Victor Ongoma

Estimation of mean monthly global solar radiation using sunshine hours for Nairobi City, Kenya

This study estimates the total solar radiation potential over Nairobi City. Several theoretical models based on the initial work of Angstrom have been used to estimate the global solar radiations on a horizontal surface for the city, using bright sunshine hours for the period 2004–2014. The models were developed using the 2004–2012 sunshine hours data and validated by comparing with measured values for 2013 and 2014. Dependencies of the models were tested using Mean Bias Error, Root Mean Square Error, the Nash–Sutcliffe Equation and t-statistics. The result of clearness index for Nairobi shows that the sky is clear all year round except during the June-July-August season where KT is less than 0.5. Most models tested in the current studies were able to adequately estimate daily mean monthly global radiation from sunshine duration with Akinoglu and Ecevit model giving the best estimation.

Diagnosis of the 2010 DJF flood over Zambia

This study diagnoses the circulation anomalies associated with the 2010 December–February (DJF) flood in comparison with the 1992 DJF drought over Zambia. Monthly precipitation data for 39 meteorological stations were sourced from Zambia Meteorological Department, the Climate Research Unit precipitation data, and reanalysis datasets are used. Composite analysis was employed to understand the circulation anomalies during the period under review. Results show that the average precipitation over Zambia was above normal; however, some parts of the country received normal rainfall. The climatology of zonal wind is characterized by easterly flow except at low level. During the flood year, this flow was enhanced as observed in the anomalous vertical cross section of the zonal wind; a reversed flow was observed during the drought year. The region was characterized by rising motion during the flood year, which is associated with convergence at low level and divergence at upper level, as opposed to the drought year which exhibited sinking motion. Convergence at low level leads to vertical stretching, whereas divergence at low level leads to vertical shrinking, which suppresses convection due to subsidence. The observed atmospheric circulations can be monitored in the update of seasonal weather forecast to avert the losses associated with floods in future.

Geomorphological and Land Use Mapping : A Case Study of Ishwardi Under Pabna District , Bangladesh

The study presents geomorphological and land use mapping of the north western part of Ishwardi Upazila under Pabna district, Bangladesh. The objective of the research was to identify geomorphologicalunits and to prepare geomorphological and land use mapping based on remote sensing data and extensive field work. The satellite images of SPOT (Band 4) and Landsat TM-2012 were used for interpretation of geomorphological units. Land use elements are mapped using SPOT satellite images (Band 4) incorporated with field observation data.The study area consists of active channels, abandon channels, natural levees, flood plains, flood basins and lateral channel bars. The results revealed the need for regional and local land use policy revision employing a multi-disciplinary approach for sustainable development. The study advocates for the integration of geological factor in initial for land use planning in order to avoid damage of property and loss of lives. However, the study calls for further research work using different and longer data sets.

Observed surface ozone trend in the year 2012 over Nairobi, Kenya

Clean air is a basic requirement for human health and wellbeing. The Kenya Meteorological Department has established air pollution monitoring activities in various sites in Nairobi, at Dagoretti Corner meteorological station and at Mount Kenya. Different pollutants are measured including ozone. The increased concentration of greenhouse gases in the atmosphere has influenced the weather and climate. This study examined the variations of surface ozone over Dagoretti Corner, Nairobi for a 12-month period ending July 2013, exactly one year after the start of data acquisition. The trend was studied using time series analysis of ozone concentration on both an hourly and monthly basis. The ozone data was then combined with meteorological data and temperature to find correlations between the two. Overall, the air quality of Nairobi, represented by Dagoretti Corner meteorological station is good as compared to the World Meteorological Organization ozone standards. The highest concentration of ozone is observed in the afternoon and the minimum at dawn on a daily basis. On seasonal scale, the highest levels are recorded in the cold months. This information helps to reduce exposure to the gas and thus to reduce its impacts on living things. The study recommends the reduction of exposure to the gas during the times when it has been observed to be highest in order to minimize its impacts.

