The Development of a Customization Framework for the WRF Model over the Lake Victoria Basin, Eastern Africa on Seasonal Timescales

Lake Victoria, Africa, supports millions of people. To produce reliable climate projections, it is desirable to successfully model the rainfall over the lake accurately. An initial step is taken here with customization of the Weather, Research, and Forecast (WRF) model. Of particular interest is an asymmetrical rainfall pattern across the lake basin, due to a diurnal land-lake breeze. The main aim is to present a customization framework for use over the lake. This framework is developed by conducting several series of model runs to investigate aspects of the customization. The runs are analyzed using Tropical Rainfall Measuring Mission rainfall data and Climatic Research Unit temperature data. The study shows that the choice of parameters and lake surface temperature initialization can significantly alter the results. Also, the optimal physics combinations for the climatology may not necessarily be suitable for all circumstances, such as extreme years. The study concludes that WRF is unable to reproduce the pattern across the lake. The temperature of the lake is too cold and this prevents the diurnal land-lake breeze reversal. Overall, this study highlights the importance of customizing a model to the region of research and presents a framework through which this may be achieved.

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Simulated Physical Mechanisms Associated with Climate Variability over Lake Victoria Basin in East Africa

Monthly Weather Review ◽

10.1175/mwr3266.1 ◽

2006 ◽

Vol 134 (12) ◽

pp. 3588-3609 ◽

Cited By ~ 74

Author(s):

Richard O. Anyah ◽

Fredrick H. M. Semazzi ◽

Lian Xie

Keyword(s):

Large Scale ◽

Lake Victoria ◽

Early Morning ◽

Lake Basin ◽

Lake Breeze ◽

Lake Surface ◽

Lake Victoria Basin ◽

Diurnal Variability ◽

Physical Mechanisms ◽

Late Night

Abstract A fully coupled regional climate, 3D lake modeling system is used to investigate the physical mechanisms associated with the multiscale variability of the Lake Victoria basin climate. To examine the relative influence of different processes on the lake basin climate, a suite of model experiments were performed by smoothing topography around the lake basin, altering lake surface characteristics, and reducing or increasing the amount of large-scale moisture advected into the lake region through the four lateral boundaries of the model domain. Simulated monthly mean rainfall over the basin is comparable to the satellite (Tropical Rainfall Measuring Mission) estimates. Peaks between midnight and early morning hours characterize the simulated diurnal variability of rainfall over the four quadrants of the lake, consistent with satellite estimates, although the simulated peaks occur a little earlier. It is evident in the simulations with smoothed topography that the upslope/downslope flow generated by the mountains east of the lake and the land–lake breeze circulations play important roles in influencing the intensity, the location of lake/land breeze fronts, and the horizontal extent of the land–lake breeze circulation, as well as lake basin precipitation. When the lake surface is replaced with marsh (water hyacinth), the late night and early morning rainfall maximum located over the western sector of the lake is dramatically reduced. Our simulations also indicate that large-scale moisture transported via the prevailing easterly trades enhances lake basin precipitation significantly. This is in contrast to the notion advanced in some of the previous studies that Lake Victoria generates its own climate (rainfall) through precipitation–evaporation–reprecipitation recycling only.

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Environments and trypanosomiasis risks for early herders in the later Holocene of the Lake Victoria basin, Kenya

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1423953112 ◽

2015 ◽

Vol 112 (12) ◽

pp. 3674-3679 ◽

Cited By ~ 31

Author(s):

Kendra L. Chritz ◽

Fiona B. Marshall ◽

M. Esperanza Zagal ◽

Francis Kirera ◽

Thure E. Cerling

Keyword(s):

