West Africa experiences great climate variability, as shown by the long-lasting drought since the 1970s. The impacts of the drought on surface water resources are well documented but remain less studied regarding groundwater resources. The nexus between climate variability and groundwater level fluctuations is poorly documented in this area. The present study focuses on the large reserve of groundwater held by the Kou catchment, a tributary of Mouhoun river (formerly the Black Volta) in the southwest of Burkina Faso, in the Sudanian region. Analyses were undertaken using climatic time series (1961–2014), two rivers’ hydrometric data (1961–2014), and 21 piezometers’ time series (1995–2014) applying statistical trend (Mann–Kendall) and break (Pettitt) tests, correlation analysis, and principal component analysis. The analyses showed that rainfall in the area underwent a significant break in 1970 with an 11%–16% deficit between the period before the break and the period after the break that resulted in a deficit three times greater for both surface and base flows. This significant deficit in flow results from the combined effect of a decrease in rainfall and an increase in evapotranspiration. The response of the catchment to the slight increase in rainfall after 1990 was highly dependent on hydrological processes. At Samendéni, on the Mouhoun River, the flow increased with a slight delay as compared to rainfall, because of the slow response of the base flow. Whereas at Nasso on the Kou river, the flow steadily decreased. The analysis showed that the groundwater level responds to rainfall with a delay. Its response time to seasonal fluctuations ranges from 1 to 4 months and its response time to interannual variations exceeds the timescale of one year. This response is highly dependent on the local aquifer’s physical characteristics, which could explain the spatial heterogeneity of the groundwater response.

Here we perform a detailed comparison between climate model results and climate reconstructions in western Europe and the Mediterranean area for the mid-Piacenzian warm interval (ca 3 Myr ago) of the Late Pliocene epoch. This region is particularly well suited for such a comparison as several quantitative climate estimates from local pollen records are available. They show evidence for temperatures significantly warmer than today over the whole area, mean annual precipitation higher in northwestern Europe and equivalent to modern values in its southwestern part. To improve our comparison, we have performed high resolution simulations of the mid-Piacenzian climate using the LMDz atmospheric general circulation model (AGCM) with a stretched grid which allows a finer resolution over Europe. In a first step, we applied the PRISM2 (Pliocene Research, Interpretation, and Synoptic Mapping) boundary conditions except that we used modern terrestrial vegetation. Second, we simulated the vegetation for this period by forcing the ORCHIDEE (Organizing Carbon and Hydrology in Dynamic Ecosystems) dynamic global vegetation model (DGVM) with the climatic outputs from the AGCM. We then supplied this simulated terrestrial vegetation cover as an additional boundary condition in a second AGCM run. This gives us the opportunity to investigate the model's sensitivity to the simulated vegetation changes in a global warming context. Model results and data show a great consistency for mean annual temperatures, indicating increases by up to 4°C in the study area, and some disparities, in particular in the northern Mediterranean sector, as regards winter and summer temperatures. Similar continental mean annual precipitation and moisture patterns are predicted by the model, which broadly underestimates the wetter conditions indicated by the data in northwestern Europe. The biogeophysical effects due to the changes in vegetation simulated by ORCHIDEE are weak, both in terms of the hydrological cycle and of the temperatures, at the regional scale of the European and Mediterranean mid-latitudes. In particular, they do not contribute to improve the model-data comparison. Their main influence concerns seasonal temperatures, with a decrease of the temperatures of the warmest month, and an overall reduction of the intensity of the continental hydrological cycle.

Gravel pit lakes created by sand and gravel mining are structural landscape elements in alluvial plains. As they create openings through the aquifer, they provide direct access to groundwater and make it possible for remote sensing to offer an integrated vision of water resources at the alluvial plain scale. Indeed the Surface Water and Ocean Topography (SWOT) satellite mission will soon map near weekly the surface water elevation of reservoirs with areal extent greater than 6 ha. Using the CNES large scale simulator, we evaluated the SWOT water level errors on gravel pits in La Bassée alluvial plain, in the middle reach of the Seine River (France). Despite their rather small size, the elevation accuracy over the artificial lakes should be centimetric. Using as input in-situ lake level measurements, SWOT-like outputs were generated. The full exploitation of these data requires a modelling tool for gravel pit lake simulation, which includes groundwater interaction. We also present the development of our lake module, imbedded in the CaWaQS platform, its validation using benchmark test problems and numerical experiments illustrating its performance in simulating gravel pit lake stage fluctuations.