Certain aspects of monsoonal precipitation dynamics over Lake Victoria

Datta, R. K.

doi:10.1017/cbo9780511897580.026

Cited by 21 publications

(19 citation statements)

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“…Much less rainfall occurs during daytime and early evening, when the lake breeze ( Figure 5(b) and (c)) is dominant. The simulated diurnal cycle for the precipitation over the lake basin is consistent with the observational analysis of Datta (1981), and our recent results (Song et al, 2002: figure 3) based on the RegCM2 model coupled to a one-dimensional lake model. The RegCM2-POM coupled model simulated rainfall also shows that the maximum over the eastern part of Lake Victoria occurs (d)).…”

Section: Diurnal Cyclesupporting

confidence: 88%

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

Song

Semazzi

Xie

et al. 2004

Intl Journal of Climatology

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A nested coupled model has been developed to investigate the two-way interactions between the regional climate of eastern Africa and Lake Victoria. The atmospheric component of the model is the North Carolina State University (NCSU) version of the National Center for Atmospheric Research (NCAR) regional climate model (NCSU-RegCM2). The lake component of the model is based on the Princeton ocean model (POM).Three simulations, each 4 months long, have been performed for the short rains of eastern Africa of September through to December. The control experiment is based on the standard NCSU-RegCM2 model coupled to a one-dimensional model of Lake Victoria. The second experiment was based on the stand-alone three-dimensional primitive equation POM-Lake Victoria model forced by output from the atmospheric component of the control run. The third experiment is based on the integration of the coupled system of the NCSU-RegCM2 model where the one-dimensional lake model in the control run has been replaced by the three-dimensional POM hydrodynamical model for Lake Victoria.The results confirm that adopting the traditional modelling approach, in which the lake hydrodynamics are neglected and the formulation is based entirely on thermodynamics alone, is not entirely satisfactory for the Lake Victoria basin. Such a strategy precludes the transport of heat realistically within the lake, from the heat surplus regions to the cooler regions, and thereby results in a degraded simulation of the climate downstream over the rest of the lake and the surrounding land regions. The numerical simulations show that the southwestern region of the lake is an important source of warm water because it is relatively shallower and the water column is heated up much more quickly during the day than the rest of the lake. The result is that the surface temperature anomaly field from the all-lake area average consists of a gradient pattern with warmer water over the shallow region of the lake over the southeastern sector and a colder pool of water over the northeastern region, where the lake is relatively deeper. This pattern is also reproduced by the one-dimensional lake model. Some of the excess heat over the southeastern region is transported to the colder and deeper region over the northeastern part of the lake by prevailing surface wind flow. Through the lake-atmosphere coupling, the resulting asymmetric lake-surface temperature distribution modifies the overlying wind circulation, which in turn reduces the cloud cover and rainfall. This secondary feature in the surface temperature structure cannot be generated by the traditional nested climate models, such as the standard version of the NCAR-RegCM2 model, since the simple static lake model formulation is not capable of supporting horizontal mixing of water. Comparisons show that this feature is weaker in the RegCM2-POM coupled model than the corresponding pattern that we obtained in our previous study based on the 'stand-alone' POM lake model. In contrast, from the simple classical tex...

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Section: Diurnal Cyclesupporting

confidence: 88%

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

Song

Semazzi

Xie

et al. 2004

Intl Journal of Climatology

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“…The enhancement of rainfall over the lake and many other aspects of the rainfall regime suggested by Fraedrich's model are supported by the studies of Datta (1981) and Ba & Nicholson (in press). Daily rainfall data show a nocturnal peak in rainfall over the lake's centre and along its western shore, as well as an afternoon peak along the eastern shore (Fig.…”

Section: Water Balancementioning

confidence: 56%

“…The earliest water balance calculations were those of Hurst & Phillips (1933), Hurst (1952) and Merelieu (1961) (see Datta, 1981). Moerth (1967) also studied the relationship between lake level and rainfall.…”