Southern Africa ◽

Tooth Enamel ◽

Lake Victoria ◽

Isotope Analysis ◽

Tsetse Fly ◽

Eastern Africa ◽

Tsetse Flies ◽

Lake Victoria Basin ◽

And Migration ◽

Pastoral Neolithic

Specialized pastoralism developed ∼3 kya among Pastoral Neolithic Elmenteitan herders in eastern Africa. During this time, a mosaic of hunters and herders using diverse economic strategies flourished in southern Kenya. It has been argued that the risk for trypanosomiasis (sleeping sickness), carried by tsetse flies in bushy environments, had a significant influence on pastoral diversification and migration out of eastern Africa toward southern Africa ∼2 kya. Elmenteitan levels at Gogo Falls (ca. 1.9–1.6 kya) preserve a unique faunal record, including wild mammalian herbivores, domestic cattle and caprines, fish, and birds. It has been suggested that a bushy/woodland habitat that harbored tsetse fly constrained production of domestic herds and resulted in subsistence diversification. Stable isotope analysis of herbivore tooth enamel (n = 86) from this site reveals, instead, extensive C4 grazing by both domesticates and the majority of wild herbivores. Integrated with other ecological proxies (pollen and leaf wax biomarkers), these data imply an abundance of C4 grasses in the Lake Victoria basin at this time, and thus little risk for tsetse-related barriers to specialized pastoralism. These data provide empirical evidence for the existence of a grassy corridor through which small groups of herders could have passed to reach southern Africa.

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Surrogate climate change projections for the Lake Victoria region with a convection-permitting model.

10.5194/egusphere-egu2020-13559 ◽

2020 ◽

Author(s):

Jonas Van de Walle ◽

Oscar Brousse ◽

Roman Brogli ◽

Matthias Demuzere ◽

Wim Thiery ◽

...

Keyword(s):

Climate Change ◽

Lake Victoria ◽

Climate Extremes ◽

Extreme Weather ◽

Climate Projections ◽

Lake Victoria Basin ◽

Complex Behaviour ◽

Severe Thunderstorms ◽

Ensemble Mean ◽

The Impact

Extreme weather is posing constant threat to more than 30 million people living near Lake Victoria or depending on its resources. Thousands of fishermen die every year by severe thunderstorms and associated water currents, while hazardous over-land thunderstorms largely affect people living inland, continuously facing flood risks. These risks call for better understanding of such climate extremes over the region. Climate models are a useful tool to gain insight in the complex behaviour of thunderstorms, especially when simulated at convection-permitting resolution. Such simulations, explicitly resolving deep convection at fine resolutions, have been shown to improve the representation of extreme events in many parts of the world, also in equatorial East-Africa (Finney et al., 2019; Kendon et al., 2019; Van de Walle et al., 2019). As a response, the CORDEX-Flagship Pilot Study &#8220;climate extremes in the Lake Victoria basin&#8221; (ELVIC) initiative is currently setting up an ensemble of convection-permitting simulations over the region.At this stage, future climate projections are needed to assess the impact of anthropogenic climate change on extreme weather the region. Therefore, a surrogate global warming approach following Sch&#228;r et al. (1996), Kr&#246;ner et al. (2016), Liu et al. (2016) and Rasmussen et al. (2017) has been applied to a convection-permitting COSMO-CLM simulation. In this approach, the lateral boundary conditions from the ERA5 (~31 km resolution) reanalysis are perturbed in accordance with the recent CMIP6 ensemble-mean end-of-century SSP5 8.5 climate change scenario. This approach confers three major advantages over the more conventional methods. First, by perturbing with the ensemble-mean, it excludes uncertainties of GCMs without the need for a time and computational intensive high resolution ensemble approach. Second, it avoids including present-day circulation biases. Third, no intermediate nesting steps are necessary, as the perturbed ERA5 allows a direct downscaling to the convection-permitting climate projection.Besides the methodology, results for the Lake Victoria basin will be presented. Although the occurrence of extreme over-lake precipitation in the present-day climate is mostly controlled by large- and mesoscale atmospheric dynamics (Van de Walle et al., 2019), its future intensification is mainly attributed to increased humidity (Thiery et al., 2016). Furthermore, the effect of changed large-scale dynamics is assessed, as not only temperature and humidity, but also wind forcing is modified.

