Temperature variability and long-term warming are increasingly threatening agricultural sustainability in southern Rwanda, where smallholder farmers rely on climate-sensitive crops. However, comprehensive spatiotemporal assessments of temperature extremes and their impacts on agriculture remain limited. This study used daily minimum and maximum temperature data from 1983 to 2021 for Huye District, provided by the Rwanda Meteorology Agency, and crop productivity data for rice and beans from 2017 to 2021 obtained from the National Institute of Statistics of Rwanda. The study analysed spatial and seasonal variability and trends of minimum temperature (Tmin), maximum temperature (Tmax), mean temperature (Tmean), and extreme temperature indices, including coldest nights (TNn), warm nights (TN90p), hottest days (TXx), and diurnal temperature range (DTR) across 14 administrative sectors within the district. Variability was assessed using the coefficient of variation, trends using the Modified Mann–Kendall test and Sen’s slope estimator, and temperature crop relationships using Pearson correlation and linear regression. Results revealed strong spatial and seasonal variability, with Tmin variability of 7.92–8.92
In highland regions, such as Nyaruguru District of Rwanda, temperature varies over short distances due to complex topography, creating distinct microclimates that strongly influence crop growth, development, and yield performance. However, no study has analysed temperature variability and trends at a microclimateinformed zonal scale in Nyaruguru District, despite its critical importance for accurate agricultural planning and climate-resilient decision-making. This study addresses this gap by delineating the district into four nearhomogeneous climate zones using K-means clustering and analysing spatiotemporal temperature variability and trends from 1983 to 2021 at these climate zones. Daily gridded minimum (Tmin) and maximum (Tmax) temperature data from 73 grid points in Nyaruguru obtained from Rwanda Meteorology Agency were used. Temperature variability was assessed using the Coefficient of Variation, while trends were detected using the Modified Mann-Kendall test (MMK), Sen's slope estimator and Innovative Trend Analysis (ITA) at zonal, seasonal (January-February, March-May, June-August, and September-December) and annual scales. The effects of temperature variability on crops were evaluated using the Spearman correlation coefficient with staple crop yields. Results revealed clear spatial heterogeneity, with moderate to low variability occurred in Tmin (14.9-17.2%) and Tmean (7.1-8.2%) during January-February, especially in Zone 2. Significant warming trends were observed in Tmin (0.35-0.43 degrees C/decade) and Tmean (0.43-0.48 degrees C/decade) at the 99% confidence level using MMK while ITA showed strong increasing Tmin, Tmean and Tmax trends in zone 3. Tmean variability was negatively correlated with Irish potato and cassava yields. These findings highlight the importance of microclimate-based analysis for climate-smart agricultural planning to improve crop productivity in highland regions.
This study investigates the seasonal dynamics, source apportionment, and human health risks of toxic metals in harvested rainwater (HRW) using a geochemical and statistical approach. Monthly samples were collected from April to August to capture wet-season variations. Results show significantly elevated metal concentrations at the onset of the rainy season, particularly for Cd (3.30 mg/L), Pb (3.02 mg/L), and As (0.30 mg/L), reflecting the “first-flush” effect. Concentrations declined over time, indicating wash-off of accumulated atmospheric and rooftop contaminants. Geoaccumulation index (Igeo) and enrichment factor (EF) analyses reveal Cd and Se as the most critical pollutants, with Igeo > 3 and EF > 5000, pointing to strong anthropogenic sources. Health risk assessment indicates severe non-carcinogenic risks, especially for children, with hazard quotients (HQ) exceeding safe limits (HQ > 1) for Cd (HQ = 21.83) and Pb (HQ = 32.53). Arsenic and Se also contribute significantly to health risks. Binary elemental ratios (e.g., Ca/Mg, Na/K) support source differentiation between natural and anthropogenic inputs. The findings highlight that HRW, despite its utility, poses serious health risks without treatment. Mitigation strategies such as first-flush diversion, improved roofing materials, and regular maintenance are essential for safe utilization. This work supports SDG 6 by promoting safe water practices in vulnerable communities.
Black carbon (BC) is a major urban pollutant affecting climate and health. This review examines studies published between 2018 and 2026 on BC sources, mixing state, and impacts. Traffic emissions dominate developed cities, while biomass and residential combustion are major sources in developing regions. Particle mixing influences radiative forcing and respiratory deposition. Standardized measurements and integrated climate-health assessments are needed.
Rapid urbanisation in Kigali has intensified pressures on land, water resources and drainage infrastructure, replacing natural vegetation with impervious surfaces. The transformation has escalated the frequency of urban flooding, necessitating a spatial evaluation of the link between urban development and stormwater dynamics to prevent future hazards. This study examines the extent of urbanisation in Kigali and its influence on stormwater runoff. Specifically, the research aimed to map LULC changes between 2013 and 2023, estimate stormwater vulnerability using the SCS-CN method. The research applied a mixed-method approach by integrating GIS-based hydrological modelling (Rational Method and SCS-CN). Runoff volumes were estimated using both the Rational Method and the SCS-CN approach, integrating rainfall data, hydrological soil group classifications and LULC layers to quantify the impact of expanding impervious surfaces. Data from Meteo Rwanda, satellite images for LULC, Hydrological soil data and Kigali administrative shapefiles supported spatial analyses and vulnerability mapping. The result indicates a significant expansion in built-up areas from covering 25.3% of the city in 2013 to 32.6% in 2023, which directly correlates with an increase in surface runoff volumes. The hydrological analysis revealed that dense urban zones, situated on Hydrologic Soil Group D, show high Curve Numbers (CN 90–98), which indicate very low infiltration rates and severe flood vulnerability. It also revealed that runoff volume have increased due to the expansion of impervious surface. These findings demonstrate that continued urban expansion without adequate stormwater controls increases flood vulnerability across Kigali. Kigali City authorities should strongly enforce urban planning regulations that limit impervious surfaces in high-vulnerability zones and adopt nature-based and stormwater management techniques such as green infrastructure, permeable pavements and rainwater harvesting.
