I. Mamadou

What controls the isotopic composition of the African monsoon precipitation? Insights from event-based precipitation collected during the 2006 AMMA field campaign

[1] The stable isotopic composition of the tropical precipitation constitutes a useful tool for paleoclimate reconstructions and to better constrain the water cycle. To better understand what controls the isotopic composition of tropical precipitation, we analyze the d 18 O and deuterium-excess of the precipitation of individual events collected in the Niamey area (Niger) during the monsoon season, as part of the 2006 AMMA field campaign. During the monsoon onset, the abrupt increase of convective activity over the Sahel is associated with an abrupt change in the isotopic composition. Before the onset, when convective activity is scarce, the rain composition records the intensity and the organization of individual convective systems. After the onset, on the contrary, it records a regional-scale intra-seasonal variability over the Sahel, by integrating convective activity both spatially and temporally over the previous days.

Runoff evolution due to land-use change in a small Sahelian catchment

Abstract Land-use changes have been significant these last decades in West Africa, particularly in the Sahel region; in this area, climatic and demographic factors have led to a rise in cropped areas in recent decades causing strong changes in the water cycle and in river regimes. This study compares the rainfall–runoff relationships for two periods (1991–1994 and 2004–2011) in two small and similar neighbouring Sahelian catchments (approx 0.1 km2 each). This allows identification of the different hydrological consequences of land-use/land-cover change, particularly the fallow shortening and the consequent degradation of topsoil. The main land surface change is a 75% increase in crusted soil area. Runoff increased by more than 20% on average between the two periods while flood duration decreased by 50% on average. However, runoff values remained largely constant in the lower part of the northern basin due to a strong increase in in-channel infiltration. Editor D. Koutsoyiannis; Associate editor T. Wagener