Evaluation of CMIP5 twentieth century rainfall simulation over the equatorial East Africa

This study assesses the performance of 22 Coupled Model Intercomparison Project Phase 5 (CMIP5) historical simulations of rainfall over East Africa (EA) against reanalyzed datasets during 1951–2005. The datasets were sourced from Global Precipitation Climatology Centre (GPCC) and Climate Research Unit (CRU). The metrics used to rank CMIP5 Global Circulation Models (GCMs) based on their performance in reproducing the observed rainfall include correlation coefficient, standard deviation, bias, percentage bias, root mean square error, and trend. Performances of individual models vary widely. The overall performance of the models over EA is generally low. The models reproduce the observed bimodal rainfall over EA. However, majority of them overestimate and underestimate the October–December (OND) and March–May (MAM) rainfall, respectively. The monthly (inter-annual) correlation between model and reanalyzed is high (low). More than a third of the models show a positive bias of the annual rainfall. High standard deviation in rainfall is recorded in the Lake Victoria Basin, central Kenya, and eastern Tanzania. A number of models reproduce the spatial standard deviation of rainfall during MAM season as compared to OND. The top eight models that produce rainfall over EA relatively well are as follows: CanESM2, CESM1-CAM5, CMCC-CESM, CNRM-CM5, CSIRO-Mk3-6-0, EC-EARTH, INMCM4, and MICROC5. Although these results form a fairly good basis for selection of GCMs for carrying out climate projections and downscaling over EA, it is evident that there is still need for critical improvement in rainfall-related processes in the models assessed. Therefore, climate users are advised to use the projections of rainfall from CMIP5 models over EA cautiously when making decisions on adaptation to or mitigation of climate change.

Trends in Extreme Climate Events over Three Agroecological Zones of Southern Ethiopia

The study aims to assess trends in extremes of surface temperature and precipitation through the application of the World Meteorological Organization’s (WMO) Expert Team on Climate Change Detection and Indices (ETCCDI) on datasets representing three agroecological zones in Southern Ethiopia. The indices are applied to daily temperature and precipitation data. Nonparametric Sen’s slope estimator and Mann–Kendall’s trend tests are used to detect the magnitude and statistical significance of changes in extreme climate, respectively. All agroecological zones (AEZs) have experienced both positive and negative trends of change in temperature extremes. Over three decades, warmest days, warmest nights, and coldest nights have shown significantly increasing trends except in the midland AEZ where warmest days decreased by 0.017°C/year ( ). Temperature extreme’s magnitude of change is higher in the highland AEZ and lower in the midland AEZ. The trend in the daily temperature range shows statistically significant decrease across AEZs ( ). A decreasing trend in the cold spell duration indicator was observed in all AEZs, and the magnitude of change is 0.667 days/year in lowland ( ), 2.259 days/year in midland, and 1 day/year in highland ( ). On the contrary, the number of very wet days revealed a positive trend both in the midland and highland AEZs ( ). Overall, it is observed that warm extremes are increasing while cold extremes are decreasing, suggesting considerable changes in the AEZs.

