The Influence of Climate Change and Variability on Spatio -Temporal Rainfall and Temperature Distribution in Zanzibar

Climate change has resulted in serious social-economic ramifications and extremely catastrophic weather events in the world, Tanzania and Zanzibar in particular. Adaptation is the only option to reduce those impacts. This study mainly focuses on the influence of climate change and variability on spatio - temporal rainfall and temperature distribution in Zanzibar. The study used station observation datasets of rainfall, maximum an minimum temperature (Tmax) and (Tmin) which were acquired from Tanzania Meteorological Authority (TMA), and the Coordinated Regional Climate Downscaling Experiment program (CORDEX) projected datasets, from the Regional climate model HIRHAM5 developed by the Danish Meteorological Institute (DMI) under Driving model ICHEC-EC- EARH with used realization r3i1P1 in the region AFR-44; for the periods of 1991-2020 used as a baseline or historical (HS), 2021-2050 as near future (NF) and 2051-2080 as far future(FF), under two representative concentration pathways (RCP) of 4.5 and 8.5, respectively. The long-term observed Tmax and Tmin were used to produce time series for observing the nature and trends of the used climate parameters, while the observed rainfall data was used for understanding the wet and dry periods, as well as rainfall trend and slope (at p ≤ 0.05) using the Standardized Precipitation Index (SPI) and the Mann Kendall test (MK). Moreover, the study used the Inverse Distance Weighting (IDW) interpolation techniques for the three decades of 1991-2000 used as D1, 2001-2010 as D2 and 2011-2020 as D3 to analyze spatial rainfall distribution in Zanzibar. As for the projected datasets the Climate Data Operator Commands (CDO), the python scripts and Grid analysis and Display System (GrADS) softwares were used to process and display the projected datasets of rainfall, Tmax and Tmin for the HS, NF and FF, respectively. The study results show that the observed Tmax increased by the rates of 0.035yr-1 and 0.0169˚Cyr-1 , while the Tmin was increased by a rate of 0.064˚Cyr-1 and 0.104 ˚Cyr-1 for Unguja and Pemba, respectively. The temporal distribution of wetness and dryness indices showed a climate shift from near normal to moderate wet during 2005 at Zanzibar Airport, while normal to moderately dry conditions, were observed at Matangatuani in Pemba indicating both wet and dry conditions. The decadal rainfall distributions revealed higher rainfall intensity with an increasing trend and good spatial distribution in D3 during March to May (MAM) and October to December (OND). The projected results for Tmax during MAM and OND depicted higher values ranging from 1.7 - 1.8 ℃ to 1.9 - 2.0 ℃ and 1.5 to 2.0 ℃ in FF compared to NF under both RCPs. Also, higher Tmin values of 1.12 - 1.16℃ was projected in FF for MAM and OND under both RCPs. Besides, the rainfall projection generally revealed increased rainfall intensity in the range of 0 - 25 mm for Pemba and declined rainfall in the range of 25 - 50 mm in Unguja under both RCPs in the perspectives of both NF and FF. Conclusively the study has shown that the undergoing climate change has posed a significant impact on both rainfall and temperature spatial and temporal distribution in Zanzibar (Unguja and Pemba), with Unguja being projected to have higher rainfall deficits while increasing rainfall strengths in Pemba. Thus, the study calls for more climate change studies using multi-model ensemble CORDEX or CIMIP6 datasets for more improvement results and formulation of effective adaptation, strategies and resilience mechanisms to combat the projected climate change impacts especially in the agricultural sector, water and food security.
This study mainly focuses on the influence of climate change and variability on spatio - temporal rainfall and temperature distribution in Zanzibar.