Browsing by Author "Amekudzi, Leonard K."
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- ItemAssessing Climate Driven Malaria Variability in Ghana Using a Regional Scale Dynamical Model(Climate, 2017-03-05) Asare, Ernest O.; Amekudzi, Leonard K.Malaria is a major public health challenge in Ghana and adversely affects the productivity and economy of the country. Although malaria is climate driven, there are limited studies linking climate variability and disease transmission across the various agro-ecological zones in Ghana. We used the VECTRI (vector-borne disease community model of the International Centre for Theoretical Physics, Trieste) model with a new surface hydrology scheme to investigate the spatio-temporal variability in malaria transmission patterns over the four agro-ecological zones in Ghana. The model is driven using temperature and rainfall datasets obtained from the GMet (Ghana Meteorological Agency) synoptic stations between 1981 and 2010. In addition, the potential of the VECTRI model to simulate seasonal pattern of local scale malaria incidence is assessed. The model results reveal that the simulated malaria transmission follows rainfall peaks with a two-month time lag. Furthermore, malaria transmission ranges from eight to twelve months, with minimum transmission occurring between February and April. The results further reveal that the intra- and inter-agro-ecological variability in terms of intensity and duration of malaria transmission are predominantly controlled by rainfall. The VECTRI simulated EIR (Entomological Inoculation Rate) tends to agree with values obtained from field surveys across the country. Furthermore, despite being a regional model, VECTRI demonstrates useful skill in reproducing monthly variations in reported malaria cases from Emena hospital (a peri urban town located within Kumasi metropolis). Although further refinements in this surface hydrology scheme may improve VECTRI performance, VECTRI still possesses the potential to provide useful information for malaria control in the tropics
- ItemA breeding site model for regional, dynamical malaria simulations evaluated using in situ temporary ponds observations(Geospatial Health, 2016) Asare, Ernest O.; Tompkins, Adrian M.; Amekudzi, Leonard K.; Ermert, VolkerDaily observations of potential mosquito developmental habitats in a suburb of Kumasi in central Ghana reveal a strong variability in their water persistence times, which ranged between 11 and 81 days. The persistence of the ponds was strongly tied with rainfall, location and size of the puddles. A simple power-law relationship is found to fit the relationship between the average pond depth and area well. A prognostic water balance model is derived that describes the temporal evolution of the pond area and depth, incorporating the power-law geometrical relation. Pond area increases in response to rainfall, while evaporation and infiltration act as sink terms. Based on a range of evaluation metrics, the prognostic model is judged to provide a good representation of the pond coverage evolution at most sites. Finally, we demonstrate that the prognostic equation can be generalised and equally applied to a grid-cell to derive a fractional pond coverage, and thus can be implemented in spatially distributed models for relevant vector-borne diseases such as malaria
- ItemComparison of gauge rainfall measurements with TRMM satellite estimates over Kumasi(CCPOP, 2015-07-29) Amekudzi, Leonard K.; Osei, Marian A.; Ahiataku, Maureen A.; Oduro, Magaret A.; Asante-Bekoe, EugeneRainfall is an essential resource for socio-economic activities especially in developing countries. I Rainfall variability in Sub-Saharan Africa has been reported by Owusu et al. (2012), Nicholson et al. (2003), Amekudzi et al. (2015). I To improve our understanding of the spatio-temporal variations of rainfall rigourous validation has been carried out all over the world by comparing in-situ measurements with satellite estimates. (Friesen 2002; Amekudzi et al., 2011; Adeyewa and Nakamura 2003; Haque et al., 2013). I In the tropics, the Tropical Rainfall Measuring Mission (TRMM) has been specifically dedicated to monitoring rainfall intensity and distribution
- ItemComparison of rainy season onset, cessation and duration for Ghana from RegCM4 and GMet Datasets(Atmospheric and Climate Sciences, 2016-04-25) Mensah, Caleb; Amekudzi, Leonard K.; Klutse, Nana Ama B.; Aryee, Jeffrey N. A.; Asare, KofiThe socio-economic sector of West African countries is rain-fed agriculture driven. Information regarding the onset, cessation and duration of the rainy season is thus, very essential. In this paper, a comparison of the onset, cessation and duration of the rainy season has been carried out using simulated rainfall data from the fourth generation Regional Climate Model (RegCM4) and rain gauge measurements from Ghana Meteorological Agency (GMet), covering a period of 1998 to 2012. Similar onset and cessation dates were seen in both the simulated and guage rainfall measurements for the various agro-ecological zones, resulting in similar duration of the rainy season. The average duration of the rainy season were less than 200 days for the savannah and coastal zones whereas the duration of the rainy season were beyond 200 days for the forest and transition zones. The bias of these comparisons was less than 30 days and the root mean square error (RMSE) values were less than 15 days for all stations, except Saltpond. The Pearson’s correlation (r) typically ranged between 0.4 and 0.8. However, negative correlations were observed for Tamale in the savannah zone, and the entire coastal zone. These findings are indications that RegCM4 has the potential to clearly simulate the movement of the rain belt, and thus, could fairly determine the onset, cessation and duration of the rainy season. The findings have significant contributions to effective water resource management and food security in Ghana, as the thriving of these sectors depend on the dynamics of the rainfall seasons.
