Potential Response of Two Crops Irrigation Water Requirements to Some Potential Climate Change Scenarios.

The impact of potential future climate change scenarios on the irrigation water requirements (IRRs) of two Hawaiian major crops (corn and coffee) was studied using the Irrigation Management System (IManSys) model. IManSys calculates runoff, drainage, canopy interception, and effective rainfall based on plant growth parameters, soil properties, irrigation system, and long-term daily weather data (rain, evapotranspiration, and temperature). IRRs are calculated based on different water management practices. IManSys calculates evapotranspiration based on temperature data using different models. Irrigation crop water requirements of two crops (coffee and corn) were simulated for a half a century for different levels of atmospheric CO2 (330, 550, 710 and 970 ppm), temperature (+1.1 and + 6.4 C) and precipitation (+-5%, +-10% and +-20%) based of the Intergovernmental Panel on Climate Change (IPCC)  AR4 projections under current, B1, A1B1 and A1F1 emission scenarios.   IRRs decreased as CO2 emission increased. However, runoff, rain canopy interception, and excess water losses below the rootzone increased as precipitation increased. Evapotranspiration responded positively to air temperature rise, and as a result IRRs increased as well.