Simulation of rice paddy systems in SWAT: A review of previous applications and proposed SWAT+ rice paddy module

Authors: GASSMAN, PHILIP - Iowa State University; JEONG, JAEHAK - Texas Agrilife Research; BOULANGE, JULIEN - Tokyo University Of Agriculture & Technology; NARASIMHAN, BALAJI - Indian Institute Of Technology Madras; KATO, TASUKU - Tokyo University Of Agriculture & Technology; SOMURA, HIROAKI - Okayama University; WATANABE, HIROZUMI - Tokyo University Of Agriculture & Technology; EGUCHI, SADAO - University Of Tsukuba; CUI, YUANLAI - Wuhan University; SAKAGUCHI, ATSUSHI - Yamaguchi University; TU, LE HOANG - Tokyo University Of Agriculture & Technology; JIANG, RUI - Ministry Of Agriculture - China; KIM, MIN-KYEONG - Korean Rural Development Administration; Arnold, Jeffrey; OUYANG, WEI - Beijing Normal University

Submitted to: International Agricultural Engineering Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/14/2022
Publication Date: 2/1/2022
Citation: Gassman, P.W., Jeong, J., Boulange, J., Narasimhan, B., Kato, T., Somura, H., Watanabe, H., Eguchi, S., Cui, Y., Sakaguchi, A., Tu, L., Jiang, R., Kim, M., Arnold, J.G., Ouyang, W. 2022. Simulation of rice paddy systems in SWAT: A review of previous applications and proposed SWAT+ rice paddy module. International Agricultural Engineering Journal. 15(1):1-24. https://doi.org/10.25165/j.ijabe.20221501.7147.
DOI: https://doi.org/10.25165/j.ijabe.20221501.7147

Interpretive Summary: Rice is a staple food for almost 50% of the global population, with nearly 90% of Asia’s population reliant on rice. Multiple environmental problems have been linked to modern rice production practices, including water pollution due to over-applied and improper use of fertilizers and pesticides, elimination of beneficial insects and wildlife, excessive salt build-up and overuse of groundwater. The Soil and Water Assessment Tool (SWAT) has been used extensively in Asia to simulate impacts of rice production and management on water supply and water quality. Recent model developments point to the need for the incorporation of an enhanced rice paddy module within SWAT to better capture rice paddy hydrological and pollutant dynamics, which would support improved use of the model in Asia and other rice production regions. To meet this need, this study provides: (1) an overview of major rice production systems used in Asia and other regions, (2) a review of typical applications of SWAT that incorporate rice production including inherent weaknesses in standard simulation approaches, (3) a description of key modifications performed in recent SWAT applications that have resulted in more realistic representation of rice paddy systems, (4) a summary of the improvements and results that have been obtained with APEX-Paddy, and (5) a conceptual structure for the proposed SWAT rice paddy module.

Technical Abstract: The Soil and Water Assessment Tool (SWAT) is an ecohydrological watershed-scale model which was initially developed in the early 1990s to simulate the impacts of land use, management systems and climate on hydrology and/or water quality. First adopted in the U.S., the use of the model then spread to Europe and then later to Asia and other regions. The range of applications that SWAT has been applied to have also expanded dramatically, which influenced ongoing model development which has been virtually continuous over the past two decades. A key component of many SWAT applications in Asia is accounting for rice paddy production that is common in some subregions within the continent. However, most of these studies do not provide explicit details of how rice production was simulated in SWAT. Other research has revealed that significant problems occur when trying to represent rice paddy systems in standard versions of SWAT, due to limitations in algorithms based on the runoff curve number approach or the pothole option. In response, key modifications have been made to SWAT in recent studies that have resulted in more accurate representation of rice paddy systems. These developments point to the need for the incorporation of an enhanced rice paddy module within SWAT to better capture rice paddy hydrological and pollutant dynamics, which would support improved use of the model in Asia and other rice production regions. Subtopics related to simulating rice production in SWAT are discussed as follows: (1) an overview of global rice production, (2) history of SWAT development, (3) typical approaches for simulating rice production, (4) problems associated with the typical approaches, (5) recent code modifications to address deficiencies in replicating rice paddy systems, and (6) recommendations for developing a standard rice paddy module for future SWAT codes.