- ItemDiversity in breeding sites and distribution of Anopheles mosquitoes in selected urban areas of southern Ghana(Parasites & Vectors, 2017) Mattah, Precious A. Dzorgbe; Futagbi, Godfred; Amekudzi, Leonard K.; Mattah, Memuna M.; Souza, Dziedzorm K. de; Kartey-Attipoe, Worlasi D.; Bimi, Langbong; Wilson, Michael D.Background: Anopheles vectors of malaria are supposedly less common in urban areas as a result of pollution, but there is increasing evidence of their adaptation to organically polluted water bodies. This study characterized the breeding habitats of Anopheles mosquitoes in the two major urban areas in southern Ghana; Accra (AMA) and Sekondi-Takoradi (STMA) Metropolitan Areas, during dry and wet seasons. Methods: Anopheles mosquito larvae were sampled using standard dipping methods to determine larval densities. The origin, nature and stability of 21 randomly selected sites were observed and recorded. Mosquito larvae were reared to adults and Anopheles species identified by both morphological and molecular means. Results: Sixty-six percent of Anopheles habitats were permanent and 34% temporal, and 74.5% man-made while 25. 5% were natural. Puddles and urban farm sites accounted for over 51% of all Anopheles mosquitoes sampled. The mean larval densities among the habitat types was highest of 13.7/dip for puddles and lowest of 2.3/dip for stream/river, and the variation between densities were significant (P = 0.002). The mean larval densities were significantly higher in the wet season than in the dry season for the two study areas combined (P = 0.0191) and AMA (P = 0.0228). Over 99% of the 5,802 morphologically identified Anopheles species were An. gambiae (s.l.) of which more than 99% of the studied 898 were An. coluzzii (62%) and An. gambiae (s.s.) (34%). Urban farms, puddles, swamps and ditches/ dugouts accounted for approximately 70% of all An. coluzzii identified. Conversely, drains, construction sites, streams/rivers and “others” contributed 80% of all An. gambiae (s.s.) sampled. The wet season had significantly higher proportion of Anopheles larvae compared to the dry season (Z = 8.3683, P < 0.0001). Also, the proportion of Anopheles mosquitoes produced by permanent breeding sites was 61.3% and that of temporary sites was 38.7%. Conclusion: Taken together, the data suggest that man-made and/ or permanent habitats were the main contributors to Anopheles larval populations in the cities and that regulation of the anthropogenic processes that lead to development of breeding places and proper environmental management can drastically reduce mosquito breeding sites in urban areas of Ghana.
