Discharge data derived from five water level gauges and discharge measurements in the Aguima and Niaou catchment, Benin, West Africa

This paper analyzes the hydrological processes and the impact of soil properties and land use on these processes in tropical headwater catchment in the sub-humid part of Benin (West-Africa), the Aguima catchment. The presented study is integrated in the GLOWA IMPETUS project, which investigates the effects of global change on the water cycle and water availability on a regional scale in Morocco and Benin. The lack of field investigations concerning soil and surface hydrology in the Benin research area necessitates detailed field measurements including measurements of discharge, soil water dynamics, soil physical properties etc. on the local scale in order to understand the dominant runoff generation processes and its influencing factors. This is a pre-requisite to be able to forecast the effects which global change has on hydrological processes and water availability in the region. The paper gives an overview over the hydrologic measuring concept of the IMPETUS-Benin project focusing on measurements concerning the soil saturated conductivity ksat and discharge behaviour of two different sub-catchment of the Aguima catchment. The results of ksat measurements revealed that interflow is the dominant runoff process on the hillslopes of the investigated catchment. Concerning the impact of land use on the hydrological processes infiltration experiments showed that infiltration rates were reduced on cultivated land compared to natural land cover. This results in significant differences in runoff behaviour and runoff ratios while comparing natural and agricultural used catchments.

Atmospheric, oceanic and hydrological polar motion excitation mechanisms based on a combination of geometric and gravimetric space observations

The goal of our study is to determine accurate time series of geophysical Earth rotation excitations to learn more about global dynamic processes in the Earth system. For this purpose, we developed an adjustment model which allows to combine precise observations from space geodetic observation systems, such as Satellite Laser Ranging (SLR), Global Navigation Satellite Systems (GNSS), Very Long Baseline Interferometry (VLBI), Doppler Orbit determination and Radiopositioning Integrated on Satellite (DORIS), satellite altimetry and satellite gravimetry in order to separate geophysical excitation mechanisms of Earth rotation. Three polar motion time series are applied to derive the polar motion excitation functions (integral effect). Furthermore we use five time variable gravity field solutions from Gravity Recovery and Climate Experiment (GRACE) to determine not only the integral mass effect but also the oceanic and hydrological mass effects by applying suitable filter techniques and a land-ocean mask. For comparison the integral mass effect is also derived from degree 2 potential coefficients that are estimated from SLR observations. The oceanic mass effect is also determined from sea level anomalies observed by satellite altimetry by reducing the steric sea level anomalies derived from temperature and salinity fields of the oceans. Due to the combination of all geodetic estimated excitations the weaknesses of the individual processing strategies can be reduced and the technique-specific strengths can be accounted for. The formal errors of the adjusted geodetic solutions are smaller than the RMS differences of the geophysical model solutions. The improved excitation time series can be used to improve the geophysical modeling.