Estimation of spatiotemporal variability of precipitation and moisture budget using reanalysis and the ground based data  over upper Blue Nile basin in Ethiopia

Wondie, Megbar

dc.contributor.author	Wondie, Megbar
dc.date.accessioned	2019-12-25T10:06:01Z
dc.date.available	2019-12-25T10:06:01Z
dc.date.issued	2019-12-25
dc.identifier.uri	http://hdl.handle.net/123456789/10093
dc.description.abstract	Upper Blue Nile Basin (UBNB) is the water tower of not only for Ethiopia but also for downstream countries. This region is quite useful for agricultural purposes, owing to essential climate elements such as sufficient precipitation, optimal temperature, surface water (e.g. Lake Tana and Abay basin), and underground water. However, there is no exact mechanism to estimate spatiotemporal precipitation distribution over this region, because UBNB exhibits variable topographic features. Hence to solve this challenge we inferred different precipitation estimation techniques (e.g. weather radar, gauge, satellite, and reanalysis). In Ethiopia, a large study has been conducted on precipitation using rain gauge network data. Gauge precipitation data unable to provide required temporal and spatial distribution over UBNB in Ethiopia because of insufficient network and density of rain gauges. Weather radar provides precipitation with high accuracy and precision through measuring the signal of reflectivity power with large spatial coverage. Moisture budget analysis and recycling ratio was analyzed, because it is an attractive method to determine the relative contribution of the study area moisture for the effect of spatiotemporal precipitation distribution. The precipitation variability was partly derived by the influence of middle and lower atmosphere parameters. This work is focused on the estimation of spatiotemporal variability of precipitation and moisture budget using reanalysis and the ground data over the UBNB in Ethiopia. To this end, we incorporated precipitation, reflectivity, temperature, cloud cover, gravity wave dispersion, outgoing-long wave radiation, incident solar radiation, ozone concentration, carbon dioxide, methane, specific humidity and wind data inferred from 1979-2017. Recently, ground-based (g-b) weather radar was installed at Shawera within UBNB in the northwest of Ethiopia in 2016. Hence, we are interested to develop reflectivity (Z) and rain rate (R) relationship model for the purpose of precipitation estimation after improving the errors. Projectile rainfall motion error correction, the least squared regression, likelihood function, different error metrics, moisture budget equations and Recycling ratio were mostly applied on this study. The derived Z-R relation model parameter values were found to be a multiplicative factor a = 55 and the exponent factor b = 1.12. After applied projectile rainfall motion error correction, a proportional error has been reduced from 0.3 mm to 0.08 mm by 22%. Similarly, random error from -0.08 mm to 0.07 mm by 1% and the total error reduced by 12%. The correlation coefficients between the gauge and the European Centre for Medium-range Weather Forecast (ECMWF) were found 0.82. When we analyzed spatiotemporal distribution of precipitation over the study domain, during summer season most of the UBNB moisture was converted to precipitation around the central parts of the study area, while in spring it contributes to the southern parts of the study area. Furthermore, the northeast part of the study area was affected by the basins` moisture during the autumn season. The calculated recycling ratios for summer, autumn, spring, and winter were 9.70%, 16.33%, 19.01%, and 35.30%, respectively with the annual average value of 20.11%. The salient feature of this thesis is the consideration of the projectile method for improving the radar data over the UBNB in Ethiopia and this method can be suggested to another radar sites in the world. Atmospheric moisture budget analysis reveals that UBNB moisture had a lesser contribution of precipitation over the study area, rather than the neighboring countries. Annual precipitation is directly negatively influenced by temperature, strong gravity waves, and incident solar radiation. Hence, the outcomes from this study will serves as a reference for future configuration and calibration of the radar system in Ethiopia. In order to draw a better conclusion, further studies on moisture budget are required in the context of Ethiopia. Furthermore, consideration of water vapor nuclei on precipitation variability study is very important in addition to the influence of middle atmosphere parameters. Investigation of high gravity wave occurrence frequency is quite useful to predict the severe drought in Ethiopia. _______________________________________________	en_US
dc.subject	physics	en_US
dc.title	Estimation of spatiotemporal variability of precipitation and moisture budget using reanalysis and the ground based data over upper Blue Nile basin in Ethiopia	en_US
dc.type	Thesis	en_US