- ItemEmpirical models for estimating global solar radiation over the Ashanti Region of Ghana(Journal of Solar Energy, 2014) Quansah, Emmanuel; Amekudzi, Leonard K.; Preko, Kwasi; Aryee, Jeffrey N. A.; Boakye, Osei R.; Boli, Dziewornu; Salifu, Mubarick R.Te performances of both sunshine and air temperature dependent models for the estimation of global solar radiation (GSR) over Ghana and other tropical regions were evaluated and a comparison assessment of the models was carried out using measured GSR at Owabi (6∘45�0��N, 1∘43�0��W) in the Ashanti region of Ghana. Furthermore, an empirical model which also uses sunshine hours and air temperature measurements from the study site and its environs was proposed. Te results showed that all the models could predict very well the pattern of the measured monthly daily mean GSR for the entire period of the study. However, most of the selected models overestimated the measured GSR, except in April and November, where the empirical model using air temperature measurements underestimated the measured GSR. Nevertheless, a very good agreement was found between the measured radiations and the proposed models with a coefcient of determination within the range 0.88–0.96. Te results revealed that the proposed models using sunshine hours and air temperature had the smallest values of MBE, MPE, and RMSE of −0.0102, 0.0585, and 0.0338 and −0.2973, 1.7075, and 0.9859, respectively.
- ItemMODIS NDVI trends and fractional land cover change for improved assessments of vegetation degradation in Burkina Faso, West Africa(Journal of Arid Environments, 2018-01-15) Zoungrana, Benewinde J-B.; Conrad, Christopher; Thiel, Michael; Amekudzi, Leonard K.; Dapola Da, EvaristeReduction of natural vegetation cover in the savannah of West Africa constitutes a pressing environmental concern that may lead to soil degradation. With the aim to assess the degradation of natural vegetation in the savannah of Burkina Faso, this study combined NDVI trends and fractional Land Use/Cover Change (LULCC). Fractional LULCC maps, derived from the aggregation of a 30 m Landsat LULCC map (1999–2011) to 250 m resolution of MODIS, were used to assess natural vegetation conversions in the small-scale spatial patterns of savannah landscapes. Mann-Kendall's monotonic trend test was applied to 250 m MODIS NDVI time series (2000–2011) to assess modifications of natural vegetation cover. Finally, the Spearman's correlation was employed to determine the relationship of natural vegetation degradation with environmental factors. The study revealed a vast conversion of natural vegetation into agriculture (15.9%) and non-vegetated area (1.8%) between 1999 and 2011. Significant decreasing NDVI trends (p < .05) indicated negative modifications of natural vegetation (2000–2011 period) occurring along the protected areas borders and in fragmented landscapes characterized by disruption of continuity in natural vegetation. Spearman's correlation showed that accessibility, climatic and topographic conditions favored natural vegetation degradation. The results can enable the development of efficient land degradation policies.
- ItemMosquito breeding site water temperature observations and simulations towards improved vector-borne disease models for Africa(Geospatial Health, 2016-02-18) Asare, Ernest O.; Tompkins, Adrian M.; Amekudzi, Leonard K.; Ermert, Volker; Redl, RobertAn energy budget model is developed to predict the water temperature of typical mosquito larval developmental habitats. It assumes a homogeneous mixed water column driven by empirically derived fluxes. The model shows good agreement at both hourly and daily time scales with 10-min temporal resolution observed water temperatures, monitored between June and November 2013 within a peri-urban area of Kumasi, Ghana. There was a close match between larvae development times calculated using either the model-derived or observed water temperatures. The water temperature scheme represents a significant improvement over assuming the water temperature to be equal to air temperature. The energy budget model requires observed minimum and maximum temperatures, information that is generally available from weather stations. Our results show that hourly variations in water temperature are important for the simulation of aquatic-stage development times. By contrast, we found that larval development is insensitive to sub-hourly variations. Modelling suggests that in addition to water temperature, an accurate estimation of degree-day development time is very important to correctly predict the larvae development times. The results highlight the potential of the model to predict water temperature of temporary bodies of surface water. Our study represents an important contribution towards the improvement of weather-driven dynamical disease models, including those designed for malaria early forecasting systems
