Modelling water-harvesting systems in the arid south of Tunisia using SWAT

Abstract

Abstract. In many arid countries, runoff water-harvesting systems support the livelihood of the rural population. Little is known, however, about the effect of these systems on the water balance components of arid watersheds. The objective of this study was to adapt and evaluate the GIS-based watershed model SWAT (Soil Water Assessment Tool) for simulating the main hydrologic processes in arid environments. The model was applied to the 270-km 2 watershed of wadi Koutine in southeast Tunisia, which receives about 200 mm annual rain. The main adjustment for adapting the model to this dry Mediterranean environment was the inclusion of waterharvesting systems, which capture and use surface runoff for crop production in upstream subbasins, and a modification of the crop growth processes. The adjusted version of the model was named SWAT-WH. Model evaluation was performed based on 38 runoff events recorded at the Koutine station between 1973 and 1985. The model predicted that the average annual watershed rainfall of the 12-year evaluation period (209 mm) was split into ET (72%), groundwater recharge (22%) and outflow (6%). The evaluation coefficients for calibration and validation were, respectively, R 2 (coefficient of determination) 0.77 and 0.44; E (NashSutcliffe coefficient) 0.73 and 0.43; and MAE (Mean Absolute Error) 2.6 mm and 3.0 mm, indicating that the model could reproduce the observed events reasonably well. However, the runoff record was dominated by two extreme events, which had a strong effect on the evaluation criteria. Discrepancies remained mainly due to uncertainties in the obCorrespondence to: M. Ouessar (med.ouessar@ira.agrinet.tn ) served daily rainfall and runoff data. Recommendations for future research include the installation of additional rainfall and runoff gauges with continuous data logging and the collection of more field data to represent the soils and land use. In addition, crop growth and yield monitoring is needed for a proper evaluation of crop production, to allow an economic assessment of the different water uses in the watershed.

Combining GIS with multicriteria decision making for siting water harvesting ponds in Northern Jordan

“…Water harvesting can significantly increase plant production in drought prone areas by concentrating the rainfall/ runoff in parts of the total area (Prinz, 1996). In many arid countries, runoff water harvesting systems support the livelihood of the rural population (Ouessar et al, 2008). The sustainability of water harvesting systems was in the past based on the 'fitting together' of the basic needs of the farmers, the local natural conditions and the prevailing economic and political conditions of the region .…”

Parameterization of the Effect of Bench Terraces on Runoff and Sediment Yield by Swat Modeling in a Small Semi‐arid Watershed in Northern Tunisia

“…In the upland's contour structures, such as bench terraces, are used as effective measure to interrupt the hill slopes (Cherif & Khaldi, ; Nasri et al, ), whereas in the hydrographic network, the construction of hill lakes is a frequently applied intervention strategy in Tunisia (Talineau et al, ). Well‐designed SWC interventions, particularly in the upland, potentially prevent or mitigate soil erosion, and their impacts on water and soil has been the subject of many studies recently conducted in Tunisia (Nasri et al, ; Lacombe et al, ; Ouessar et al, ). The positive effect of the different measures is evident – after 25 years of adoption; Tunisian SWC structures have reduced the land area threatened by erosion from 24.0% to 15.2% and reduced the siltation in dams from 28·10 6 m 3 y −1 to 17·10 6 m 3 y −1 as announced by the Ministry of Agriculture in 2014.…”

“…In the semi‐arid Tunisian context, different authors applied the Soil and Water Assessment Tool (SWAT) model (Arnold et al, ; Arnold et al, ) in order to respond to several management interventions including the impact assessment of climate change on water resource management (Sellami et al, ), while other researchers focused on the quantification of runoff and sediment transport (Bouraoui et al, ; Mosbahi et al ., 2012) or water quality interrelations with agriculture as reported by Aouissi et al (). Few Tunisian studies (Ouessar et al, ; Ouessar et al, ; Abouabdillah et al, ) targeted the impact of SWC structures on watershed hydrology and soil erosion. However, landscape pattern are variable, and the overlay of several treatment and management effects in large watersheds complicate explicit conclusions on variable SWC impacts.…”

Performance of LAI‐MODIS and the influence on drought simulation in a Mediterranean forest

“…ET 0 is computed using the Priestley‐Taylor equation (Equation , Priestley and Taylor, 1972), a simplified version of Penman‐Monteith equation (Penman, ; Monteith, ), suitable and previously used for large‐scale simulations on water‐limited biomes (Gerten et al ., , Guerschman et al ., ), and because it is easier to parameterize when spatially explicit data are missing (Fisher et al ., ). Previous study cases in the same region where data are missing, had to rely on either temporal aggregation (Lhomme et al ., ), simplified Penman‐Monteith equations (Jabloun and Sahli, ) or alternative simpler equations as Hargreaves or Priestley‐Taylor (Bouraoui et al ., , Ouessar et al ., ) leading to errors not exceeding ± 0.2 mm day −1 . Fisher et al .…”