The Characteristics of Wet Spells in Tanzania

Ogallo, Laban; Chillambo, W A

doi:10.1080/00128325.1981.11663089

Cited by 7 publications

(7 citation statements)

References 13 publications

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“…In this study, a 1.0 mm threshold is used to delineate the wet days from the dry ones. Lower thresholds (less than 1.0 mm) are more vulnerable to measurement errors associated with light rainfall and readily evaporate given the higher evapo‐transpiration rate at the study region (Ogallo and Chillambo, ; Douguedroit, ; Lazaro et al ., ; Frei et al ., ).…”

Section: Methodsmentioning

confidence: 99%

Spatial coherence and potential predictability assessment of intraseasonal statistics of wet and dry spells over Equatorial Eastern Africa

Gitau¹,

Ogallo

Camberlin

et al. 2012

Intl Journal of Climatology

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ABSTRACT:The aim of this study was to derive components of the intraseasonal rainfall variations from the daily rainfall in the Equatorial Eastern Africa region and assess their spatial coherence, a pointer to their potential predictability. Daily rainfall observations from 36 stations distributed over Equatorial Eastern Africa and extending from 1962 to 2000 were used. The March to May and October to December periods commonly referred to as the long and short rainfall seasons respectively were considered.Seasonal and intraseasonal statistics at the local (station) level were first defined. The stations were also grouped into near-homogeneous (sub-regional) zones based on daily rainfall. Similarly, seasonal and intraseasonal statistics were then derived at sub-regional level using three different approaches. Inter-station correlation coefficients of the intraseasonal statistics at local levels were finally computed and plotted as box-plots.For the two rainfall seasons, the two statistics showing the highest spatial coherence were the seasonal rainfall totals and the number of the wet days at sub-regional level. The local variance explained for these two variables, as an average over all the sub-regions, was more than 40%. At the bottom of the hierarchy were the mean rainfall intensity and frequency of dry spells of 5 days or more which showed the least coherence, with the local variance explained being less than 10% in each season. For each of the intraseasonal components of daily rainfall considered, the short rainfall season statistics were more coherent compared to the long rainfall season. Lag-correlations with key indices depicting sea-surface temperatures in the Pacific and Indian Oceans showed that the hierarchy between the rainfall statistics in the strength of the teleconnections reflected that of spatial coherence.

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Section: Methodsmentioning

confidence: 99%

Spatial coherence and potential predictability assessment of intraseasonal statistics of wet and dry spells over Equatorial Eastern Africa

Gitau¹,

Ogallo

Camberlin

et al. 2012

Intl Journal of Climatology

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“…In evaluating the skill of WRF to simulate the wet days and wet spells, a wet day was defined as a day having accumulated precipitation of more than 1mm [22,33]. The wet spell is defined as a period of k continuous rainy days having rainfall greater than 1 mm [15,20,33]. This was done using the INSTAT software [36].…”

Section: Methodsmentioning

confidence: 99%

“…Omondi et al [4] observed that there is an increase in the frequency of droughts over in the horn of Africa in recent years. This has been linked to the global climate change [11][12][13], which has been associated with the spatial and temporal decline in rainfall [14][15][16][17] and also increased the number of cases of food insecurity and resource based conflicts [18][19][20]. In this regard, timely information on the spatio-temporal rainfall patterns is essential for effectively managing the rainfall dependent socio-economic sectors and for disaster risk reduction.…”

Section: Introductionmentioning

confidence: 99%

Analysis of WRF Simulation Skill for Seasonal Rainfall: A Case Study of 2015 September–November Season

R¹,

Mugume²

2019

Preprint

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Rainfall is a major climate parameter whose variation in space and time influences activities in different weather sensitive sectors such as agriculture, transport, and energy among others. Therefore, accurately forecasting rainfall is of paramount importance to the development of these sectors. In this regard, this study sought to contribute to quantitative forecasting of rainfall over Eastern Uganda through assessing the Weather Research and Forecasting model's ability to simulate the intra-seasonal characteristics of the September to December rain season. These were: onset and cessation dates; wet days and lengths of the wet spells. The data used in the study included daily ground rainfall observations and lateral and boundary conditions data from the National Centers for Environmental Prediction (NCEP) final analysis at 1 0 horizontal resolution and at a temporal resolution of 6 hours for the entire study period were used to initialize the Weather Research and Forecasting (WRF) model. The study considered four weather synoptic weather stations namely; Jinja, Serere, Soroti and Tororo. The results show that the WRF model generally simulated fewer wet days at each station except for Tororo. Also, the WRF model simulated earlier onset and cessation dates of the rainfall season and overestimated the length of the wet spells.