- ItemMulti-Temporal Landsat Images and Ancillary Data for Land Use/Cover Change (LULCC) Detection in the Southwest of Burkina Faso, West Africa(Remote Sens., 2015-09-18) Zoungrana, Benewinde J-B.; Conrad, Christopher; Amekudzi, Leonard K.; Thiel, Michael; Dapola Da, Evariste; Forkuor, Gerald; Löw, FabianAccurate quantification of land use/cover change (LULCC) is important for efficient environmental management, especially in regions that are extremely affected by climate variability and continuous population growth such as West Africa. In this context, accurate LULC classification and statistically sound change area estimates are essential for a better understanding of LULCC processes. This study aimed at comparing mono-temporal and multi-temporal LULC classifications as well as their combination with ancillary data and to determine LULCC across the heterogeneous landscape of southwest Burkina Faso using accurate classification results. Landsat data (1999, 2006 and 2011) and ancillary data servedas input features for the random forest classifier algorithm. Five LULC classes were identified: woodland, mixed vegetation, bare surface, water and agricultural area. A reference database was established using different sources including high-resolution images, aerial photo and field data. LULCC and LULC classification accuracies, area and area uncertainty were computed based on the method of adjusted error matrices. The results revealed that multi-temporal classification significantly outperformed those solely based on mono-temporal data in the study area. However, combining mono-temporal imagery and ancillary data for LULC classification had the same accuracy level as multi-temporal classification which is an indication that this combination is an efficient alternative to multi-temporal classification in the study region, where cloud free images are rare. The LULCC map obtained had an overall accuracy of 92%. Natural vegetation loss was estimated to be 17.9% ± 2.5% between 1999 and 2011. The study area experienced an increase in agricultural area and bare surface at the expense of woodland and mixed vegetation, which attests to the ongoing deforestation. These results can serve as means of regional and global land cover products validation, as they provide a new validated data set with uncertainty estimates in heterogeneous ecosystems prone to classification errors.
- ItemNumerical simulation of surface energy and water balances over a semiarid grassland ecosystem in the West African Savanna(Advances in Meteorology, 2017) Quansah, Emmanuel; Katata, Genki; Mauder, Matthias; Annor, Thompson; Amekudzi, Leonard K.; Bliefernicht, Jan; Heinzeller, Dominikus; Balogun, Ahmed A.; Kunstmann, HaraldTo understand surface energy exchange processes over the semiarid regions in West Africa, numerical simulations of surface energy and water balances were carried out using a one-dimensional multilayer atmosphere-SOil-VEGetation (SOLVEG) model for selected days of the dry and rainy seasons over a savanna grassland ecosystem in Sumbrungu in the Upper East region of Ghana. Te measured Bowen ratio was used to partition the residual energy into the observed sensible heat flux (�) and latent heat flux (LE) in order to investigate the impact of the surface energy closure on model performance. Te results showed that the model overall reproduced the diurnal changes in the observed energy fluxes, especially the net radiation (Rn), compared to halfhourly eddy covariance flux measurements, for the study periods. Te performance measure in terms of the correlation coefcient (�), centred root mean square error (RMSE), and normalized standard deviation (�) between the simulated � and LE and their corresponding uncorrected observed values ranged between R = 0.63–0.99 and 0.83–0.94, RMSE = 0.88–1.25 and 0.88–1.92, and � = 0.95–2.23 and 0.13–2.82 for the dry and rainy periods respectively, indicating a moderate to good model performance. Te partitioning of � and LE by SOLVEG was generally in agreement with the observations during the dry period but showed clear discrepancies during the rainy period, particularly afer rainfall events. Further sensitivity tests over longer simulation periods (e.g., 1 year) are required to improve model performance and to investigate seasonal exchanges of surface energy fluxes over the West African Savanna ecosystems in more details.
