Abstract
The recent increase in global consumption of rice has led to increased demand for sustainable water management in paddy cultivation. In this study, we propose an enhanced paddy simulation module to be introduced to Soil and Water Assessment Tool (SWAT) to evaluate the sustainability of paddy cultivation. The enhancements added to SWAT include: (1) modification of water balance calculation for impounded fields, (2) addition of an irrigation management option for paddy fields that are characterized by flood irrigation with target water depth, and (3) addition of a puddling operation that influences the water quality and infiltration rate of the top soil layer. In a case study, the enhanced model, entitled SWAT-Paddy, was applied to an agricultural watershed in Japan. The results showed that the SWAT-Paddy successfully represented paddy cultivation, water management, and discharge processes. Simulated daily discharge rates with SWAT-Paddy (R2 = 0.8) were superior to the SWAT result (R2 = 0.002). SWAT-Paddy allows the simulation of paddy management processes realistically, and thus can enhance model accuracy in paddy-dominant agricultural watersheds.
Highlights
Rice is the staple food of more than half of the world’s population and supplies more dietary energy than many other grain crops [1]
Using the best parameter set gained in the calibration process, the Nash Sutcliffe model efficiency (NSE), Ratio of RMSE to the standard deviation of the observations (RSR), and percent bias (PBIAS) of the daily river flow simulation (Figure 6) were measured to be 0.63, 0.61, and 1.57, respectively, which indicates that the hydrological simulation is “satisfactory” [55]
TAhTe-cPoamddpyar(iNsoSnEo=f F0i.4g0uraensd6 Ran2 d= 01.151sh) owwass tlhoawtetrhethbaansethflaotwofgtrheeatolyrigdiencarleamsoeddeoln(cNeStEhe=i0rr.6ig3aatinodnRp2e=rio0d.63h)a.dThstearctoemd,pwarhiiscohndoifdFnigout roecscu6rainndth1e1 oshbosewrvsathtiaotnt.hTehbeasceomflopwargisroeantloyf dtheecrceoarsreedlaotinocnesthoef SirWrigAaTtiaonndpSerWioAdTh-Padadsdtayrtaegda,iwnshticthhedoidbsneortvoacticounr ainlsothreevoebalsserthveatpioono.r TmhoedecloamcpcuarraiscoynofoSf WthAeT-cPoarrdedlaytifoonr sbaosfeflSoWwAsTimaunldatiSoWn (AFTig-uPraed1d2y). aTghaeinPsBt IAthSe calculated for the irrigation period (May to August) and the non-irrigation period (Table 6) showed a trend in which Soil and Water Assessment Tool (SWAT)-Paddy underestimated the river flow in the irrigation period, and overestimated it in the non-irrigation period, more than the SWAT estimates, and the magnitude of bias was almost doubled in SWAT-Paddy. These results suggest that SWAT-Paddy has the problem of poor base flow estimation in this watershed, which is characterized as a lowland paddy field watershed
Summary
Rice is the staple food of more than half of the world’s population and supplies more dietary energy than many other grain crops [1]. Several methods are generally used: increasing the number of rice cultivations per year, improving crop yield potential with genetic modification, or applying more agrochemicals, fertilizers, and irrigation [3]. Paddy fields are cultivated under inundation of irrigated water, as these consume and discharge a large volume of water. To mitigate the impact on water quality in watersheds containing paddy fields, a management plan for land use, irrigation, and drainage should be employed. The Soil and Water Assessment Tool (SWAT) is one of the hydrological models used to assess the sustainability of land and water resources, considering agricultural production at the watershed scale [10,11]. The SWAT model has significant potential to help administrators make sustainable management plans for watersheds with paddy fields
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