The open source R language contains packages, i.e. organized gatherings of functions, that enable to perform all steps necessary to undertake hydrological modelling (Slater et al., 2019). Especially, several hydrological models are proposed in R (Astagneau et al., 2021). In this webinar, we will give an overview of available R packages available for hydrological modelling and we will develop the possibilities of a specific package, airGR (Coron et al., 2017), which contains among other the GR4J rainfall-runoff model. References: Astagneau, P. C., Thirel, G., Delaigue, O., Guillaume, J. H. A., Parajka, J., Brauer, C. C., Viglione, A., Buytaert, W., and Beven, K. J.: Technical note: Hydrology modelling R packages – a unified analysis of models and practicalities from a user perspective, Hydrol. Earth Syst. Sci., 25, 3937–3973, https://doi.org/10.5194/hess-25-3937-2021, 2021. Coron, L., Thirel, G., Delaigue, O., Perrin, C., and Andréassian, V.: The Suite of Lumped GR Hydrological Models in an R Package, Environ. Modell. Softw., 94, 166–171, https://doi.org/10.1016/j.envsoft.2017.05.002, 2017. Slater, L. J., Thirel, G., Harrigan, S., Delaigue, O., Hurley, A., Khouakhi, A., Prosdocimi, I., Vitolo, C., and Smith, K.: Using R in hydrology: a review of recent developments and future directions, Hydrol. Earth Syst. Sci., 23, 2939–2963, https