- ItemAn overview of the diurnal cycle of the atmospheric boundary layer during the West African monsoon season: results from the 2016 observational campaign(Atmospheric Chemistry and Physics, 2018-03-01) Kalthof, Norbert; Lohou, Fabienne; Brooks, Barbara; Jegede, Gbenga; Adler, Bianca; Babic´, Karmen; Dione, Cheikh; Ajao, Adewale; Amekudzi, Leonard K.A ground-based field campaign was conducted in southern West Africa from mid-June to the end of July 2016 within the framework of the Dynamics–Aerosol–Chemistry– Cloud Interactions in West Africa (DACCIWA) project. It aimed to provide a high-quality comprehensive data set for process studies, in particular of interactions between lowlevel clouds (LLCs) and boundary-layer conditions. In this region missing observations are still a major issue. During the campaign, extensive remote sensing and in situ measurements were conducted at three supersites: Kumasi (Ghana), Savè (Benin) and Ile-Ife (Nigeria). Daily radiosoundings were performed at 06:00 UTC, and 15 intensive observation periods (IOPs) were performed during which additional radiosondes were launched, and remotely piloted aerial systems were operated. Extended stratiform LLCs form frequently in southern West Africa during the nighttime and persist long into the following day. They affect the radiation budget and hence the evolution of the atmospheric boundary layer and regional climate. The relevant parameters and processes governing the formation and dissolution of the LLCs are still not fully understood. This paper gives an overview of the diurnal cycles of the energy-balance components, nearsurface temperature, humidity, wind speed and direction as well as of the conditions (LLCs, low-level jet) in the boundary layer at the supersites and relates them to synoptic-scale conditions (monsoon layer, harmattan layer, African easterly jet, tropospheric stratification) in the DACCIWA operational area. The characteristics of LLCs vary considerably from day to day, including a few almost cloud-free nights. During cloudy nights we found large differences in the LLCs’ formation and dissolution times as well as in the cloud-base height. The differences exist at individual sites and also between the sites. The synoptic conditions are characterized by a monsoon layer with south-westerly winds, on average about 1.9 km deep, and easterly winds above; the depth and strength of the monsoon flow show great day-to-day variability. Within the monsoon layer, a nocturnal low-level jet forms in approximately the same layer as the LLC. Its strength and duration is highly variable from night to night. This unique data set will allow us to test some new hypotheses about the processes involved in the development of LLCs and their interaction with the boundary layer and can also be used for model evaluation
- ItemRainfall Prediction Using Machine Learning Algorithms for the Various Ecological Zones of Ghana(IEEE Access, 2022) Appiah-Badu, Nana Kofi Ahoi; Missah, Yaw Marfo; Amekudzi, Leonard K.; Najim, Ussiph; Twum, Frimpong; Ahene, Emmanuell; 0000-0002-3029-4498; 0000-0002-2186-3425; 0000-0002-2926-681X; 0000-0002-6973-7495; 0000-0002-1869-7542; 0000-0002-0810-1055Accurate rainfall prediction has become very complicated in recent times due to climate change and variability. The efficiency of classification algorithms in rainfall prediction has flourished. The study contributes to using various classification algorithms for rainfall prediction in the different ecological zones of Ghana. The classification algorithms include Decision Tree (DT), Random Forest (RF), Multilayer Perceptron (MLP), Extreme Gradient Boosting (XGB) and K-Nearest Neighbour (KNN). The dataset, consisting of various climatic attributes, was sourced from the Ghana Meteorological Agency spanning 1980 – 2019. The performance of the classification algorithms was examined based on precision, recall, f1-score, accuracy and execution time with various training and testing data ratios. On all three training and testing ratios: 70:30, 80:20 and 90:10, RF, XGB and MLP performed well, whereas KNN performed least across all zones. In terms of the execution time of the models, Decision Tree is consistently portrayed as the fastest, whereas MLP used the most run time.
- ItemRainfall Prediction Using Machine Learning Algorithms for the Various Ecological Zones of Ghana(IEEE Access, 2022-12) Appiah-Badu, Nana Kofi Ahoi; Missah, Yaw Marfo; Amekudzi, Leonard K.; Ussiph, Najim; Frimpong, Twum; Ahene, Emmanuel; 0000-0002-3029-4498; 0000-0002-2926-681X; 0000-0002-2186-3425; 0000-0002-6973-7495; 0000-0002-1869-7542; 0000-0002-0810-1055Accurate rainfall prediction has become very complicated in recent times due to climate change and variability. The efficiency of classification algorithms in rainfall prediction has flourished. The study contributes to using various classification algorithms for rainfall prediction in the different ecological zones of Ghana. The classification algorithms include Decision Tree (DT), Random Forest (RF), Multilayer Perceptron (MLP), Extreme Gradient Boosting (XGB) and K-Nearest Neighbour (KNN). The dataset, consisting of various climatic attributes, was sourced from the Ghana Meteorological Agency spanning 1980 – 2019. The performance of the classification algorithms was examined based on precision, recall, f1-score, accuracy and execution time with various training and testing data ratios. On all three training and testing ratios: 70:30, 80:20 and 90:10, RF, XGB and MLP performed well, whereas KNN performed least across all zones. In terms of the execution time of the models, Decision Tree is consistently portrayed as the fastest, whereas MLP used the most run time.