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Uncertainty in calibrating generalised Pareto distribution to rainfall extremes in Lake Victoria basin

Hydrology Research ◽

10.2166/nh.2014.052 ◽

2014 ◽

Vol 46 (3) ◽

pp. 356-376 ◽

Cited By ~ 15

Author(s):

Charles Onyutha ◽

Patrick Willems

Keyword(s):

Parameter Estimation ◽

Pareto Distribution ◽

Lake Victoria ◽

Estimation Method ◽

Eastern Africa ◽

Rainfall Time Series ◽

Lake Victoria Basin ◽

Parameter Estimation Method ◽

Rainfall Extremes ◽

Generalised Pareto Distribution

Uncertainty in the calibration of the generalised Pareto distribution (GPD) to rainfall extremes is assessed based on observed and large number of global climate model rainfall time series for nine locations in the Lake Victoria basin (LVB) in Eastern Africa. The class of the GPD suitable for capturing the tail behaviour of the distribution and extreme quantiles is investigated. The best parameter estimation method is selected following comparison of the method of moments, maximum likelihood, L-moments, and weighted linear regression in quantile plots (WLR) to quantify uncertainty in the extreme intensity quantiles by employing the Jackknife method and nonparametric percentile bootstrapping in a combined way. The normal tailed GPD was found suitable. Although the performance of each parameter estimation method was acceptable in a number of evaluation criteria, generally the WLR technique appears to be more robust than others. The difference between upper and lower limits of the 95% confidence intervals expressed as a percentage of the empirical 10-year rainfall intensity quantile ranges from 9.25 up to 59.66%. The assessed uncertainty will be useful in support of risk based planning, design and operation of water engineering and water management applications related to floods in the LVB.

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A Numerical Investigation of the Precipitation over Lake Victoria Basin Using a Coupled Atmosphere-Lake Limited-Area Model

Advances in Meteorology ◽

10.1155/2014/960924 ◽

2014 ◽

Vol 2014 ◽

pp. 1-15 ◽

Cited By ~ 5

Author(s):

Xia Sun ◽

Lian Xie ◽

Fredrick H. M. Semazzi ◽

Bin Liu

Keyword(s):

Lake Victoria ◽

Wrf Model ◽

Coupled System ◽

Ocean Model ◽

Radar Reflectivity ◽

Land Breeze ◽

Limited Area ◽

Precipitation Pattern ◽

Lake Victoria Basin ◽

Lake Temperature

By using a coupled atmosphere-lake model, which consists of the Weather Research and Forecasting (WRF) model and the Princeton Ocean Model (POM), the present study generated realistic lake surface temperature (LST) over Lake Victoria and revealed the prime importance of LST on the precipitation pattern over the Lake Victoria Basin (LVB). A suite of sensitivity experiments was conducted for the selection of an optimal combination of physics options including cumulus, microphysics, and planetary boundary layer schemes for simulating precipitation over the LVB. The WRF-POM coupled system made a great performance on simulating the expected LST, which is featured with eastward temperature gradient as in the real bathymetry of the lake. Under thorough examination of diagnostic analysis, a distinguished diurnal phenomenon has been unveiled. The precipitation mainly occurs during the nocturnal peak between midnight and early in the morning, which is associated with the strong land breeze circulation, when the lake temperature is warmer than the adjacent land. Further exploration of vertical velocity, surface divergence pattern, and maximum radar reflectivity confirms such conjecture. The time-longitude analysis of maximum radar reflectivity over the entire lake also shows a noticeable pattern of dominating westward propagation.