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“…A threshold of 1.0 mm was used to delineate wet days from dry days (Gitau et al, 2013(Gitau et al, , 2015. Lower thresholds were not considered due to possible measurement errors associated with light rainfall that may readily evaporate given the high evapo-transpiration rate at the study region (Ogallo and Chillambo, 1982;Douguedroit, 1987;Lazaro et al, 2001;Frei et al, 2003;Gitau et al, 2013Gitau et al, , 2015.…”

Section: Derivation Of Intraseasonal Descriptors At Local and Sub-regmentioning

confidence: 99%

“…A local definition of wet and dry spells was adopted, as in previous studies (Ogallo and Chillambo, 1982;Gitau et al, 2008Gitau et al, , 2013Gitau et al, , 2015. They defined a wet (dry) spell of length i as a sequence of i wet (dry) days preceded and followed by a dry (wet) day.…”

Section: Derivation Of Intraseasonal Descriptors At Local and Sub-regmentioning

confidence: 99%

Trends of intraseasonal descriptors of wet and dry spells over equatorial eastern Africa

Gitau

Camberlin

Ogallo

et al. 2017

Intl Journal of Climatology

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Many African countries whose economies are largely based on weather/climate sensitive sectors are vulnerable to long‐term changes in weather and climate. This study is aimed at assessing whether the recent decades have observed any significant trend in the intraseasonal descriptors (ISDs) of wet and dry spells at local and sub‐regional levels at seasonal and monthly timescales over equatorial eastern Africa (EEA). Daily rainfall observations over 36 stations and spanning a period of 51 years (1962–2012) were used. The study has expanded on previous results that showed contrasting trends on seasonal totals between the two rainfall seasons by demonstrating that this also affects the ISDs. At the local level, it was observed that during the long rainfall season, a given ISD would have a significant trend over several neighbouring locations, which was not the case during the short rainfall season. Secondly, for the short rainfall season, a given location would have significant trend in several ISDs. Finally, when a given ISD had a significant trend at seasonal timescale during the long rainfall season, the same ISD would have significant trends in the second and third months of the season and rarely in the first month. Such a feature was not observed for the short rainfall season. Binomial probability distribution assessment confirmed that the significant trends in the various ISDs during the long rainfall season did not occur by mere chance.

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The Characteristics of Wet Spells in Tanzania

Cited by 7 publications

References 13 publications

Spatial coherence and potential predictability assessment of intraseasonal statistics of wet and dry spells over Equatorial Eastern Africa

Spatial coherence and potential predictability assessment of intraseasonal statistics of wet and dry spells over Equatorial Eastern Africa

Analysis of WRF Simulation Skill for Seasonal Rainfall: A Case Study of 2015 September–November Season

Trends of intraseasonal descriptors of wet and dry spells over equatorial eastern Africa

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The Characteristics of Wet Spells in Tanzania

Cited by 7 publications

References 13 publications

Spatial coherence and potential predictability assessment of intraseasonal statistics of wet and dry spells over Equatorial Eastern Africa

Spatial coherence and potential predictability assessment of intraseasonal statistics of wet and dry spells over Equatorial Eastern Africa

Analysis of WRF Simulation Skill for Seasonal Rainfall: A Case Study of 2015 September&ndash;November Season

Trends of intraseasonal descriptors of wet and dry spells over equatorial eastern Africa

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Analysis of WRF Simulation Skill for Seasonal Rainfall: A Case Study of 2015 September–November Season