## 4 Discussion  
The observed flow data used for this study are available for the period 1981-1994. It is assumed that there is no major land use and rainfall trend over this period. In ungauged hydrological catchments where there is a scarcity of historical data, this hypothesis makes it possible to simulate flow and nutrient dynamics [66]. The study revealed that flow parameters such as GW_REVAP, GWQMN, RCHRG_DP, ESCO, and CN2 impact the water flow the most. The same conclusion was made by [PERSON] et al. [67] in the Taabo watershed bordering that of Lobo. Along the same lines, [PERSON] et al. [68] showed using a study on the evaluation of flow, nutrient, and sediment transfer parameters sensitivity and uncertainty that hydrological parameters such as GWQMN, ESCO, and CN2 are sensitive to flow. ESCO and CN2 are also parameters considered to significantly influence streamflow in western Mississippi [69]. Moreover, CN2, being a parameter very sensitive to runoff, a decrease in precipitation impacts surface runoff, which will modify the values of CN2 [70; 71; 72] in [73]. However, a parameter can be identified as not sensitive. However, this does not really mean that it does not influence the flow in the watershed [74]. The values of R\({}^{2}\), NSE, and PBIAS of 0.63, 0.62, and \(-8.1\), respectively, highlighted the capacity of the SWAT model according to the evaluation criteria proposed by [PERSON] et al. [50]. Upon the Taabo watershed, similar results were obtained by [PERSON] et al. [75]. Indeed, the average NSE obtained by these authors was 0.7 during the calibration period. A PBIAS value of \(-8.1\) obtained in this study showed a very good performance of the model [50]. For flow, any P-factor > 0.7 and R-factor < 1.5 are considered acceptable. Therefore, the uncertainties on the flow predictions are considered acceptable [76]. P-factor has a value of 0.48 which is therefore less good since the wish is for this value to be close to 1 [44]. On the other hand, R-factor of 0.52 is acceptable. A model is said to be perfect when R-factor is close to 0. Very often, these values are very difficult to reach. This is why some authors recommend a balance between these two parameters [44]. In our case, P-factor is 0.48 and R-factor 0.52. There is a certain balance between these parameters. The prediction uncertainties are therefore acceptable. Despite these shortcomings of the model, the results obtained in this study constitute a solid basis for hydrological modeling in the region with a view to the fight against the eutrophication of surface water facing the population of this region. Compared with the results of the [77], the predictions of SWAT show an underestimation of the N rates of \(-9.9\%\) and of \(-5.55\%\) for P rates. The results show low inorganic nitrogen levels. These low inorganic nitrogen levels in the Lobo watershed have also been highlighted by the work of [17; 18]. This could be explained by the fact that the recommendations of agricultural advisers to farmers regarding chemical fertilizers are respected. Then, nature, including crops, is able to digest the applied fertilizers, and only a small amount remains in the environment. The flows of mineral nitrogen are lower than those of phosphorus. This difference stems from the NPK fertilizer type used. Indeed, surveys carried out with ANADER (National Agency for Rural Development Support) and CIDT (Ivorian Textile Development Company) revealed that all agricultural activities practiced in the watershed use NPK fertilizer. In fact, NPK-10-18-18 fertilizer is used equally well for Coffee, Cocoa and cotton. However, coffee and cocoa are the main industrial crops in this region of Cote d'Ivoire. This fertilizer formula contains 18% phosphorus against 10% nitrogen in 1 kg of this fertilizer, hence the high soluble phosphorus levels relative to nitrogen.