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Correlation of Rainfall Anomalies in Rwanda from September to December (SOND) with Indian Ocean Dipole (IOD) and El Nino Southern Oscillation (ENSO) Events

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Journal of Geoscience and Environment Protection 2024年第6期12卷 115-134页

作者： Frank Rusanganwa Ling Zhang Jonah Kazora Joseph Ndakize Sebaziga samuel ekwacu College of Atmospheric Science Nanjing University of Information Science and Technology Nanjing China Rwanda Meteorology Agency (Meteo-Rwanda) Kigali Rwanda School of Science and Technology University of Rwanda Kigali Rwanda Uganda National Meteorological Authority (UNMA) Kampala Uganda

Understanding the relationship between rainfall anomalies and large-scale systems is critical for driving adaptation and mitigation strategies in socioeconomic sectors. This study therefore aims primarily to investigate the correlation between rainfall anomalies in Rwanda during the months of September to December (SOND) with the occurrences of Indian Ocean Dipole (IOD) and El Nino Southern Oscillation (ENSO) events. The study is useful for early warning and forecasting of negative effects associated with extreme rainfall anomalies across the country, using Climate Hazards Group InfraRed Precipitation with Station (CHIRPS), the National Centers for Environmental Prediction (NCEP) National Center for Atmospheric Research (NCAR) reanalysis sea surface temperature and ERA5 reanalysis datasets, during the period of 1983-2021. Both empirical orthogonal function (EOF), correlation analysis and composite analysis were used to delineate variability, relationship and the related atmospheric circulation between Rwanda seasonal rainfall September to December (SOND) with Indian Ocean Dipole (IOD) and El-Nino Southern Oscillation (ENSO). The results for Empirical Orthogonal Function (EOF) for the reconstructed rainfall data set showed three modes. EOF-1, EOF-2 and EOF-3 with their total variance of 63.6%, 16.5% and 4.8%, Indian ocean dipole (IOD) events resulted to a strong positive correlation of rainfall anomalies and Dipole model index (DMI) (r = 0.42, p value = 0.001, DF = 37) significant at 95% confidence level. The composite analysis for the reanalysis dataset was carried out to show the circulation patterns during four different events correlated with September to December seasonal rainfall in Rwanda using T-test at 95% confidence level. Wind anomaly revealed that there was a convergence of south westerly winds and easterly wind over the study area during positive Indian Ocean Diploe (PIOD) and PIOD with El Nino concurrence event years. The finding of this study will cont

关键词： Correlation Rainfall Anomalies Rwanda Indian Ocean Dipole El Nino Southern Oscillation

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Potential Driving Systems Associated with Extreme Rainfall across East Africa during October to December (OND) Season 2019

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Journal of Geoscience and Environment Protection 2024年第7期12卷 25-49页

作者： Constantine Ingeri Wang Wen Joseph Ndakize Sebaziga Vedaste Iyakaremye samuel ekwacu Prosper Ayabagabo Anthony Twahirwa Jonah Kazora School of Atmospheric Sciences Nanjing University of Information Science and Technology Nanjing China Rwanda Meteorology Agency (Meteo Rwanda) Kigali Rwanda School of Science and Technology University of Rwanda (UR-CST) Kigali Rwanda Climate and Clean Air Coalition Secretariat Paris France Rwanda Environment Management Authority (REMA) Kigali Rwanda Uganda National Meteorological Authority (UNMA) Kampala Uganda Department of Earth and Climate Science University of Nairobi Nairobi Kenya

The East African (EA) region highly experiences intra-seasonal and inter-annual variation in rainfall amounts. This study investigates the driving factors for anomalous rainfall events observed during the season of October-November-December (OND) 2019 over the region. The study utilized daily rainfall data from Climate Hazards Group InfraRed Precipitation with Station Data Version 2 (CHIRPSv2) and the driving systems data. Statistical spatiotemporal analysis, correlation, and composite techniques were performed to investigate the teleconnection between OND 2019 seasonal rainfall and global synoptic climate systems. The findings showed that the OND 2019 experienced seasonal rainfall that was twice or greater than its seasonal climatology and varied with location. Further, the OND 2019 rainfall showed a positive correlation with the Indian Ocean Dipole (IOD) (0.81), Nino 3 (0.51), Nino 3.4 (0.47), Nino 4 (0.40), Pacific Decadal Oscillation (PDO) (0.22), and North Tropical Atlantic (NTA) (0.02), while El Nino-Southern Oscillation (ENSO) showed a negative correlation (−0.30). The region was dominated by southeasterly warming and humid winds that originated from the Indian Ocean, while the geopotential height, vertical velocity, and vorticity anomalies were closely related to the anomalous rainfall characteristics. The study deduced that the IOD was the major synoptic system that influenced maximum rainfall during the peak season of OND 2019. This study therefore provided insights on the diagnosis study of OND 2019 anomalous rainfall and its attribution over the EA. The findings of the study will contribute to improvements in forecasting seasonal rainfall by regional climate centers and national meteorological centers within the region.

关键词： East Africa Driving Climate Systems October-November-December (OND) 2019 Rainfall

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Analysis of Changes of Extreme Temperature during June to August Season over Tanzania

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Journal of Geoscience and Environment Protection 2024年第2期12卷 44-56页

作者： Justus Renatus Mbawala Huixin Li Jiani Zeng Daudi Mikidadi Ndabagenga Anqin Tan Daniela Janine Beukes Praksed Mrosso Rafael samuel ekwacu Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters/Key Laboratory of Meteorological Disaster Ministry of Education/School of Atmospheric Sciences Nanjing University of Information Science and Technology Nanjing China National Meteorological Training Centre Kigoma Tanzania Tanzania Meteorological Authority (TMA) Forecasting Office Kilimanjaro International Airport (KIA) Kilimanjaro Tanzania Namibia Meteorological Service Windhoek Namibia Uganda National Meteorological Authority Kampala Uganda

Natural and human systems are exposed and vulnerable to climate extremes, which contributes to the repercussions of climate variability and the probability of disasters. The impacts of both natural and human-caused climate variability are reflected in the reported changes in climate extremes. Particularly at the local community levels in the majority of the regions, there is currently a dearth of information regarding the distribution, dynamics, and trends of excessive temperatures among the majority of Tanzanians. Over the years 1982-2022, this study examined trends in Tanzania’s extreme temperature over the June to August season. Based on the distinction between absolute and percentile extreme temperatures, a total of eight ETCCDI climate indices were chosen. Mann-Kendall test was used to assess the presence of trends in extreme climatic indices and the Sen’s Slope was applied to compute the extent of the trends in temperature extremes. The study showed that in most regions, there is significant increase of warm days and nights while the significant decrease of cold days and nights was evident to most areas. Moreover, nighttime warming surpasses daytime warming in the study area. The study suggests that anthropogenic influences may contribute to the warming trend observed in extreme daily minimum and maximum temperatures globally, with Tanzania potentially affected, as indicated in the current research. The overall results of this study reflect patterns observed in various regions worldwide, where warm days and nights are on the rise while cold days and nights are diminishing.

关键词： Indices Warm Days and Nights Cold Days and Nights ECA&D Tanzania

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