scholarly journals Rainfall Variability over Mountainous and Adjacent Lake Areas: The Case of Lake Tana Basin at the Source of the Blue Nile River

2009 ◽  
Vol 48 (8) ◽  
pp. 1696-1717 ◽  
Author(s):  
Alemseged T. Haile ◽  
Tom Rientjes ◽  
Ambro Gieske ◽  
Mekonnen Gebremichael
Keyword(s):  
Rainfall Variability ◽  
Temporal Patterns ◽  
Time Variability ◽  
Nile River ◽  
Mountainous Area ◽  
Spatial And Temporal Patterns ◽  
Lake Tana ◽  
Blue Nile ◽  
Spatial Correlation Structure ◽  
Hourly Rainfall

Abstract The water resource of the Blue Nile River is of key regional importance to the northeastern African countries. However, little is known about the characteristics of the rainfall in the basin. In this paper, the authors presented the space–time variability of the rainfall in the vicinity of Lake Tana, which is the source of the Blue Nile River. The analysis was based on hourly rainfall data from a network of newly installed rain gauges, and cloud temperature indices from the Meteosat Second Generation (MSG–2) Spinning Enhanced Visible and Infrared Imager (SEVIRI) satellite sensor. The spatial and temporal patterns of rainfall were examined using not only statistical techniques such as exceedance probabilities, spatial correlation structure, harmonic analysis, and fractal analysis but also marginal statistics such as mean and standard deviation. In addition, a convective index was calculated from remote sensing images to infer the spatial and temporal patterns of rainfall. Heavy rainfall is frequent at stations that are relatively close to the lake. The correlation distances for the hourly and the daily rainfall are found at about 8 and 18 km, respectively. The rainfall shows a strong spatially varying diurnal cycle. The nocturnal rainfall was found to be higher over the southern shore of Lake Tana than over the mountainous area farther to the south. The maximum convection occurs between 1600 and 1700 local standard time (LST) over the Gilgel Abbay, Ribb, and Gumara catchments, and between 2200 and 2300 LST over Lake Tana and the Megech catchments. In addition, the hourly rainfall of the station with the highest elevation is relatively closely clustered as compared to those stations at lower elevation. The study provides relevant information for understanding rainfall variation with elevation and distance from a lake. This understanding benefits climate and hydrological studies, water resources management, and energy development in the region.

scholarly journals Rain event properties at the source of the Blue Nile River

2011 ◽  
Vol 15 (3) ◽  
pp. 1023-1034 ◽  
Author(s):  
A. T. Haile ◽  
T. H. M. Rientjes ◽  
E. Habib ◽  
V. Jetten ◽  
M. Gebremichael
Keyword(s):  
Rain Rate ◽  
Rainfall Data ◽  
Nile River ◽  
Rain Event ◽  
Spatial And Temporal Patterns ◽  
Mountain Area ◽  
Event Duration ◽  
Blue Nile ◽  
Event Time ◽  
Rain Events

Abstract. In the present study, spatial and temporal patterns of rain event properties are analysed. These event properties are rain event depth, event duration, mean event rain rate, peak rain rate and the time span between two consecutive rain events which is referred to as inter-event time (IET). In addition, we assessed how rain event properties change when the period over which rainfall data is aggregated changes from 1 to 6 min and when the minimum inter-event time (MIT) changes from 30 min to 8 h. Rainfall data is obtained from a field campaign in two wet seasons of June–August (JJA) of 2007 and 2008 in Gilgel Abbay watershed that is situated at the source basin of the Upper Blue Nile River in Ethiopia. The rainfall data was automatically recorded at eight stations. The results revealed that rain event depth is more related to peak rain rate than to event duration. At the start and towards the end of the wet season, the rain events have larger depth with longer duration and longer IET than those in mid-season. Event rain rate and IET are strongly related to terrain elevation. Sekela which is on a mountain area has the shortest IET while Bahir Dar which is at the south shore of Lake Tana has the longest IET. The period over which rainfall data is aggregated significantly affected the values of rain event properties that are estimated using relatively small value (30 min) of MIT but its effect diminished when the MIT is increased to 8 h. It is shown that increasing the value of MIT has the largest effect on rain event properties of mountain stations that are characterised by high rainfall intermittency.

Evaluation of satellite rainfall estimates over the Lake Tana basin at the source region of the Blue Nile River

2018 ◽  
Vol 212 ◽  
pp. 43-53 ◽  
Author(s):  
Ayele Almaw Fenta ◽  
Hiroshi Yasuda ◽  
Katsuyuki Shimizu ◽  
Yasuomi Ibaraki ◽  
Nigussie Haregeweyn ◽  
...  
Keyword(s):  
Source Region ◽  
Nile River ◽  
Lake Tana ◽  
Blue Nile ◽  
Satellite Rainfall ◽  
Rainfall Estimates ◽  
Lake Tana Basin

scholarly journals Rain event properties and dimensionless rain event hyetographs at the source of the Blue Nile River

2010 ◽  
Vol 7 (4) ◽  
pp. 5805-5849 ◽  
Author(s):  
A. T. Haile ◽  
T. Rientjes ◽  
E. Habib ◽  
V. Jetten
Keyword(s):  
Rainfall Data ◽  
Nile River ◽  
Rain Event ◽  
Spatial And Temporal Patterns ◽  
Wet Season ◽  
Mountain Area ◽  
Event Duration ◽  
Blue Nile ◽  
Peak Intensity ◽  
Rain Events

Abstract. In the present study, the spatial and temporal patterns of the rain event properties are analysed. The event properties are rain event depth, event duration, mean event intensity, peak intensity and the time span between two consecutive rain events which is referred to as inter-event time (IET). Dimensionless event hyetographs are established by relating fractions of event intensities to the corresponding fractions of event durations. The spatial variation of the characteristics of the hyetographs is also evaluated. A model in the form of the beta distribution function is applied to reproduce the dimensionless hyetographs. Rainfall data is obtained from a field campaign in two wet seasons of June–August (JJA) of 2007 and 2008 in the Gilgel Abbay watershed that is situated at the source basin of the upper Blue Nile River in Ethiopia. The rainfall data was recorded at eight stations. The results reveal that rain event depth is more related to peak intensity than to event duration. At the start and towards the end of the wet season, the rain events have larger depth with longer duration and longer IET than the rain events in the mid-season. Mean event intensity and IET are strongly related to terrain elevation. Sekela which is on a mountain area has the shortest IET while Bahir Dar which is at the south shore of the lake has the longest IET.

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