Dar es Salaam, like other cities in Africa, experiences flash floods during the rainfall season that destroy infrastructure due to the overflow of rivers and blocked sewage. This study investigates the historical and future variability and changes in spatial and temporal rainfall over Dar es Salaam. Station data and Climate Hazards Group Infrared Precipitation with Stations (CHIRPS) gridded data crossing 38 years (1982–2019) were used as a baseline and the Coordinated Regional Climate Downscaling Experiment (CORDEX) dataset from 2021 to 2050 was used for projection under Representative Concentration Pathway (RCP 4.5) forcing scenarios. A trend analysis of historical data was conducted at monthly, seasonal, and annual timescales. Mann–Kendall statistical tests and Sen’s slope estimator were applied to identify the current trend direction and magnitude of changes in rainfall patterns over time. A standardized anomaly index (SAI) was also employed to detect the region’s trends in wetness and dryness. The spatial distribution of rainfall in the city was investigated using an inverse distance weighted (IDW) interpolation technique. The statistical results reveal that a non-significant trend in rainfall was observed on monthly, seasonal, and annual timescales. Generally, in the future (2021–2050), the annual cycle of rainfall shows a slight decrease in monthly rainfall, especially from January to August, and an increase from September to December compared to historical (1982–2019) rainfall, for most of studied locations. Spatially, the distribution of projected rainfall shows that the southern part of the city will experience higher rainfall than other parts. The most significant findings were a decrease in annual projected rainfall by 20%, the MAM projected rainfall season increased by 42%, and an increase of 38% of the OND-projected rainfall season. The findings of this study will be useful for the improved management and planning of the city.

A gabion stepped weir is a permeable weir that consists of a gabion box filled with stone aggregates. It is cost-effective structure used for the dissipation of water flow energy from upstream to downstream. Gabion weir also allows the movement of aquatic life and transportation of physical and chemical substances present in water. In this study, energy dissipation in terms of inverse relative energy dissipation (IRED) over gabion stepped weir has been studied. It was observed that the existing predictor does not give a reasonable estimate for IRED. Therefore, the data have been reanalysed to develop a generalized regression equation for IRED. Generalized models using Gene Expression Programming (GEP) and Group Method of Data Handling (GMDH) were also developed. The predictions based on GMDH model (R = 0.979, E = 0.96 and RMSE = 0.314) were found more satisfactory than those given by traditional regression equations (R = 0.929, E = 0.91 and RMSE = 0.557) as well as those given by the GEP model (R = 0.959, E = 0.94 and RMSE = 0.476). Sensitivity analysis shows that the Froude number before the jump is the most important parameter for the prediction of IRED.

The vulnerability of soil toward erosion might be reduced by having a good vegetative cover over the soil surface, slope improvement, and improving soil properties so that it is not easily detached and transported. However, the establishment of proper vegetative cover is a long process because it takes time for seeds to germinate and attain maturity. As an alternative approach, if soil resistance was increased by increasing the shear strength of soil against erosive forces offered by eroding agents, the soil system would become capable of withstanding the detachment of its particles on the application of shear stress. To achieve the desired strength, jute fiber and guar gum were added (0.3%, 0.5%, and 0.7%) to a test plot of 1 m² area which resulted in three different trays of three different strengths. The strength parameters were determined with the help of a triaxial test where unconsolidated undrained (UU) conditions were maintained throughout the experiment. The tray was maintained at different slopes (4%, 6%, 8%, 10%, and 12%) under a rainfall simulator of 1 m² area that was capable of producing rainfall intensity of 12.8 and 17.5 cm/h. The sediment outflow for a particular tray at different rainfall intensity and the slope were collected and measured. The recorded observations revealed that the value of the shear strength of soil increased as a result of the applied treatments and the soil loss rate/sediment outflow rate decreased for every combination of land slope and rainfall intensity. In addition, it was found that for a particular value of cohesion and angle of internal friction, the runoff rate increased with rainfall intensity for every land slope and the sediment concentration and sediment outflow rate increased with rainfall intensity as well as land slope. The results of this study will be useful for measuring soil loss, sediment runoff, and sediment discharged from farmland taking into account the properties of rainfall, soil, and flow.

Understanding the hydrochemical composition of water resources in the Ngorongoro Conservation Area (NCA, Dodoma, Tanzania) related to climate variability is essential for sustainable development. Thus, the current study used the HYDRUS-1D model to assess the groundwater quality change due to the leaching of hydrochemicals from surface water under the climate variability of the NCA. This study observed that the area’s surface water had varying hydrochemical contaminants, whereas the groundwater is currently most suitable for drinking and domestic purposes. However, it is predicted that two anions (${\mathrm{Cl}}^{-1}$ and $\mathrm{PO}{4}^{-3}$ ) and two cations (${\mathrm{Na}}^{+}$ and ${\mathrm{K}}^{+}$ ) are expected to exceed the permissible limits from 2036 to 2050, considering the anticipated climatic conditions. Changes in groundwater quality for cations and anions are significantly correlated to evapotranspiration and temperature, with Pearson’s coefficient of determinations $r$ between 0.35 and 0.66. The findings of this study are necessary to benchmark better water resources management planning. Understanding the hydrochemical composition of water resources in the Ngorongoro Conservation Area (NCA, Dodoma, Tanzania) related to climate variability is essential for sustainable development. Thus, the current study used the HYDRUS-1D model to assess the groundwater quality change due to the leaching of hydrochemicals from surface water under the climate variability of the NCA. The hydrochemical assessment results for the composition of major cations and anions to the subsurface indicate the significant influence of future changes in the climate of the study area. The results indicate, two cations (${\mathrm{Na}}^{+}$ and ${\mathrm{K}}^{+}$ ) and two anions (${\mathrm{Cl}}^{-1}$ and ${\mathrm{PO}}_4^{-}$ ) would exceed the World Health Organization (WHO) and Tanzania Bureau of Standards (TBS) permissible limits between 2036 and 2050. Statistically, changes in groundwater quality for both cations and anions are significantly correlated with evapotranspiration and temperature. Therefore, apart from other factors such as volcanic activities and accelerated human interventions that could affect water quality, climate change can be considered the main driver for hydrochemical movements to the groundwater. Hence, a detailed climate change study should be conducted to precisely inform the impacts of future changes in climate parameters on water quality deterioration. The findings from such studies can be used for sustainable management of the water resources in this area.