults and immature stages of C. maculatus and the persistence of the treatments in cowpea grain were evaluated in the laboratory. All the treatments caused significant mortality compared to untreated controls. Lower dosages of the oils and pirimiphos-methyl when combined were highly toxic to C. maculatus. The mixtures also completely inhibited the development of immature stages of the beetle. Only pirimiphos-methyl and the mixtures remained effective 60 days after application. Pirimiphos-methyl can be used at reduced rates if combined with lower dosages of vegetable oils to control the infestation of C. maculatus in stored cowpea. 

Key words/phrases: Callosobruchus maculatus, cowpea, mortality, pirimiphos-methyl, potency

Review article

FREE-LIVING LIMNIC NEMAFAUNA OF ETHIOPIA: A REVIEW OF THE SPECIES REPORTED OUTSIDE THE RIFT VALLEY

Eyualem Abebe 

Department of Biology, Bahir Dar University
PO Box 223 Bahir Dar, Ethiopia

ABSTRACT: The available information on free-living limnic nematodes from Ethiopia is reviewed with special emphasis on those reported outside the Rift Valley, for which species are listed with their corresponding sites of occurrence. The families Monhysteridae, Dorylaimidae, and Tobrilidae comprise more than half of the total of 91 species hitherto reported from Ethiopia. Among 69 species reported outside the Rift Valley, a similar trend of dominance is observed. Of these, about a quarter of the species have never been reported out of their corresponding type localities (in Ethiopia). Most of the remaining are either cosmopolitan or have been reported earlier from Africa. The occurrence of the fifteen most widely distributed species is shown on maps. Brevitobrilus graciloides is the most widely distributed species. Studies on abundance and diversity, though limited, are also included.

Key words/phrases: Aquatic nematofauna, free-living nematodes, inland water bodies