Resumo. Abstract: Aim Estimate the input of loads of N and P emitted by natural (atmospheric deposition and soil denudation) and anthropogenic (agriculture, livestock and sewage) factors for the hydrographic basins of two reservoirs in the Brazilian semiarid region (Mendubim and Umari). Methods In the present work, we use georeferenced data provided by official agencies, data presented in academic papers, field samples and laboratory analysis of emission factors in the estimates of nitrogen and phosphorus inputs in reservoir basins of Brazilian semiarid region. Results Soil denudation was identified as the main natural source of N and atmospheric deposition as the main source of P in both basins. Among the anthropogenic sources, the main source of N and P, for the two basins, was livestock. The total loads (natural and anthropogenic) of N (579.01 tonne. year-1) and P (136.35 tonne. year-1) received by the Umari basin was, respectively, 43.90% and 22.10% higher than those received by Mendubim, with a predominance of anthropogenic sources in both nitrogen and phosphorus emission. Conclusions The results showed the importance of monitoring human activities that can enhance nutrient inputs, such as nitrogen and phosphorus, in basins of the Brazilian semiarid region. The quantification of the emission factors analyzed here can be a tool in the development of strategies to mitigate the problems that high concentrations of N and P can bring to the quality and use of water in semiarid reservoirs.