Soil & Water Assessment Tool (SWAT) simulated hydrological impacts of land use change from temperate grassland to energy crops: A case study in western UK

Abstract

When considering the large‐scale deployment of bioenergy crops, it is important to understand the implication for ecosystem hydrological processes and the influences of crop type and location. Based on the potential for future land use change (LUC), the 10,280 km2 West Wales Water Framework Directive River Basin District (UK) was selected as a typical grassland dominated district, and the Soil & Water Assessment Tool (SWAT) hydrology model with a geographic information systems interface was used to investigate implications for different bioenergy deployment scenarios. The study area was delineated into 855 sub‐basins and 7,108 hydrological response units based on rivers, soil type, land use, and slope. Changes in hydrological components for two bioenergy crops (Miscanthus and short rotation coppice, SRC) planted on 50% (2,192 km2) or 25% (1,096 km2) of existing improved pasture are quantified. Across the study area as a whole, only surface run‐off with SRC planted at the 50% level was significantly impacted, where it was reduced by up to 23% (during April). However, results varied spatially and a comparison of annual means for each sub‐basin and scenario revealed surface run‐off was significantly decreased and baseflow significantly increased (by a maximum of 40%) with both Miscanthus and SRC. Evapotranspiration was significantly increased with SRC (at both planting levels) and water yield was significantly reduced with SRC (at the 50% level) by up to 5%. Effects on streamflow were limited, varying between −5% and +5% change (compared to baseline) in the majority of sub‐basins. The results suggest that for mesic temperate grasslands, adverse effects from the drying of soil and alterations to streamflow may not arise, and with surface run‐off reduced and baseflow increased, there could, depending on crop location, be potential benefits for flood and erosion mitigation.

Watershed Modeling with Remotely Sensed Big Data: MODIS Leaf Area Index Improves Hydrology and Water Quality Predictions

“…These parameters represent hydrology and water quality (Tables A1 and A2, respectively) while being indirectly related to vegetation dynamics. Although SWAT is relatively well equipped with many biophysical parameters and process conceptualizations that directly influence vegetation dynamics (e.g., maximum root depth, radiation use efficiency, stomatal conductance, day/nighttime thresholds of vapor pressure deficit) [7,55], other advanced watershed models are not [23,24,56]. Therefore, we excluded such parameters from our calibration [unlike previous studies, (e.g., [8,13]) to isolate the effects of MODIS LAI assimilation into the model and to maintain focus on our study's hypothesis that assimilated LAI data can serve as a proxy for vegetation dynamics when limited (or completely absent) vegetation-related parameters and processes are available in watershed models.…”

Assessing hydrologic and water quality effects of land use conversion to Brassica carinata as a winter biofuel crop in the southeastern coastal plain of Georgia, USA using the SWAT model

“…Here, we included relevant biophysical parameters during the streamflow calibration process using the aggregated (or lumped) approach (Chen et al, 2017; Cibin et al, 2016; Demissie et al, 2017; Holder et al, 2019). Recent research in watershed modeling has shown improvements in hydrology and water quality predictions with the assimilation of remotely sensed biophysical data (e.g., LAI; Ma et al, 2019; Rajib et al, 2020).…”

“…Hydrologic models are ideal tools for predicting the hydrologic responses and nutrient and sediment loads for future scenarios at watershed scales. Soil and Water Assessment Tool (SWAT; Arnold et al, 2012) is one of the most broadly applied watershed models that has been used for evaluating the effects of biofuel‐related scenarios on hydrology and water quality (Chen et al, 2017; Cibin et al, 2016; Engel et al, 2010; Holder et al, 2019). However, many bioenergy crops such as carinata are not represented in the SWAT plant database and other watershed models.…”

Upscaling miscanthus production in the United Kingdom: The benefits, challenges, and trade‐offs

“…The water‐use efficiency (WUE) of miscanthus, due to its C 4 photosynthesis and grass leaf morphology, is much higher than most arable crops grown in Europe, with WUEs ranging from 11 to 14 g dry above‐ground biomass, per liter of water transpired, compared to 1–5 g L −1 typical for barley, wheat, and maize (Clifton‐Brown & Lewandowski, 2000; Mueller et al., 2005). However, to achieve higher biomass yields, miscanthus has a high‐water demand which can affect the hydrological balance of soils (Clifton‐Brown et al., 2002; Holder, Rowe, et al., 2019). When not irrigated, summer droughts have caused yield reductions of up to 40%–45% (Richter et al., 2008; Van der Weijde et al., 2017; Awty‐Carrol et al., unpublished).…”

“…For example, characteristics of large leaf area index, high level of rainfall interception, improved soil water infiltration, and greater capacity to extract soil water (ET) make certain miscanthus genotypes, like M. x giganteus very useful crops for land prone to waterlogging and inclusion as part of flood mitigation strategies (Holder et al., 2018; Holder, Rowe, et al., 2019). The dense, stiff‐stemmed nature of mature miscanthus grass has been shown to provide a natural barrier, reducing particulates and run‐off flow rates, and providing resistance to overland flows which make it useful as a flood defense measure by creating a leaky barrier (Holder, Rowe, et al., 2019; Shepherd, Clifton‐Brown, et al., 2020). It has also been shown to survive flooding with little impact on yield under glasshouse and winter field conditions (De Vega et al., 2021; Kam et al., 2020).…”