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The Role of the Dominant Modes of Precipitation Variability over Eastern Africa in Modulating the Hydrology of Lake Victoria

Advances in Meteorology ◽

10.1155/2014/516762 ◽

2014 ◽

Vol 2014 ◽

pp. 1-11 ◽

Cited By ~ 11

Author(s):

Kara A. Smith ◽

Fredrick H. M. Semazzi

Keyword(s):

East Africa ◽

Southern Oscillation ◽

Lake Victoria ◽

Rainfall Variability ◽

Precipitation Variability ◽

Eastern Africa ◽

Annual Rainfall ◽

Lake Victoria Basin ◽

The Relationship

Previous water budget studies over Lake Victoria basin have shown that there is near balance between rainfall and evaporation and that the variability of Lake Victoria levels is determined virtually entirely by changes in rainfall since evaporation is nearly constant. The variability of rainfall over East Africa is dominated by El Niño-Southern Oscillation (ENSO); however, the second and third most dominant rainfall climate modes also account for significant variability across the region. The relationship between ENSO and other significant modes of precipitation variability with Lake Victoria levels is nonlinear. This relationship should be studied to determine which modes need to be accurately modeled in order to accurately model Lake Victoria levels, which are important to the hydroelectric industry in East Africa. The objective of this analysis is to estimate the relative contributions of the dominant modes of annual precipitation variability to the modulation of Lake Victoria levels for the present day (1950–2012). The first mode of annual rainfall variability accounts for most of the variability in Lake Victoria levels, while the effects of the second and third modes are negligible even though these modes are also significant over the region.

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Effect of Lake Surface Temperature on the Spatial Distribution and Intensity of the Precipitation over the Lake Victoria Basin

Monthly Weather Review ◽

10.1175/mwr-d-14-00049.1 ◽

2015 ◽

Vol 143 (4) ◽

pp. 1179-1192 ◽

Cited By ~ 17

Author(s):

Xia Sun ◽

Lian Xie ◽

Fredrick Semazzi ◽

Bin Liu

Keyword(s):

Surface Temperature ◽

Lake Victoria ◽

Global Analysis ◽

Wrf Model ◽

Weather Forecast ◽

Rainfall Pattern ◽

Rainfall Simulation ◽

Lake Surface ◽

Lake Victoria Basin ◽

Forecast Models

Abstract A series of sensitivity experiments are performed to investigate the response of precipitation over the Lake Victoria basin (LVB) to the changes of lake surface temperature (LST) using the Weather Research and Forecasting (WRF) Model. It is shown that the default LST initialized from NCEP FNL (Final) Operational Global Analysis is deficient for simulating the rainfall over the LVB. Comparative experiments demonstrate the unambiguous impact of LST on the intensity and pattern of the precipitation over LVB. Intensification/weakening of precipitation over the lake occur with increasing/decreasing LST for both uniform and asymmetrical LST distribution. However, the relationship between rainfall anomalies and LST variations is nonlinear. Replacing the LST directly derived from global weather forecast models by the mean area-averaged LST of Lake Victoria (approximately 24°C) leads to improved rainfall simulation. However, LST with realistic cross-basin gradient is necessary to obtain a rainfall pattern consistent with the observations. The fact that rainfall and wind patterns over the lake are sensitive to LST distribution suggests the need to monitor the mesoscale LST pattern for accurate weather and climate prediction over LVB. It is also found that although the LST distribution exerts significant impact on the observed rainfall pattern, the area and location of the rainband are quite persistent under different LST forcing. This suggests that although the details of the rainfall pattern over LVB are strongly influenced by LST, the broad rainfall pattern is likely controlled by the atmospheric circulation and orography in the region.

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Economical exposition to drought events (1980-2001)

10.29104/wins.l.0116.2018 ◽

2017 ◽

Author(s):

Chloé Meyer

Keyword(s):

World Bank ◽

Standardized Precipitation Index ◽

Research Unit ◽

Precipitation Index ◽

Climatic Research Unit ◽

Columbia University ◽

East Anglia ◽

Gis Modeling ◽

The World Bank ◽

Year 2000

Estimation of the annual economical exposition to drought based on Standardized Precipitation Index. It is based on three sources: 1) A global monthly gridded precipitation dataset obtained from the Climatic Research Unit (University of East Anglia). 2) A GIS modeling of global Standardized Precipitation Index based on Brad Lyon (IRI, Columbia University) methodology. 3) A Global Domestic Product grid for the year 2010, provided by the World Bank. Unit is expected average annual GDP (2007 as the year of reference) exposed in (US $, year 2000 equivalent). For more information, visit: http://preview.grid.unep.ch/ Cost Drought Exposure Risk

