scholarly journals Implications of Improved Representation of Convection for the East Africa Water Budget Using a Convection-Permitting Model

2019 ◽  
Vol 32 (7) ◽  
pp. 2109-2129 ◽  
Author(s):  
Declan L. Finney ◽  
John H. Marsham ◽  
Lawrence S. Jackson ◽  
Elizabeth J. Kendon ◽  
David P. Rowell ◽  
...  
Keyword(s):  
East Africa ◽  
Water Budget ◽  
Large Scale ◽  
Lake Victoria ◽  
Regional Climate ◽  
Moisture Flux ◽  
Land Breeze ◽  
Moist Convection ◽  
Atmospheric Water ◽  
Lake Victoria Basin

Abstract The precipitation and diabatic heating resulting from moist convection make it a key component of the atmospheric water budget in the tropics. With convective parameterization being a known source of uncertainty in global models, convection-permitting (CP) models are increasingly being used to improve understanding of regional climate. Here, a new 10-yr CP simulation is used to study the characteristics of rainfall and atmospheric water budget for East Africa and the Lake Victoria basin. The explicit representation of convection leads to a widespread improvement in the intensities and diurnal cycle of rainfall when compared with a parameterized simulation. Differences in large-scale moisture fluxes lead to a shift in the mean rainfall pattern from the Congo to Lake Victoria basin in the CP simulation—highlighting the important connection between local changes in the representation of convection and larger-scale dynamics and rainfall. Stronger lake–land contrasts in buoyancy in the CP model lead to a stronger nocturnal land breeze over Lake Victoria, increasing evaporation and moisture flux convergence (MFC), and likely unrealistically high rainfall. However, for the mountains east of the lake, the CP model produces a diurnal rainfall cycle much more similar to satellite estimates, which is related to differences in the timing of MFC. Results here demonstrate that, while care is needed regarding lake forcings, a CP approach offers a more realistic representation of several rainfall characteristics through a more physically based realization of the atmospheric dynamics around the complex topography of East Africa.

scholarly journals Identifying Key Controls on Storm Formation over the Lake Victoria Basin

2019 ◽  
Vol 147 (9) ◽  
pp. 3365-3390 ◽  
Author(s):  
Beth J. Woodhams ◽  
Cathryn E. Birch ◽  
John H. Marsham ◽  
Todd P. Lane ◽  
Caroline L. Bain ◽  
...  
Keyword(s):  
Large Scale ◽  
Lake Victoria ◽  
Hot Spot ◽  
Land Breeze ◽  
Lake Victoria Basin ◽  
Convective Storms ◽  
Moisture Availability ◽  
Lake Victoria Region ◽  
The Mean ◽  
Horizontal Grid

Abstract The Lake Victoria region in East Africa is a hot spot for intense convective storms that are responsible for the deaths of thousands of fishermen each year. The processes responsible for the initiation, development, and propagation of the storms are poorly understood and forecast skill is limited. Key processes for the life cycle of two storms are investigated using Met Office Unified Model convection-permitting simulations with 1.5 km horizontal grid spacing. The two cases are analyzed alongside a simulation of a period with no storms to assess the roles of the lake–land breeze, downslope mountain winds, prevailing large-scale winds, and moisture availability. While seasonal changes in large-scale moisture availability play a key role in storm development, the lake–land-breeze circulation is a major control on the initiation location, timing, and propagation of convection. In the dry season, opposing offshore winds form a bulge of moist air above the lake surface overnight that extends from the surface to ~1.5 km and may trigger storms in high CAPE/low CIN environments. Such a feature has not been explicitly observed or modeled in previous literature. Storms over land on the preceding day are shown to alter the local atmospheric moisture and circulation to promote storm formation over the lake. The variety of initiation processes and differing characteristics of just two storms analyzed here show that the mean diurnal cycle over Lake Victoria alone is inadequate to fully understand storm formation. Knowledge of daily changes in local-scale moisture variability and circulations are keys for skillful forecasts over the lake.