- ItemSoil and water conservation in Burkina Faso, West Africa(Sustainability, 2018-09) Nyamekye, Clement; Thiel, Michael; Schönbrodt-Stitt, Sarah; Zoungrana, Benewinde J.-B.; Amekudzi, Leonard K.Inadequate land management and agricultural activities have largely resulted in land degradation in Burkina Faso. The nationwide governmental and institutional driven implementation and adoption of soil and water conservation measures (SWCM) since the early 1960s, however, is expected to successively slow down the degradation process and to increase the agricultural output. Even though relevant measures have been taken, only a few studies have been conducted to quantify their effect, for instance, on soil erosion and environmental restoration. In addition, a comprehensive summary of initiatives, implementation strategies, and eventually region-specific requirements for adopting different SWCM is missing. The present study therefore aims to review the different SWCM in Burkina Faso and implementation programs, as well as to provide information on their effects on environmental restoration and agricultural productivity. This was achieved by considering over 143 studies focusing on Burkina Faso’s experience and research progress in areas of SWCM and soil erosion. SWCM in Burkina Faso have largely resulted in an increase in agricultural productivity and improvement in food security. Finally, this study aims at supporting the country’s informed decision-making for extending already existing SWCM and for deriving further implementation strategies.
- ItemThe Spatio-Temporal Variability of Rainfall over the Agro-Ecological Zones of Ghana(Atmospheric and Climate Sciences, 2019-07-26) Atiah, Winifred A.; Amekudzi, Leonard K.; Quansah, Emmanuel; Preko, KwasiRainfall variability plays an important role in many socio-economic activities such as food security, livelihood and farming in Ghana. Rainfall impact studies are thus very crucial for proper management of these key sectors of the country. This paper examines the seasonal and annual rainfall variability in the four agro-ecological zones of Ghana from the CHIRPS V2 rainfall time series spanning a period of 1981-2015. The rainfall indices were computed with the aid of the FClimDex package whereas the trends of these indices were further tested using the Mann Kendall trend test. The results show good agreement (r ≥ 0.7) between CHIRPS V2 and gauge in almost all portions of country although high biases were observed especially in DJF season over parts of the Northeastern (NE) portions of the country. The mean seasonal rainfall climatology over the country is observed to be in the range of 20 - 80 mm, 60 - 200 mm, 100 - 220 mm and 40 - 180 mm in DJF, MAM, JJA and SON seasons respectively with high intensities of rainfall dominating Southwestern portions of the country. The trend analysis revealed positive trends of consecutive dry days in the Transition, Forest and Coastal zones and negative trends in the Savannah zone of the country. Decreasing trends of consecutive wet days are observed over the Savannah, Transition and Coastal zones whereas increasing trends dominate the Forest zone. Savannah, Forest and Transition zones show weak increasing trends of the number of heavy rainfall days whilst weak decreasing trends are observed over the Coastal zone of the country. Similarly, weak increasing trends of the number of very heavy rainfall days are observed over all the agro-ecological zones except in the Transition zone. It is observed that the annual wet day rainfall total has increasing trend in the Savannah and Forest zones of the country whereas decreasing trends cover the remainder of the zones. The trends of these indices in the agro-ecological zones were all significant at a significant value of 0.05. This paper assessed the performance of the CHIRPS V2 rainfall data over the region and reports on the biases in seasonal rainfall amounts which are limited in previous studies. These findings have adverse impacts on rain-fed agricultural practices, water resource management and food security over the country.