Section: Water Balancementioning

confidence: 99%

See 1 more Smart Citation

The water balance of Lake Victoria

Yin

Nicholson

1998

Hydrological Sciences Journal

141

114

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This paper presents new calculations of Lake Victoria's water balance. Evaporation is estimated using both the Penman formula and the energy balance approach, and sensitivity studies are performed to determine the influence of input data on the estimates. Rainfall over the lake is estimated from catchment rainfall using a relationship between the two that was derived using satellite data. The results, using the reference period 1956-1978, indicate that mean annual rainfall over the lake is 1791 mm, compared to mean annual evaporation of 1551 mm. When compared with lake level changes, tributary inflow, and discharge during this period, there is a resultant imbalance of 19 mm. Adding this amount to the calculated evaporation, we are able to reproduce with great accuracy the lake level changes during the period 1956-1978 utilizing precipitation estimates of this study plus measured inflow and discharge. Sensitivity studies show that the discrepancy in the balance of 19 mm is considerably smaller than the error in evaporation calculations that can be introduced by uncertainties in the input data. Of particular concern is cloudiness. The diurnal cycle of cloudiness is quite different over the lake than at shoreline stations and the total cloud cover over the lake is probably lower than at these stations. A change from 50% cloudiness to 30% can increase evaporation by about 30%. Thus, this study underscores the need for adequate cloud data, sufficient to resolve the diurnal cycle, as well as direct estimates of lake rainfall in assessing the lake's water balance. Le bilan hydrologique du Lac VictoriaRésumé Ce papier présente de nouveaux calculs du bilan hydrologique du Lac Victoria. L'évaporation est estimée par la formule de Penman et la méthode du bilan énergétique. Une étude de sensibilité a été entreprise pour déterminer l'influence des données d'entrée sur les estimations. Les précipitations sur le lac ont été calculées à partir de données satellitaires utilisant une relation établie entre la pluie sur le lac et celle du bassin versant. Les résultats, basés sur une période de référence allant de 1956 à 1978, indiquent que la moyenne des précipitations annuelles sur le lac est égale à 1791 mm, comparée à une moyenne annuelle de l'évaporation égale à 1551 mm. Une comparaison avec les modifications du niveau du lac, les écoulements et débits pendant cette période indique un surplus de 19 mm. Lorsque cette hauteur est ajoutée à l'évaporation calculée, on arrive à reproduire très exactement les fluctuations du lac de 1956 à 1978, en utilisant les précipitations estimées sur le lac ainsi que les débits et les écoulements mesurés. Les études de sensibilité montrent que l'erreur de 19 mm sur le bilan hydrologique est nettement inférieure à celle induite dans les calculs de l'évaporation en raison des incertitudes sur les données d'entrée. La nébulosité reste un problème majeur car son cycle diurne est sensiblement différent sur le lac et sur les stations côtières, la nébulosité totale sur le lac étant probableme...

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“…Water balance studies of Lake Victoria have shown that the increase in lake levels was largely due to extremely high rainfall over the lake and catchment in ON 1961 followed by three further wet years in 1962, 1963and 1964. Piper et al (1986 found it was not possible, however, to account fully for the rise in lake levels using a water balance approach because their estimate of lake rainfall, which was calculated from an average of eight lakeside gauges, tended to underestimate over-lake rainfall (Datta, 1981). This underestimate has recently been confirmed by Nicholson et al (2000) using satellite cold-cloud data to estimate rainfall over the lake and land area.…”

Section: The Persistence Of High Lake Victoria Levels After 1961mentioning

confidence: 99%

Extreme Rainfall Events and Lake Level Changes in East Africa: Recent Events and Historical Precedents

Conway

2002

Advances in Global Change Research

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Certain aspects of monsoonal precipitation dynamics over Lake Victoria

Cited by 21 publications

References 0 publications

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

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

The water balance of Lake Victoria

Extreme Rainfall Events and Lake Level Changes in East Africa: Recent Events and Historical Precedents

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