Abstract
Spatial and temporal rainfall trends over the Tanzanian coast are analysed and trends for over 50 years are investigated. This type of study is crucial at this time because the area under study is now one of the world’s economic hotspots, as major gas fields have been discovered and the area also has high potential for oil field discoveries. Methods applied in this study include the Mann-Kendall test for rainfall data to detect the long-term trends, while Sen’s slope estimator test was used for finding the magnitude of change over time. The results exhibited rainfall trend patterns with substantial variations between the stations. The Z value of the Mann-Kendall test showed various months with negative trend at a significance level ≥95%. The few months that showed a positive trend were not statistically significant. Generally, rainfall trends varied in different months for different stations. However, the most outstanding observation on individual months is July, which showed a highly statistically significant (99.9%) reduction in rainfall for the whole coastal area, including the regions of Mtwara, Dar es Salaam and Tanga. The last part of this paper describes the relationship between July rainfall and the horizontal winds from the National Centre for Environmental Prediction/National Centre for Atmospheric Research (NCEP/NCAR) re-analysis. It is observed that the strength of the anticyclonic flow over the southwest Indian Ocean, which is associated with the westward fluxes of moisture, is responsible for rainfall over the whole coastal area of Tanzania during July.
Highlights
In this study, more than 50 years of rainfall data are considered in an effort to determine spatio-temporal trends in Tanzania’s coastal rainfall
Tanzania is projecting itself to become a middle-income economy by 2025, and this comes with improvements and growth in industries, manufacturing, consumer goods and agriculture
Tanga and Dar es Salaam are found in a bimodal rainfall zone, with ‘long’ rains centred on March to May (MAM) known in Tanzania as Masika rains, and ‘short’ rains in October to December (OND) known as Vuli rains [2,19]
Summary
More than 50 years of rainfall data are considered in an effort to determine spatio-temporal trends in Tanzania’s coastal rainfall This type of study is crucial at this time because the area under study is an area of significant activities (hotspot) globally, as major gas fields have been discovered and the area has potential for oil field discoveries. Dar es Salaam in the central coast (8%) and Tanga in the north (1%) [3] This sector is troubled by rainfall variability and climate uncertainty will increase with the hydrocarbon discoveries. Tanzania is projecting itself to become a middle-income economy by 2025, and this comes with improvements and growth in industries, manufacturing, consumer goods and agriculture These developments will form part of a global trend towards increasing the energy in the atmosphere and altering the climate of the area that includes the area rainfall. This study analyses rainfall time series data at a monthly scale over the Tanzania Coast from the 1950s to 2011, in order to detect potential trends and assess their significance
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