How Can We Represent Seasonal Land Use Dynamics in SWAT and SWAT+ Models for African Cultivated Catchments?

Abstract

In SWAT and SWAT+ models, the variations in hydrological processes are represented by Hydrological Response Units (HRUs). In the default models, agricultural land cover is represented by a single growing cycle. However, agricultural land use, especially in African cultivated catchments, typically consists of several cropping seasons, following dry and wet seasonal patterns, and are hence incorrectly represented in SWAT and SWAT+ default models. In this paper, we propose a procedure to incorporate agricultural seasonal land-use dynamics by (1) mapping land-use trajectories instead of static land-cover maps and (2) linking these trajectories to agricultural management settings. This approach was tested in SWAT and SWAT+ models of Usa catchment in Tanzania that is intensively cultivated by implementing dominant dynamic trajectories. Our results were evaluated with remote-sensing observations for Leaf Area Index (LAI), which showed that a single growing cycle did not well represent vegetation dynamics. A better agreement was obtained after implementing seasonal land-use dynamics for cultivated HRUs. It was concluded that the representation of seasonal land-use dynamics through trajectory implementation can lead to improved temporal patterns of LAI in default models. The SWAT+ model had higher flexibility in representing agricultural practices, using decision tables, and by being able to represent mixed cropping cultivations.

Regionalization of the SWAT+ model for projecting climate change impacts on sediment yield: An application in the Nile basin

“…The SWAT+ model simulates agricultural land use by default in a generic way where the phenological development of crops from planting is driven by accumulated heat units ( Arnold et al, 1998 ). However, this approach may not work for tropical and sub-tropical regions where crop growth is mainly controlled by rainfall rather than temperature ( Alemayehu et al, 2017 , Alemayehu et al, 2017 , Nkwasa et al, 2020 ). Hence, the use of heat units in crop scheduling could lead to inconsistencies in crop phenology simulations, especially for tropical and subtropical regions.…”

Can the cropping systems of the Nile basin be adapted to climate change?

“…Crop phenology data with different cropping systems (Fig. 1b) and crop management practices of fertilization and irrigation were incorporated in the model using decision tables (Nkwasa et al 2020(Nkwasa et al , 2022a. Decision tables are a precise way to model rule sets and the corresponding actions by allowing a user to add conditions for scheduling management in the model (Arnold et al 2018).…”

Representation of hydrological processes in a rural lowland catchment in Northern Germany usingSWATandSWAT+

“…SWAT+ applications in Africa focused on improving model performance through hydrological mass balance calibration and better representation of reservoir and irrigation management in Southern Africa (Chawanda, Arnold, et al, 2020), on introducing a user‐friendly software for generating reproducible SWAT+ model setups using the Upper Blue Nile as an example (Chawanda, George, et al, 2020), on an improved representation of seasonal land use dynamics in Tanzania (Nkwasa et al, 2020), and on using high resolution gridded data to analyse the surface runoff response to land use and climate change in Kenya (Kiprotich et al, 2021). In Europe, Senent‐Aparicio et al (2021) developed a post‐processing tool for calculating environmental flows that is included in the QGIS interface of SWAT+ and tested it in the Eo River basin in Spain.…”