Sustainable water management in semi-arid agriculture practices requires quantitative knowledge of water fluxes within the soil-vegetation-atmosphere system. Therefore, we used stable-isotope approaches to evaluate evaporation (Ea), transpiration (Ta), and groundwater recharge (R) at sites in Senegal's Groundnut basin and Ferlo Valley pasture region during the pre-monsoon, monsoon, and post-monsoon seasons of 2021. The approaches were based upon (i) the isothermal evaporation model (for quantifying Ea); (ii) water and isotope mass balances (to partition Ea and Ta for groundnut and pasture); and (iii) the piston displacement method (for estimating R). Ea losses derived from the isothermal evaporation model corresponded primarily to Stage II evaporation, and ranged from 0.02–0.09 mm d-1 in the Groundnut basin, versus 0.02–0.11 mm d-1 in Ferlo. At the groundnut site, Ea rates ranged from 0.01 to 0.69 mm d-1; Ta was in the range 0.55–2.29 mm d-1; and the Ta/ETa ratio was 74–90%. At the pasture site, the ranges were 0.02–0.39 mm d-1 for Ea; 0.9–1.69 mm d-1 for Ta; and 62–90 % for Ta/ETa.  The ETa value derived for the groundnut site via the isotope approach was similar to those from eddy covariance measurements, and also to the results from a previous validated HYDRUS-1D model. However, the HYDRUS-1D model gave a lower Ta/ETa ratio (23.2%). The computed groundwater recharge for the groundnut site amounted to less than 2% of the local annual precipitation. Recommendations are made regarding protocols for preventing changes to isotopic compositions of water in samples that are collected in remote arid regions, but must be analysed days later. The article ends with suggestions for studies to follow up on evidence that local aquifers are being recharged via preferential pathways

Pastoral farming in sylvo-pastoral systems remains a key activity for the local economy and food security in the Sahel. Livestock has a great impact on the carbon cycle and on greenhouse gas (GHG) fluxes. Over the last decade, experimental and modeling studies have addressed the variability of ecosystem GHG fluxes, their drivers and efforts at scaling. Nonetheless, in these Sahelian semi-arid ecosystems, there is still limited information on the underlying processes as well as temporal and spatial variability of GHG fluxes, preventing their quantification from local-to-regional scales. This lack of information is mostly due to the paucity of experimental data, but also modeling studies required at the regional scale. We used STEP (Sahelian Transpiration Evaporation and Productivity model), an ecosystem process model for Sahelian herbaceous savannas to investigate the underlying processes of carbon dioxide (CO2) and nitrous oxide (N2O) emissions in a typical sylvo-pastoral system of the Sahel (Dahra, Senegal). Overall, good agreements have been found between model outputs and validation in-situ data for soil moisture, evapotranspiration, soil mineral and organic N, soil C, and herbaceous mass. Dynamics of the model output of N2O and CO2 fluxes clearly show emission pulses after the first rains as generally observed in dry ecosystems. Following calibration and validation at the local scale, the model will be used to assess GHG emissions from different sites across the Sahel. GHG flux maps, validated by in situ measurements, will then be proposed at the scale of the Sahelian region for sylvo-pastoral ecosystems.