# Slope Adjustments

The moisture condition II curve numbers provided in the tables are assumed to be appropriate for 5% slopes. Williams (1995) developed an equation to adjust the curve number to a different slope:

$$CN_{2s}=\frac{(CN_3-CN_2)}{3}*[1-2*exp(-13.86*slp)]+CN_2$$       2:1.1.12

where $$CN_{2s}$$ is the moisture condition II curve number adjusted for slope, $$CN_3$$ is the moisture condition III curve number for the default 5% slope, $$CN_2$$ is the moisture condition II curve number for the default 5% slope, and $$slp$$ is the average fraction slope of the subbasin. SWAT+ does not adjust curve numbers for slope. If the user wishes to adjust the curve numbers for slope effects, the adjustment must be done prior to entering the curve numbers in the management input file.

Table 2:1-1: SWAT+ input variables that pertain to surface runoff calculated with the SCS curve number method.

| Variable Name | Definition                                                                                                                                                             | Input File |
| ------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ---------- |
| IEVENT        | Rainfall, runoff, routing option.                                                                                                                                      | .bsn       |
| ICN           | Daily curve number calculation method: 0 calculate daily CN value as a function of soil moisture; 1 calculate daily CN value as a function of plant evapotranspiration | .bsn       |
| CNCOEF        | $$cncoef$$: Weighting coefficient used to calculate the retention coefficient for daily curve number calculations dependent on plant evapotranspiration                | .bsn       |
| PRECIPITATION | $$R_{day}$$: Daily precipitation          (mm H$$_2$$O)                                                                                                                | .pcp       |
| CN2           | $$CN_2$$: Moisture condition II curve number                                                                                                                           | .mgt       |
| CNOP          | $$CN_2$$: Moisture condition II curve number                                                                                                                           | .mgt       |
