Lamek Nahayo

USLE-Based Assessment of Soil Erosion by Water in the Nyabarongo River Catchment, Rwanda

Soil erosion has become a serious problem in recent decades due to unhalted trends of unsustainable land use practices. Assessment of soil erosion is a prominent tool in planning and conservation of soil and water resource ecosystems. The Universal Soil Loss Equation (USLE) was applied to Nyabarongo River Catchment that drains about 8413.75 km2 (33%) of the total Rwanda coverage and a small part of the Southern Uganda (about 64.50 km2) using Geographic Information Systems (GIS) and Remote Sensing technologies. The estimated total annual actual soil loss was approximately estimated at 409 million tons with a mean erosion rate of 490 t·ha−1·y−1 (i.e., 32.67 mm·y−1). The cropland that occupied 74.85% of the total catchment presented a mean erosion rate of 618 t·ha−1·y−1 (i.e., 41.20 mm·y−1) and was responsible for 95.8% of total annual soil loss. Emergency soil erosion control is required with a priority accorded to cropland area of 173,244 ha, which is extremely exposed to actual soil erosion rate of 2222 t·ha−1·y−1 (i.e., 148.13 mm·y−1) and contributed to 96.2% of the total extreme soil loss in the catchment. According to this study, terracing cultivation method could reduce the current erosion rate in cropland areas by about 78%. Therefore, the present study suggests the catchment management by constructing check dams, terracing, agroforestry and reforestation of highly exposed areas as suitable measures for erosion and water pollution control within the Nyabarongo River Catchment and in other regions facing the same problems.

Agricultural impact on environment and counter measures in Rwanda

Rapid intensive agriculture often generates serious environmental concerns including soil erosion, water pollution and greenhouses gases. This paper assesses the impact of agriculture and its practices on environment in Rwanda from 1990 to 2012. Data provided by the World Bank were analyzed with Origin Pro 9 for statistical analysis. Also, a review on physical-chemical parameters and heavy metals of water resources home to or surrounded by cultivated mountains was adopted in this study. The results showed that agricultural records decreased from 1990 to 1994. However, after then, the short season cropland like cereals increased from 7.04 to 17.45%; roots and tubers increased from 13.17 to 21.69% in 1995 and 2012, respectively, whilst permanent cropland remained constant at 10.13%. As Rwandan soil is almost steep slope, this heavily exposes the soil to erosion, fertility loss and landslides as permanent crops to enhance fertility and erosion control are decreasing. Also, fertilizers increased from 2,149 to 27,748 tons, irrigation spaced from 4,000 to 10,000 ha which can be the reasons of rise of agricultural emissions. The reviewed studies estimated high concentration of the total nitrogen, total suspended solids, manganese, lead and iron exceeding the standards of the European Union and World Health Organization. From the above findings, it is suggested to regularly monitor water quality and promote its purification measures, to fertilize and irrigate timely and appropriately, expand areas under agroforestry and permanent crops, promote bench terraces practices for durable soil erosion control and water quality in Rwanda. Key words: Agriculture, environment, Rwanda, soil erosion, water pollution.

Early alert and community involvement: approach for disaster risk reduction in Rwanda

Natural disasters’ socioeconomic and environmental losses are predicted to rise, unless early warning, full stakeholders and community involvement in the mitigation, adaptation and risk reduction are squarely engaged. The objective of this study is to assess the impact of early alert and community involvement in disaster risk reduction in Nyabihu District, Western Rwanda. A quota sampling method was employed to obtain a sample of 240 households from 12 sectors of Nyabihu District in 2015. A structured questionnaire was used, and the field data collected were computed by using SPSS16.0 for Windows. The results indicated that, as stated by respondents, the frequently experienced disasters are floods (51.25%) and landslides (42.08%). However, as asserted by 68% of informants, disaster-related information is communicated through radio channels after the occurrence, while 29% of them declared that disaster information is disseminated before occurrence, which implies the rising level of risk vulnerability and incidences to the community due to lack of early warning. A lower community participation in disaster risk preparedness and mitigation was noticed (6.2%) while 31.6% mentioned taking part in activities aimed at coping with the aftermath (adaptation). Moreover, disaster risk reduction government policies are preferentially implemented (42.9%) other than considering the community’s knowledge (14.1%). To halt the gradual increase in disasters’ associated risks and losses, it is suggested to introduce disaster-related training across the community, introduce disaster courses from elementary schools and integrate the community in decision-making process.

Landslide Susceptibility Assessment Using Spatial Multi-Criteria Evaluation Model in Rwanda

Landslides susceptibility assessment has to be conducted to identify prone areas and guide risk management. Landslides in Rwanda are very deadly disasters. The current research aimed to conduct landslide susceptibility assessment by applying Spatial Multi-Criteria Evaluation Model with eight layers of causal factors including: slope, distance to roads, lithology, precipitation, soil texture, soil depth, altitude and land cover. In total, 980 past landslide locations were mapped. The relationship between landslide factors and inventory map was calculated using the Spatial Multi-Criteria Evaluation. The results revealed that susceptibility is spatially distributed countrywide with 42.3% of the region classified from moderate to very high susceptibility, and this is inhabited by 49.3% of the total population. In addition, Provinces with high to very high susceptibility are West, North and South (40.4%, 22.8% and 21.5%, respectively). Subsequently, the Eastern Province becomes the peak under low susceptibility category (87.8%) with no very high susceptibility (0%). Based on these findings, the employed model produced accurate and reliable outcome in terms of susceptibility, since 49.5% of past landslides fell within the very high susceptibility category, which confirms the model’s performance. The outcomes of this study will be useful for future initiatives related to landslide risk reduction and management.