- ItemValidation of TRMM and FEWS Satellite Rainfall Estimates with Rain Gauge Measurement over Ashanti Region, Ghana(Atmospheric and Climate Sciences, 2016-10-28) Amekudzi, Leonard K.; Osei, Marian A.; Atiah, Winifred A.; Aryee, Jeffrey N. A.; Ahiataku, Maureen A.; Quansah, Emmanuel; Preko, Kwasi; Danuor, Sylvester K.; Fink, Andreas H.Satellite rainfall estimates have predominantly been used for climate impact studies due to poor rain gauge network in sub-Saharan Africa. However, there are limited microscale studies within the sub-region that have assessed the performance of these satellite products, which is the focus of the present study. This paper therefore considers validation of Tropical Rainfall Measuring Mission (TRMM) and Famine Early Warning System (FEWS) satellite estimates with rain gauge measurements over Ashanti region of Ghana. First, a consistency assessment of the two gauge data products, the Automatic Rain Gauge (ARG) and Ghana Meteorological Agency (GMet) Standard Rain Gauge (SRG) measurements, was performed. This showed a very good agreement with correlation coefficient of 0.99. Secondly, satellite rainfall products from TRMM and FEWS were validated with the two gauge measurements. Validation results showed good agreement with correlation coefficients of 0.6 and 0.7 for TRMM and FEWS with SRG, and 0.87 and 0.86 for TRMM and FEWS with ARG respectively. Probability Of Detection (POD) and Volumetric Hit Index (VHI) were found to be greater than 0.9. Volumetric Critical Success Index (VCSI) was 0.9 and 0.8 for TRMM and FEWS respectively with low False Alarm Ratio (FAR) and insignificant Volumetric Miss Index (VMI). In general, relatively low biases and RMSE values were observed. The biases were less than 1.3 and 0.8 for TRMM and FEWSRFE respectively. These indicate high rainfall detection capabilities of both satellite products. In addition, both TRMM and FEWS were able to capture the onset, peak and cessation of the rainy season, as well as the dry spells. Although TRMM and FEWS sometimes under/overestimated rainfall, they have the potential to be used for agricultural and other hydro-climatic impact studies over the region. The Dynamic Aerosol-Cloud-Chemistry Interactions in West Africa (DACCIWA) project will provide an improved spatial gauge network database over the study area to enhance future validation and other climate impact studies.
- ItemVariabilities in Rainfall Onset, Cessation and Length of Rainy Season for the Various Agro-Ecological Zones of Ghana(Climate, 2015-06-15) Amekudzi, Leonard K.; Yamba, Edmund I.; Preko, Kwasi; Asare, Ernest O.; Aryee, Jeffrey; Baidu, Michael; Codjoe, Samuel N. A.This paper examines the onset and cessation dates of the rainy season over Ghana using rain gauge data from the Ghana Meteorological Agency (GMet) over the period of 1970–2012. The onset and cessation dates were determined from cumulative curves using the number of rainy days and rainfall amount. In addition, the inter-annual variability of the onset and cessation dates for each climatic zone was assessed using wavelet analysis. A clear distinction between the rainfall characteristics and the length of the rainy season in the various climatic zones is discussed. The forest and coastal zones in the south had their rainfall onset from the second and third dekads of March. The onset dates of the transition zone were from the second dekad of March to the third dekad of April. Late onset, which starts from the second dekad of April to the first dekad of May, was associated with the savannah zone. The rainfall cessation dates in the forest zone were in the third dekad of October to the first dekad of November, and the length of the rainy season was within 225–240 days. The cessation dates of the coastal zone were within the second and third dekad of October, and the length of rainy season was within 210–220 days. Furthermore, the transition zone had cessation dates in the second to third dekad of October, and the length of the rainy season was within 170–225 days. Lastly, the savannah zone had cessation dates within the third dekad of September to the first dekad of October, and the length of rainy season was within 140–180 days. The bias in the rainfall onset, cessation and length of the rainy season was less than 10 days across the entire country, and the root mean square error (RMSE) was in the range of 5–25 days. These findings demonstrate that the onset derived from the cumulative rainfall amount and the rainy days are in consistent agreement. The wavelet power spectrum and its significant peaks showed evidence of variability in the rainfall onset and cessation dates across the country. The coastal and forest zones showed 2–8- and 2–4-year band variability in the onsets and cessations, whereas the onset and cessation variability of the transition and savannah zones were within 2–4 and 4–8 years. This result has adverse effects on rain-fed agricultural practices, disease control, water resource management, socio-economic activities and food security in Ghana.