Water is a fundamental resource to ensure agricultural productivity. Access to hydro-logical resources to supplement rainfall during the growing season is seen as one of the key issues for food security. For this reason, the development of agricultural systems in arid and semi-arid regions has been closely linked to the scientific and technological advances in irrigation engineering.
When water is not a limiting resource, crops can achieve high levels of productivity because the absorption of nutrients is carried out normally and the stomata are fully open, allowing gas exchange (i.e. water vapor and carbon dioxide) in an adequate manner. However, when crops are experiencing water deficits, several regulatory mechanisms take place resulting in a reduction of dry matter assimilation, mainly because the resistance to gas exchange is increased due to stomata closure, and the absorption of mineral nutrients is affected. Given the strong relationship between water transpired and dry matter accumulation, irrigation seeks to provide crops with timely water supply and in the quantities needed so that physiological stress is minimized and crops can express their yield potential (Chang 1968; Norero 1999). Two important conditions support the operation of irrigation systems in such conditions: (1) the correct estimation of crop evapotranspiration and (2) access to sufficient water resources so that the agricultural water demand can be effectively met.
The problem of irrigation management is far more complex in situations where there is a deficit in water supply. In this case, resource constraints redefine the situation, and the decision-maker seeks to reach the maximum feasible productivity of the agricultural system, particularly when several crops are competing for the limited resource, which is a traditional resource allocation problem. Decision theory states that an optimum allocation of resources is achieved when the decision-maker knows the consequences associated with all possible combinations of alternatives and states of the variable. Because climate is one of the main factors that generates uncertainty regarding final yields and given the interdependence of irrigation allocation decisions throughout the growing season, access to reliable information (i.e. climate forecasts) can generate additional economic benefits, being a tool for irrigation management.
This work illustrates the potential use of climate forecasts based on El Niño phenomenon for irrigation operation under limiting water supply conditions in central Chile, a region that has shown a significant ENSO footprint in its climatic regime. Using a methodological framework that combines stochastic modeling of meteorological variables conditioned on El Niño phases, a simple soil-crop algorithm, and a mathematical programming model, the value of climatic information is assessed. Section 9.2
summarizes the impacts of El Niño phenomenon on the climate of central Chile and the effects of climate variability on agricultural systems. Section 9.3 describes the methodological framework used to evaluate the potential additional economic benefits associated with ENSO forecasts for a case study in central Chile. Finally, Sect. 9.4 presents the results of the case study and the main conclusions of the work.
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