Regional Features and Seasonality of Land–Atmosphere Coupling over Eastern China

Land–atmosphere coupling is a key process of the climate system, and various coupling mechanisms have been proposed before based on observational and numerical analyses. The impact of soil moisture (SM) on evapotranspiration (ET) and further surface temperature (ST) is an important aspect of such coupling. Using ERA-Interim data and CLM4.0 offline simulation results, this study further explores the relationships between SM/ST and ET to better understand the complex nature of the land–atmosphere coupling (i.e., spatial and seasonal variations) in eastern China, a typical monsoon area. It is found that two diagnostics of land–atmosphere coupling (i.e., SM–ET correlation and ST–ET correlation) are highly dependent on the climatology of SM and ST. By combining the SM–ET and ST–ET relationships, two “hot spots” of land–atmosphere coupling over eastern China are identified: Southwest China and North China. In Southwest China, ST is relatively high throughout the year, but SM is lowest in spring, resulting in a strong coupling in spring. However, in North China, SM is relatively low throughout the year, but ST is highest in summer, which leads to the strongest coupling in summer. Our results emphasize the dependence of land–atmosphere coupling on the seasonal evolution of climatic conditions and have implications for future studies related to land surface feedbacks.摘 要陆-气耦合是气候系统中的重要过程, 已经有大量基于观测和数值模拟的研究提出了各种耦合机制. 土壤湿度影响蒸散发进而引起地表温度异常是陆-气耦合研究中的重要组成部分. 利用ERA-Interim再分析资料和CLM4.0模拟结果, 本研究进一步探讨了土壤湿度/地表温度与蒸散发之间的关系, 以更好地理解中国东部地区陆-气耦合的复杂性质(即空间和季节变化). 本研究发现陆-气耦合的两个诊断量(即土壤湿度与蒸散发的相关系数和地表温度与蒸散发的相关系数)的变化主要依赖土壤湿度和地表温度的气候状态, 存在明显的空间变化和季节演变. 结合两个相关系数, 本研究确定了中国东部的两个陆-气耦合的关键区: 西南和华北地区. 在西南地区, 土壤湿润, 温度较高, 但在旱季的时候土壤湿度显著下降, 春季达到最低, 因此春季表现为较强的陆气耦合. 而在华北地区, 土壤湿度在年内维持在较低的水平, 仅在较为温暖的季节才有足够的能量将土壤中的水分蒸发至大气, 因此陆-气耦合强度随着温度的季节变化而发生改变, 夏季最强. 本文的研究结果强调了陆-气耦合对气候条件季节演变的依赖性, 为未来有关陆面过程反馈的研究提供一定的参考.

Socio-Economic and Environmental Analysis of Wind Power Projects as Viable Renewable Energy Resources in Kenya

The demand for power in Kenya is on the increase with the ongoing growth of the country’s economy. There is a need for the country to balance energy efficiency, sustainability and low-carbon technologies. This entails drafting and implementing policies and strategies towards a low-carbon development path, ranging from fuels, technologies and infrastructure. This work examines the drivers of renewable energy resources in Kenya, focusing on Ngong Wind Farm. Results show that most low-carbon innovations in Kenya are driven by government tariffs and policies. Funding, and political and community goodwill remarkably influence the success of wind power projects in Kenya. The case study is a novel experiment that offers sustainable alternatives in the energy sector. There is need for more investment in the renewable sector, especially in the set up of power plants and power storage. To address the shortcomings in the renewable energy sector, there is a need for further research and development, and collaborations to foster innovations in the wind power sector in country. A combination of knowledge and resources, and leveraging local and national policies are potential ways in which institutional platforms can foster wind technology advancement and dissemination.

Relationship between the North Atlantic Oscillation Index and October-December Rainfall Variability Over Kenya

Rainfall performance and variability are the major problems that affect many socio-economic activities in Kenya. This study investigates the relationship between the North Atlantic Ocean Oscillation (NAO) Index and October – December (OND) rainfall variability over Kenya. Rainfall, wind, geopotential height, temperature, moiture transport and NAO Index (NAOI) values for the period 1961 - 2010 are investigated. The region experiences rainfall that is highly variable in space and time; with the country generally experiencing bimodal rainfall. There is an insignificant negative correlation between the OND rainfall and NAOI over most parts of the country except for the Lake Victoria region that experiences significant correlation at 90% significance level. The study recommends further research on how the NAOI can be used as a predictor for OND seasonal rainfall over the lake region.

A Review and Assessment of Applicability of the Heat Stress Indices in Kenyan Weather Forecast

The weather and climate of any given place is an environmental resource, it greatly determines the socio-economic and political life of humans and other living things. The packaging of weather information especially the forecast into a way that can easily be interpreted and understood by end users is of very important. Temperature is one of the weather parameters that have significant impact of human comfort and the wellbeing of other living things. Thermal stress is an important factor in many industrial situations, games and military operations among others. It therefore calls for accurate and timely forecast of the same and dissemination to the public for human safety and comfort. There exist three types of heat strain indices: rational, empirical and direct indices. The study tested the applicability of Discomfort Index (DI) in Kenyan daily weather forecast using both observed and forecast data from Consortium for Small-Scale Modelling (COSMO) model used by Kenya Meteorological Department (KMD). The discomfort index (DI) forecasted by the Small-Scale Modelling (COSMO) model gives a relatively good representation of the observed and the study thus recommends that KMD adopt it in its forecast.