AMMA-CATCH observatory: Gourma mesoscale site (30 000 km2) in the Sahelian pastoral zone, Mali

The northernmost site of the AMMA-CATCH observatory, the Gourma meso-scale site in Mali, is located between 14.5°N and 17.5°N in the Sahelian zone sensu stricto stretching mainly from the loop of the Niger River southward down to the border region with Burkina-Faso. It also reaches the Saharo-Sahelian transition zone, north of the Niger River. The climate is semi-arid, daytime air temperatures are always high and annual rainfall amounts (from about 100 mm in the northern part to about 450 mm in the southern part of the site) exhibit strong inter-annual and seasonal variations. The region is mainly pastoral and agriculture fields cover less than 1% of the Gourma. Measurements sites are organized along the north–south rainfall transect on two main types of soil surfaces and hydrologic systems which reveal sharp gradients in soil moisture, vegetation cover and energy budget: a) sandy soils with high water infiltration rates and limited run-off, that support an open tree savannah; b) shallow soils characterized by a poor water infiltration and a sparse vegetation, with more concentrated run-off that ends in pools or low lands within structured endorheic watersheds. Seasonally inundated lowlands are covered by open Acacia forests. Since 2010, due to security issues, field measurements are restricted within the Hombori super-site.