A coupled regional climate model for the Lake Victoria basin of East Africa

2004 ◽  
Vol 24 (1) ◽  
pp. 57-75 ◽  
Author(s):  
Yi Song ◽  
Fredrick H. M. Semazzi ◽  
Lian Xie ◽  
Laban J. Ogallo
Keyword(s):  
Regional Climate Model ◽  
East Africa ◽  
Climate Model ◽  
Lake Victoria ◽  
Regional Climate ◽  
Lake Victoria Basin

scholarly journals Prolific Lightning and Thunderstorm Initiation over the Lake Victoria Basin in East Africa

2020 ◽  
Vol 148 (5) ◽  
pp. 1971-1985 ◽  
Author(s):  
Katrina S. Virts ◽  
Steven J. Goodman
Keyword(s):  
East Africa ◽  
Hot Spots ◽  
Seasonal Cycle ◽  
Lake Victoria ◽  
Intertropical Convergence Zone ◽  
Lake Victoria Basin ◽  
The Earth ◽  
Total Lightning ◽  
Average Cluster

Abstract The Lake Victoria basin of East Africa is home to over 30 million people, over 200 000 of whom are employed in fishing or transportation on the lake. Approximately 3000–5000 individuals are killed by thunderstorms yearly, primarily by outflow winds and resulting large waves. Prolific lightning activity and thunderstorm initiation in the basin are examined using continuous total lightning observations from the Earth Networks Global Lightning Network (ENGLN) for September 2014–August 2018. Seasonal shifts in the intertropical convergence zone produce semiannual lightning maxima over the lake. Diurnally, solar heating and lake and valley breezes produce daytime lightning maxima north and east of the lake, while at night the peak lightning density propagates southwestward across the lake. Cluster analysis reveals terrain-related thunderstorm initiation hot spots northeast of the lake; clusters also initiate over the lake and northern lowlands. The most prolific clusters initiate between 1100 and 1400 LT, about 1–2 h earlier than the average cluster. Most daytime thunderstorms dissipate without reaching Lake Victoria, and annually 85% of clusters producing over 1000 flashes over Lake Victoria initiate in situ. Initiation times of prolific Lake Victoria clusters exhibit a bimodal seasonal cycle: equinox-season thunderstorms initiate most frequently between 2200 and 0400 LT, while solstice-season thunderstorms initiate most frequently from 0500 to 0800 LT, more than 12 h after the afternoon convective peak over land. More extreme clusters are more likely to have formed over land and propagated over the lake, including 36 of the 100 most extreme Lake Victoria thunderstorms. These mesoscale clusters are most common during February–April and October–November.

scholarly journals The Effect of Explicit Convection on Couplings between Rainfall, Humidity, and Ascent over Africa under Climate Change

2020 ◽  
Vol 33 (19) ◽  
pp. 8315-8337 ◽  
Author(s):  
Lawrence S. Jackson ◽  
Declan L. Finney ◽  
Elizabeth J. Kendon ◽  
John H. Marsham ◽  
Douglas J. Parker ◽  
...  
Keyword(s):  
Climate Change ◽  
Large Scale ◽  
Climate Models ◽  
Regional Climate ◽  
Hadley Circulation ◽  
Moist Convection ◽  
Rain Belt ◽  
Adaptation To Climate Change ◽  
Convective Scale ◽  
Mean Climate

AbstractThe Hadley circulation and tropical rain belt are dominant features of African climate. Moist convection provides ascent within the rain belt, but must be parameterized in climate models, limiting predictions. Here, we use a pan-African convection-permitting model (CPM), alongside a parameterized convection model (PCM), to analyze how explicit convection affects the rain belt under climate change. Regarding changes in mean climate, both models project an increase in total column water (TCW), a widespread increase in rainfall, and slowdown of subtropical descent. Regional climate changes are similar for annual mean rainfall but regional changes of ascent typically strengthen less or weaken more in the CPM. Over a land-only meridional transect of the rain belt, the CPM mean rainfall increases less than in the PCM (5% vs 14%) but mean vertical velocity at 500 hPa weakens more (17% vs 10%). These changes mask more fundamental changes in underlying distributions. The decrease in 3-hourly rain frequency and shift from lighter to heavier rainfall are more pronounced in the CPM and accompanied by a shift from weak to strong updrafts with the enhancement of heavy rainfall largely due to these dynamic changes. The CPM has stronger coupling between intense rainfall and higher TCW. This yields a greater increase in rainfall contribution from events with greater TCW, with more rainfall for a given large-scale ascent, and so favors slowing of that ascent. These findings highlight connections between the convective-scale and larger-scale flows and emphasize that limitations of parameterized convection have major implications for planning adaptation to climate change.

