## 2 Materials and Methods
### Distributed Hydrological-Hydraulic Modelling
#### 2.2.4 Infiltration  
We adopted the Soil Conservation Service (SCS) Curve Number (CN) approach for evaluating the infiltration parameter \(I\) (1) in the distributed hydrological simulation of the Manillas agricultural watershed. In particular, we used a continuous version of the curve number methodology [72]. The theoretical foundations of the SCS-CN are well described in the book by [PERSON] et al. [73]. Details on the numerical implementation in the distributed-hydrological model IBER+ can be found in the software manual [74]. For brevity, we describe the parametrisation of the model for our simulations concisely.  
The model relies on a single parameter--called a Curve Number (CN)--that depends on the hydrologic soil group and the soil use and management. In the urban area, irrigation ponds and roads of Figure 4, we set the impermeable condition \(I=0\) corresponding with \(CN=100\). Based on the surface texture of the olive grove region, gullies, and streams, the hydrologic soil group is sandy clay loam (group C [73]). Such soils have low infiltration rates when thoroughly wetted. Indeed, [PERSON] et al. [18] reported soil water repellence, i.e., \(I=0\), under conventional tillage in olive-orchard catchments. Here we borrow values for the CN parameter in olive orchards from [PERSON] et al. [75], who calibrated it under different soil management in the Upper Guadalquivir watershed. Currently, the soil use and management correspond with no-tillage (Figure 4c), i.e., the soil is weed-free using herbicide. Hence, we set \(CN=89\) (see CNII in Table 6 in [75]). Such a scenario is denoted by CN89 from now on.  
The risk of high runoff depths (associated with values of CN close to 100) could be mitigated using an NbS that rises the soil surface roughness for a possible future scenario (Figure 4e). The surface outside the olive tree canopy projection could be covered by a well-implanted cover crop providing 30-70% ground cover. Hence, the CN would decrease from 89 to 64 [75]. We denote the future scenario as CN64.  
In addition, we consider a third scenario (CN100) for impermeable soils, i.e., \(I=0\) or \(CN=100\), to check the assumption that simplified the numerical modelling in our previous work [1; 6].  
To evaluate the infiltration capacity of operand flows, we accounted for the local basin slope \(S_{0}\). We corrected the CN values for scenarios CN89 and CN64 with the algebraical formula per [PERSON] et al. [76]:  
\[CN\gets CN\left[1+\frac{50-0.5\,CN}{CN+75.43}\left(1-e^{-7.125(S_{0}-0.05)} \right)\right]. \tag{8}\]  
Figure 5 shows the CN map in the Manillas stream's watershed. For completeness, we also included the computed histograms. In the present day (CN89), CN varies in the narrow range of 88-92, and in the future (CN64), CN could change to a broader interval of 60-72. In both scenarios, the most probable value tends to be the highest boundary, i.e., 92 for CN89 and 72 for CN64, highlighting the effect of the steep slopes. Indeed, the comparison between the CN maps (Figure 5a,c) with the hyposmetric map (Figure 1b) indicates a good correlation between the highest values of CN and the steepest slopes.