Improving the Applicability of the SWAT Model to Simulate Flow and Nitrate Dynamics in a Flat Data-Scarce Agricultural Region in the Mediterranean

Abstract

Understanding the soil and hydrologic processes in agricultural watersheds are vital for reliable assessments of water quantity and quality to support integrated river basin management. However, deriving hydrology-relevant information is complicated in flat data-scarce agricultural watersheds due to constraints in watershed delineation, flat topography, poor natural drainage, and irregular irrigation schedules by human intervention. The study aimed to improve the applicability of the Soil and Water Assessment Tool (SWAT) model to simulate daily flow and NO3 concentrations in a flat data-scarce agricultural watershed in the Lower Seyhan Plain (LSP) in Turkey. Refined digitized stream networks, discharge data derived from fully equipped gauging stations, and satellite data (Landsat 7 ETM+, Aster GDEM, etc.) had to be integrated into the modeling process to improve the simulation quality. The model was calibrated using a 2-year (2011–2012) dataset of streamflow and NO3 using the Sequential Uncertainty Fitting (SUFI-2) approach and validated from 2013 to 2018. Daily water yields were predicted with a reasonable simulation accuracy (E values ranging from 0.53 to 0.82 and percent bias (PBIAS) from 0 to +4.1). The results proved that integrating redefined stream networks to SWAT within a Geographic Information System (GIS) environment increases the simulation capability of flow and nitrate dynamics efficiently. Automated delineation of these networks and sub-basins at low topographic transitions limits the SWAT accuracy.

Effects of agricultural activities on water quality: catchment-scale modeling of nutrient pollution and management in cultivated lands, case studies of northern spain and southeastern sweden

“…Similar findings have also been reported by Donmez et al (2020), who inferred that an increase in fertilization would lead to an increase in the amount of nitrate in the soil, which would be directly related to plant growth and agricultural production and management. According to Abbaspour et al (2015), nitrate dynamics in agricultural watersheds are governed mainly by the fate and transportation of fertilizer in the soil, the rate of organic matter decomposition, and the prevailing climate.…”

Effects of local land-use policies and anthropogenic activities on water quality in the upstream Sesan River Basin, Vietnam

“…SWAT description. SWAT is a well-known physical-hydrological model used to predict the impact of land-use changes and land management practices on river discharge (Hanief and Laursen, 2017), sediment (Shi and Huang, 2021), and nutrients (Epelde et al, 2015;Donmez et al, 2020) over long periods on the river basin scale. The hydrological cycle in SWAT is based on the water balance equation, in which surface runoff is estimated through the SCS curve number equation as follows:…”

“…Information such as the amount of fertilizer per crop and its timing should be updated in the model along with the changes in landuse policies because the significant impacts of agricultural practices on the hydrology, crop yield, and water quality processes have been emphasized (Arabi et al, 2007;Srinivasan et al, 2010;Donmez et al, 2020). The agricultural practice information for the timing of planting, fertilizing, and harvesting was collected from the local government.…”

Impacts of Rainfall Variability on Streamflow in the Drylands of Northern Kenya: Assessing Water Availability under a Changing Climate

“…Availability of water may be assessed using trends and variability of streamflow resulting from rainfall events (25). This requires collection and analysis of basic hydrologic data that include rainfall, temperature, LULC, Digital Elevation Map (DEM), and stream flow (26,27). This paper used a hydrological modelling approach to quantify and predict biophysical water availability using SWAT hydrological model (28).…”