Regional climate model performance in the Lake Victoria basin

2014 ◽  
Vol 44 (5-6) ◽  
pp. 1699-1713 ◽  
Author(s):  
Karina Williams ◽  
Jill Chamberlain ◽  
Carlo Buontempo ◽  
Caroline Bain
Keyword(s):  
Regional Climate Model ◽  
Climate Model ◽  
Lake Victoria ◽  
Regional Climate ◽  
Model Performance ◽  
Lake Victoria Basin

The characteristics and drivers of climatological precipitation over the Serengeti-Mara region

2020 ◽  
Author(s):  
Josephine Mahony ◽  
Ellen Dyer ◽  
Richard Washington
Keyword(s):  
Annual Cycle ◽  
Large Scale ◽  
Lake Victoria ◽  
Basic Structure ◽  
Local Source ◽  
Land Breeze ◽  
Rainfall Gradient ◽  
Annual Cycles ◽  
Precipitation Patterns ◽  
And Cluster Analysis

<p>The Serengeti National Park is famous for the biological phenomenon of the annual wildebeest migration. This migration is reliant on unique local precipitation conditions: a rainfall gradient stretching across the park, the strength and inclination of which alters from month to month. Given the ecological significance and the complexity of the regional precipitation, a detailed study of the region’s climatology is essential for understanding why these precipitation patterns exist, and whether they are likely to change.</p><p>Using multiple observational datasets, we studied the spatial distribution of annual and monthly climatological precipitation. We carried out harmonic analysis and cluster analysis to identify areas with similar annual cycles. We then examined regional wind, moisture and precipitation patterns on seasonal, monthly and diurnal timescales.</p><p>We found that the large-scale wind circulation patterns dictate the basic structure of the annual cycle over the region. However the shape of the annual cycle was distinctly different in 5 parts of the region, with varying peak rainfall months and dry season rainfall totals. Analysis of the diurnal wind patterns showed that the regional seasonality is strongly augmented by the lake and land breeze from Lake Victoria, and the interactions between this local source of moisture and the complex topography of the East African rift. This leads to a low-level convergence zone between the prevailing large-scale easterlies, and westerlies from Lake Victoria over the Serengeti in the afternoon. This in turn results in the rainfall gradient across the region, the orientation of which changes depending on the mid-tropospheric wind direction.</p>

Scaling-up sustainable intensification practices for rice production in East Africa

2020 ◽  
Author(s):  
Robert Burtscher ◽  
Taher Kahil ◽  
Mikhail Smilovic ◽  
Diana Luna ◽  
Jenan Irshaid ◽  
...  
Keyword(s):  
East Africa ◽  
Agricultural Production ◽  
Management Practices ◽  
Lake Victoria ◽  
Rice Production ◽  
Sustainable Intensification ◽  
Food Demand ◽  
Suitability Analysis ◽  
Lake Victoria Basin ◽  
Modeling Framework

