Estimation of Crops’ Water Consumption by Remote Sensing: SEBAL Model Calculations Versus Ground Observation in the Irrigated Area of Lakhmass (Siliana, Northern Tunisia)

Agriculture remains a crucial sector in the Tunisian economy and is facing considerable hydric constraints due to climate change that needs to be addressed by appropriate irrigation water management. Assessing irrigation water requirements for the public irrigated areas (PIA) is therefore one of the priorities in supporting irrigation water management. In the present study, water consumption and requirements for the PIA of Lakhmass in Tunisia are assessed using remote sensing technology. PIA scale ET is estimated through the implementation of the Surface Energy Balance Algorithm for Land (SEBAL), within the Google Earth Engine (GEE) platform, by combining ERA5-land meteorological reanalysis data with visible, near-infrared, and thermal imagery satellites from high-resolution (10 m) Sentinel 2 images. The remote sensing data were combined with the seasonal supplied water to the PIA Lakhmass, collected at plot level. This study was conducted over five agricultural campaigns from 2016-2017 to 2020-2021. The results indicate that ET decreases in winter to be lower than 20 mm/month and increases in spring, 20 and 50 mm/month. During summer, it exceeds more than 70 mm/month. Furthermore, the results of the method were satisfactory, relevant, and encouraging, which could allow the monitoring of overconsumption with the identification of areas where there have been water losses. The seasonal ET was compared with water allocations which will allow calibrating the estimation of derived estimated from the SEBAL model. KEYWORDS: Evapotranspiration, Irrigation, Water use, Remote sensing, GEE, SEBAL

Assessment of the impact of contour ridge benches on the soil water content in the watershed of wadi Siliana (Medjerda basin, Northern Tunisia)

Soil water content (SWC) is one of the main parameters determining crop yields in semiarid regions. SWC is characterized by high variability, both in space and time and will be strongly impacted by climate change. Soil and water conservation techniques (SWCT), such as contour ridge bench (CRB), are often used to reduce erosion and to increase available water for crops in arid and semiarid areas. In this study, the Siliana watershed in Northern Tunisia was selected as an in-vestigation area for assessing the impact of CRB on soil water content. The im-pact of CRB on SWC was evaluated at the end of the agricultural season 2017 and 2018. To assess SWC, use was made of satellite data, obtained from the Google Earth Engine platform (GEE) and observed precipitation from gauges. The thermal optical trapezoidal model (TOTRAM) was applied to draw the rela-tionship between land surface temperature (LST) and normalized difference vege-tation index (NDVI) to estimate the SWC. 22 sites were selected one half with CRB and one other without CRB. Results indicate that the estimated SWC in ar-eas with CRB is significantly higher than those without CRB, suggesting the beneficial effect of CRB on SWC. The additional SWC varies among sites be-tween 1 and 6 %, during March to early May, and drop to be in range less than 1 % during late May and June, at the end of the cropping season

Participatory monitoring of river flows.

Water users in northwestern Tunisia, like the Medjerda watershed, are increasingly withdrawing water from hydro-systems. This is a response to the effects of climate change that are causing strong variability. These water withdrawals result in an increase in the state of stress over time (Fehri et al., 2020). The involvement of citizens, in a participatory manner, is likely to help raise awareness among water users. The use of Mobile application has been validated in the region of Medjez El Bab by the involvement of different citizen groups (Fehri et al., 2020a; Fehri, 2021). The objective of this sheet is to capitalize on these achievements and to be used in the north-west of Tunisia for monitoring droughts or floods