GCM-related uncertainty in forecasting irrigation and design water requirement for paddy rice fields

Abstract

The aim of this study is to identify the global circulation model (GCM)-related uncertainties regarding the climate-change impacts that affect the water management in paddy rice fields. The crop evapotranspiration, effective rainfall, net irrigation water requirement (NIWR), and design water requirement (DWR) were simulated from 1981 to 2100 using 36 climate-change outputs of 23 GCMs. In particular, the DWR indicates the NIWR of a drought with a 10-year return period, which is used for the design of an agricultural reservoir in the Republic of Korea. The NIWR is the main factor for determining irrigation water supply and managing agricultural water resource. The average changes of the NIWR compared with the periods from 1981 to 2014 are from 5.2 to 8.3% in the central region and from 3.2 to 6.1% in the southern region under RCP (representative concentration pathways) 4.5. The largest increase from the average NIWR was simulated by the MIROC-ESM (745.8mmyear(-1)). These results showed that the selection of GCM could lead to overestimates or underestimates of the potential impacts of climate change. Therefore, water managers should consider that each GCM simulated a different NIWR to enable the application of the appropriate GCMs for drought management, water-resource development, or irrigation supply. Under the GCMS variations, an NIWR was identified, thereby allowing for a DWR estimation for which multi-GCMs were used. Under RCP 4.5, the DWR gradually increased in future periods compared with the trends from 1981 to 2014, and the average rates increased 9.4% and 6.0% in the central and southern regions, respectively. The results showed that if the capacity of an agricultural water-resource facility is maintained at its present status, an increase of the DWR may lead to water-supply shortage.