<p>Food security has long been a challenge for East Africa region and is becoming a pressing issue for the coming decades because food demand is expected to increase considerably following rapid population and income growth. Agricultural production in the region is thus required to intensify, in a sustainable way, to keep up with food demand. However, many challenges face the sustainable intensification of the agricultural production including low productivity, inadequate management, small scale operations, and large climate variability. Several pilot initiatives, that involves a bundle of land and water management practices, have been introduced in the region to tackle such challenges. However, their large-scale implementation remains limited. In the framework of a research project which is jointly implemented by the International Institute for Applied System Analysis (IIASA), the Lake Victoria Basin Commission (LVBC) and the International Crops Research Institute for Semi-Arid Tropics (ICRISAT), we analyse up scaling opportunities for water and land management practices for the sustainable and resilient intensification of rice and fodder production systems in the extended Lake Victoria Basin in East Africa. The expected outcome of this project is to provide an improved understanding of up scaling of such practices through model simulations and integrated analysis of political economy aspects, governance and social and gender dimensions.</p><p>This paper presents an integrated upscaling modeling framework that combines biophysical suitability analysis and economic optimization. Several production system options (i.e., management practices) for rice intensification are examined at high-spatial resolution (0.5°x0.5°) in the extended Lake Victoria basin. The suitability analysis identifies suitable area for the production system options based on a combination of various biophysical factors such as climate, hydrology, vegetation and soil properties using the Global Agroecological Zones (GAEZ) model and the Community Water Model (CWaTM). The economic optimization identifies the optimal combination of those production systems that maximizes their overall contribution to agricultural economic benefits having satisfied various technical and resource constraints including commodity balance, land availability and suitability, water availability, labor availability and capital constraints. A set of socioeconomic (e.g., impact of population and income growth on food demand and agricultural productivity) and climate change (e.g., impact on water resources availability) scenarios based on combinations of the Shared Socioeconomic Pathways (SSPs), Representative Concentration Pathways (RCPs), and co-developed bottom-up policy scenarios, through stakeholders’ engagement with the Basin Commission (LVBC), have been utilized to simulate the modeling framework. Results of this study show the existence of significant opportunities for the sustainable intensification of rice production in East Africa. Moreover, the study identifies the key biophysical and economic factors that could enable the upscaling of sustainable land and water management practices for rice production in the region. Overall, this study demonstrates the capacity of the proposed upscaling modeling framework as a system approach to address the linkages between the intensification of agricultural production and the sustainable use of natural resources.</p>

HydroSOS: a pilot global Hydrological Status and Outlook System integrating national to global scale hydrological services for increased resilience to hydro-climatic risks

2020 ◽  
Author(s):  
Katie Smith ◽  
Luis Roberto Silva Vara ◽  
Harry Dixon ◽  
Victoria Barlow ◽  
Alan Jenkins ◽  
...  
Keyword(s):  
Large Scale ◽  
Lake Victoria ◽  
Pilot Project ◽  
Global Scale ◽  
Lake Victoria Basin ◽  
Scale Modelling ◽  
Technical Specifications ◽  
Climatic Risks ◽  
Main Activity ◽  
Hydrological Services

<p>Consistent hydrological status and outlook information across transboundary basins or regions of shared hydrological interest are not often available. Furthermore, whilst large-scale modelling capabilities are continually improving, there is an information and confidence gap between locally informed hydrological status information products and those developed globally.</p><p>HydroSOS is World Meteorological Organisation initiative that aims to increase global resilience to hydro-climatic risks through the production of hydrological status and outlooks assessments at different scales around the world. Currently in a pilot phase, HydroSOS is being developed through a collaboration between National Hydrometeorological Services, transboundary basin organisations, global modelling centres and the research community. The system will provide an appraisal of where current hydrological status is different from “normal”, as well as sub-seasonal to seasonal outlooks indicating whether this is likely to get better or worse over the coming weeks and months.</p><p>The HydroSOS programme consists of five main activity streams:</p><ol><li>Increasing the interoperability of hydrological status and outlook products through <strong>Common Technical Specifications.</strong></li> <li>Increasing national capabilities to generate hydrological status and sub-seasonal to seasonal outlook products through <strong>Guidance on Methods and Tools.</strong></li> <li>Increasing the utility of large-scale hydrological status and outlook modelling through <strong>Co-design of Global Products</strong>, with international partners working from local to global scale.</li> <li>Increasing shared production of transboundary hydrological status and outlook products through <strong>Regional Pilots</strong>, initially in South Asia and the Lake Victoria Basin.</li> <li>Integration of hydrological status and outlook products for national, regional and global users through a <strong>Demonstration Portal.</strong></li> </ol><p>This PICO contribution will present progress in the pilot project to date, including a hands-on demonstration of the web portal.</p>

Genetically distinct strains of Cassava brown streak virus in the Lake Victoria basin and the Indian Ocean coastal area of East Africa

2009 ◽  
Vol 154 (2) ◽  
pp. 353-359 ◽  
Author(s):  
D. R. Mbanzibwa ◽  
Y. P. Tian ◽  
A. K. Tugume ◽  
S. B. Mukasa ◽  
F. Tairo ◽  
...  
Keyword(s):  
Indian Ocean ◽  
East Africa ◽  
Coastal Area ◽  
Lake Victoria ◽  
Streak Virus ◽  
Lake Victoria Basin ◽  
Cassava Brown Streak Virus ◽  
The Indian Ocean ◽  
Brown Streak
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