The AMMA-CATCH experiment in the cultivated Sahelian area of south-west Niger – Investigating water cycle response to a fluctuating climate and changing environment

Abstract

International audienceAmong the three sites distributed along the West African latitudinal gradient in the AMMA-CATCH observation system, the experimental setup in the Niamey area of south-west Niger samples the cultivated Sahel environment, for hydrological, vegetation and land surface processes. The objective is to investigate relationships between climate, land cover, and the water cycle, in a rapidly changing semiarid environment. This paper first presents the main characteristics of the area, where previous research, including the EPSAT and HAPEX-Sahel experiments, had evidenced a widespread decadal increase in water resources, concurrently with severe drought conditions. The specifics of AMMA-CATCH research and data acquisition at this site, over the long-term (not, vert, similar2001–2010) and enhanced (not, vert, similar2005–2008) observation periods, are introduced. Objectives and observation strategy are explained, and the main characteristics of instrument deployment are detailed. A very large number of parameters – covering rainfall, vegetation ecophysiology, phenology and production, surface fluxes of energy, water vapour and CO2, runoff and sediment, pond water, soil moisture, and groundwater – were monitored at local to meso scales in a nested structure of sites. The current state of knowledge is summarized, connecting processes and patterns of variation for rainfall, vegetation/land cover, and the terrestrial hydrologic cycle. The central role of land use and of its spectacular change in recent decades is highlighted. This paper provides substantial background information that sets the context for papers relating to the south-west Niger site in this AMMA-CATCH special issue

Mapping surface soil moisture over the Gourma mesoscale site (Mali) by using ENVISAT ASAR data

“…In the framework of the AMMA project, meso-scale sites have been instrumented in Mali, Niger and Benin, providing ground data along the latitudinal gradient between Sahelian and Sudanian bioclimatic regions Cappelaere et al, 2009;Mougin et al, 2009a;de Rosnay et al, 2009).…”

Building a field- and model-based climatology of local water and energy cycles in the cultivated Sahel – annual budgets and seasonality

“…This continuous series was obtained by combining a unique field data set over that period Cappelaere et al, 2009;Ramier et al, 2009) with the physically based SiSPAT (Simple Soil-Plant-Atmosphere Transfers) model (Braud et al, 1995). The study area is located in the so-called central Sahel region, which is considered the most representative of the West African monsoon rainfall regime (Lebel and Ali, 2009).…”

Time Series Analysis of Floods across the Niger River Basin

“…The most likely explanation for the more strongly increasing AMAX compared to precipitation is therefore a stronger effect of land-use change compared to other regions [23]. This effect was found by several detailed studies on effects of land-use changes for the Sahel region [3,[69][70][71]. However, the role of the groundwater in the region is also very complex and should be addressed systematically in order to see how it influences high flows [72,73].…”