1) What can you say about the results (cropping pattern, income, average TIF) ?
Every regulation threshold forces the farmer to have a different cropping pattern. The more regulations force the farmer to have a low average TIF, the more the farmer opts for an integrated pest management system and then an integrated production at cropping system level system. His income decreases as the regulation becomes stricter. The model chooses a cropping pattern that ensures that the average TIF is exactly equal to the maximum regulation threshold, which leads to results concerning various management systems and with several digits after the decimal point.
| Crop | Disruption level | Scenario 1 | Scenario 2 | Scenario 3 | Scenario 4 |
| TIF limit | 5 | 4 | 3 | 2.5 | |
| Total TIF | 4.5 | 4 | 3 | 2.5 | |
| Soft wheat | Rais | 33.333 | 22.917 | 2.083 | |
| Soft wheat | protI | 10.417 | 31.250 | 18.380 | |
| Soft wheat | systCl | 11.215 | |||
| Rapeseed | Rais | 33.333 | 22.917 | 2.083 | |
| Rapeseed | protI | 10.417 | 31.250 | 18.380 | |
| Rapeseed | systCl | 14.953 | |||
| Winter barley | Rais | 33.333 | 22.917 | 2.083 | |
| Winter barley | protI | 10.417 | 31.250 | 18.380 | |
| Winter barley | systCl | 11.215 | |||
| Hemp | systCI | 7.477 | |||
| Hemp | |||||
| Income | 49850 | 49115 | 47645 | 44379 |
2) Compare the results with those obtained when the State imposes regulations forcing farms to remain under a given threshold. How is it possible to carry out a cost-benefit analysis of the policy ?
This subsidy encourages farmers to implement the same practices as would a regulation imposing a maximum of 3 TIF/ha. But the difference between the two procedures lies in the income of the farmers and the cost of the public policy. In the case of a subsidy, the farmer preserves his income. For example for a 25€/ha subsidy, the farmer will earn 50145€, whereas in the case of the regulation he will earn 47645€. In the absence of all policies, whether they be regulations or incentives, his income is 49850€. The budgetary costs of the public policy is : 25*100=2500€. But in order to calculate the entire policy, it is necessary to measure the cost borne by the farmer and which corresponds to his income loss (excluding subsidy) due to a change in management system : 50145-2500-49850 = -2205. In terms of profits, the monetary value of environmental benefits linked to the TIF reduction ought to be taken into account. It is not easy to measure but it could be done based on the decrease in water pollution and therefore on the unused treatments in order to remove pesticides from drinking water.
You can download the solution and check that you wrote the model correctly and obtained the same solution : modelEco_ParisBasin_regulation.gms
