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Assessing environmental pressures of agriculture in response to global change scenarios

Author(s): an economic modelling approach
Congress: 2008
Author(s): Loubier S., Graveline, N., Rinaudo J-D. and Gleyses G.
Cemagref UMR G-EAU

Keyword(s): Economic modelling, water demand, water pollution, global change, common agricultural policy, irrigation, agricultural economics
AbstractDuring the second half of the 20th century agricultural pressures on water resources have increased. Two of the most important pressures are irrigation water use and nitrate diffuse pollution. In response to increasing environmental concerns of the civil society, many impact assessment of public policies are conducted, among which the impact of common agricultural policy (CAP) reforms. However, studies replacing these policy reforms within a more general global change context, and assessing long term impacts, remain very rare. This article presents a methodology and results from two case studies where we assess the impact of global change scenarios on water resources. The first section presents the economic modelling methodology (based on linear mathematical programming) and its implementation in the two case studies, which main features are described. In the first one, located in Southern France, agriculture mainly generate quantitative pressures on surface water bodies, due to significant abstraction for irrigation. The area under study extends over 500 000 hectares among which 80 000 are irrigated by 3 400 farms. The cropping system is cereal oriented since 70% of the irrigated area concerns corn. .The second case study is located in the Upper Rhine valley and extends over 4200 square kilometers between Germany and France. Farming systems, whish are corn oriented, are an important source of diffuse nitrate pollution. In the second section, we describe the simulated impact of the CAP reform on water abstraction (Neste case study) and on nitrate groundwater pollution (Upper Rhine). The CAP reform scenario basically consists in a decoupling of subsidies from actual production, with differences reported between France and Germany. Simulations results show that, in the Neste, water abstraction remain stable whereas the irrigated area decreases by 5 to 30% depending on the farm types, which reflects an intensification of corn irrigation by hectare. The area which is no longer irrigated is used for growing wheat and sunflowers. In the Upper Rhine valley, we show that farms may react differently to the reform, depending on their size and production, and also on the country where they are located. German farms are less sensitive to CAP reform than French farms, the latter replacing up to 20% of their area under corn by wheat. In the third and fourth section, we construct a baseline long term global change scenarios and two contrasted variants of this scenario. The scenarios are constructed by combing assumptions related to future evolutions of main driving forces, identified through stakeholders and expert consultation. The driving forces include energy prices, cereal prices and potential development of markets for supplying the biofuel industry . Other site specific factors, like the risk of corn root worm proliferation (Upper Rhine), the possible increase of crop water requirement, or a reduction of water resources availability in response to climate change (Neste) are considered in these scenarios. We then simulate the consequences of these anticipated changes on water abstraction (Neste) and nitrate emission (Upper Rhine). The results show that different global change assumptions may lead to significant differences in results. Key determining factors are in particular expected changes in energy and cereal prices. The paper concludes with a discussion of the results and highlight, how such economic models can be coupled with bio-physical ones (soil-crop and hydrogeological modelling) to develop long term decision support systems. Potential methodological improvements like dynamic typologies, able to take into account farm size evolution and types death, are also discussed.
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