Question

Which question has been addressed in this step?

Exploring risks: How will climate change affect water availability, crop yields and crop water requirements?

Why has this question been chosen?

• Overall impacts of climate change on water resources are expected to be negative. Climate change will make less water available to produce food crops in the years to come. Rising temperatures will translate into increased crop water requirement which would ultimately affect crop production.

Which methods have been applied?

• Projections of temperature, precipitation, solar radiation, relative humidity, wind speed, sunshine, and reference evapotranspiration input into a hydrological model (WEAP) and a crop model (Aquacrop). On-farm adaptation options can be simulated by changing the type of irrigation system, water applied, irrigation schedule and changes in the crop cycle. Outfarm adaptation options can also be simulated by introducing new sources of water supply (e.g. new dams) or new methods to improve the technical water use efficiency (e.g. rehabilitation of irrigation distribution systems). The methodology includes a last stage consisting on the validation of results and evaluation of the models by stakeholders.

Why have these methods been selected?

• Past experience of other research projects on the same basin. Model results are generally easily understood and well accepted by stakeholders.
• Models are user friendly, easy to handle by scientists from different disciplines and experts (e.g. policy makers).
• Regional climate projections available from Spanish Climate Change Office and from other MEDIATION partners (SYKE)

What results have been obtained?

• Crop water requirements are very sensitive to climate variations. They increase under drought conditions especially in the driest areas (midstream and downstream regions).
• In a business-as-usual scenario, water shortages might occur in dry years and summer periods,, which evidence a clash between the use of water for agriculture and the use of water for the environment.
• Water needs will increase for all crops except for maize (probably due to a reduction in the crop cycle) under the B2 and A2 climate change scenarios, but yields will increase to a bigger extent. This combination could have positive impacts on farms.

Reflections on this step

• Some assumptions in the models could have led to an overestimation of yield results.
• We would like to revise the assumptions taken in the crop model and rerun simulations.
• We would like to simulate additional climate model scenarios to further characterize impact uncertainty. Stakeholders found these models very useful for the simulation of scenarios and found that results fitted reality.