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Hydrologic evaluation and effects of climate change on the Nong Han Lake Basin, northeastern Thailand

Journal of Water and Climate Change ◽

10.2166/wcc.2019.040 ◽

2019 ◽

Vol 11 (4) ◽

pp. 992-1000

Author(s):

Jirawat Supakosol ◽

Kowit Boonrawd

Keyword(s):

Climate Change ◽

Assessment Tool ◽

Swat Model ◽

Climate Projections ◽

Lake Basin ◽

Model Soil ◽

Regional Climates ◽

Water Assessment ◽

Effective Water ◽

Northeastern Thailand

Abstract The purpose of this study is to investigate the future runoff into the Nong Han Lake under the effects of climate change. The hydrological model Soil and Water Assessment Tool (SWAT) has been selected for this study. The calibration and validation were performed by comparing the simulated and observed runoff from gauging station KH90 for the period 2001–2003 and 2004–2005, respectively. Future climate projections were generated by Providing Regional Climates for Impacts Studies (PRECIS) under the A2 and B2 scenarios. The SWAT model yielded good results in comparison to the baseline; moreover, the results of the PRECIS model showed that both precipitations and temperatures increased. Consequently, the amount of runoff calculated by SWAT under the A2 and B2 scenarios was higher than that for the baseline. In addition, the amount of runoff calculated considering the A2 scenario was higher than that considering the B2 scenario, due to higher average annual precipitations in the former case. The methodology and results of this study constitute key information for stakeholders, especially for the development of effective water management systems in the lake, such as designing a rule curve to cope with any future incidents.

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Sensitivity of projected climate impacts to climate model weighting: multi-sector analysis in eastern Africa

Climatic Change ◽

10.1007/s10584-021-02991-8 ◽

2021 ◽

Vol 164 (3-4) ◽

Author(s):

Seshagiri Rao Kolusu ◽

Christian Siderius ◽

Martin C. Todd ◽

Ajay Bhave ◽

Declan Conway ◽

...

Keyword(s):

Climate Models ◽

Climate Model ◽

Investment Decisions ◽

Climate Impacts ◽

Future Climate ◽

Eastern Africa ◽

Climate Projections ◽

Systematic Effect ◽

Risk Profiles ◽

Model Weighting

AbstractUncertainty in long-term projections of future climate can be substantial and presents a major challenge to climate change adaptation planning. This is especially so for projections of future precipitation in most tropical regions, at the spatial scale of many adaptation decisions in water-related sectors. Attempts have been made to constrain the uncertainty in climate projections, based on the recognised premise that not all of the climate models openly available perform equally well. However, there is no agreed ‘good practice’ on how to weight climate models. Nor is it clear to what extent model weighting can constrain uncertainty in decision-relevant climate quantities. We address this challenge, for climate projection information relevant to ‘high stakes’ investment decisions across the ‘water-energy-food’ sectors, using two case-study river basins in Tanzania and Malawi. We compare future climate risk profiles of simple decision-relevant indicators for water-related sectors, derived using hydrological and water resources models, which are driven by an ensemble of future climate model projections. In generating these ensembles, we implement a range of climate model weighting approaches, based on context-relevant climate model performance metrics and assessment. Our case-specific results show the various model weighting approaches have limited systematic effect on the spread of risk profiles. Sensitivity to climate model weighting is lower than overall uncertainty and is considerably less than the uncertainty resulting from bias correction methodologies. However, some of the more subtle effects on sectoral risk profiles from the more ‘aggressive’ model weighting approaches could be important to investment decisions depending on the decision context. For application, model weighting is justified in principle, but a credible approach should be very carefully designed and rooted in robust understanding of relevant physical processes to formulate appropriate metrics.

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