Spatial and temporal rainfall variability impacts on faecal sludge management services in Sinza River Catchment at Tandale Ward in Dar es Salaam, Tanzania

Poor faecal sludge management in urban informal settlements poses significant public health risks, particularly in flood-prone areas. This study addresses the critical knowledge gap in understanding how rainfall variability affects faecal sludge management services (FSMs) in the densely populated Sinza River catchment in Dar es Salaam Tanzania. The methodology employed was the Standardized Anomaly Index (SAI), Coefficient of Variance (CV), and Precipitation Concentration Index (PCI) - the Mann–Kendall (MK) trend test and Sen’s slope (SS), while spatial distribution was measured by Inverse Distance Weighting (IDW) interpolation in GIS. The key findings revealed (1) seasonal rainfall variability exceeding annual rainfall variations, (2) The wettest year, was 2019, which recorded a maximum SAI of 3.14 and 3.15 at Msimbazi and Ubungo stations, and the year 2003 was the driest with SAI of −2.03. Annual and seasonal PCI analysis indicated moderate to irregular rainfall distribution, except for the dry season at Msimbazi station with PCI > 20. The MK and SS, indicate a negative trend of −1.39. These findings have direct applications for FSM infrastructure planning in Tandale and in other areas with the same characteristics. Study limitations include the absence of continuous FSM service data and the need for more detailed hydraulic modeling of the catchment area.