Fieldscale Adaptation in Seven Contrasting Basins

Although the ADAPT project focused mainly on the basin scale, attention has been paid to assessing the impacts of climate change on food at the local to field scale, including developing local response strategies. For this, the SWAP (Soil-Water-Atmosphere-Plant; van Dam et al., 1997) model was applied for calculating yields and production for two representative crops in each of the seven basins. This was done for three periods: 1961-1990, 2010-2039 and 2070-2099. Moreover, for the periods 2010-2039 and 2070-2099, the impacts of climate change on yield and production were explored under:

1. The current climate (1961-1990).

2. Climate change for 2010-2039 and 2070-2099 using the A2 and B2 scenarios from the HadCM3 climate model (see Chapter 2) and business as usual strategy.

3. Under climate change scenarios for 2010-2039 and 2070-2099 and two adaptation strategies (see the previous section).

The FAO/UNESCO Digital Soil Map of the World was used to derive soil physical parameters, required for simulating soil water processes in the unsaturated-saturated zone. Although locally more detailed soil maps might exist, we chose to use this global dataset to ensure that simulation results will not be a function of the different approaches used to generate datasets. Texture data, organic matter content and bulk density were used to derive soil physical functions (retention curve and hydraulic conductivity) by applying pedo-transfer functions as developed by Wösten et al. (1998).

The agro-hydrological analysis at field scale is performed using the SWAP 2.0 model (van Dam et al., 1997). SWAP is a one-dimensional physically based model for water, heat and solute transport in the saturated and unsaturated zones, and also includes modules for simulating irrigation practices and crop growth. The water transport module in SWAP is based on the well-known Richards' equation, which is a combination of Darcy's law and the continuity equation. A finite difference solution scheme is used to solve Richards' equation. Crop yield can be computed using a simple crop growth algorithm based on Doorenbos and Kassam (1979) or by using a detailed crop growth simulation module that partitions the carbohydrates produced between the different parts of the plant, as a function of the different phenological stages of the plant (van Diepen et al., 1989). Potential evapotranspiration is partitioned into potential soil evaporation and crop transpiration using the leaf area index. Actual transpiration and evaporation are obtained as a function of the available soil water in the top layer or the root zone for, respectively, evaporation and transpiration. Finally, irrigation can be prescribed at fixed times, can be scheduled according to different criteria, or a combination of both can be used. A detailed description of the model can be found in van Dam et al. (1997).

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