Human appropriation of net primary production of Sahel ecosystems under a changing climate to 2050 : food security and resource-use balance in the Sahel

Responding to the food security challenge in the Sahel mainly relies on the supply of goods and services from ecosystems of the region. The evolution of the Sahelian population in the wake of climate change questions whether available biomass from agriculture and natural vegetation will be covering future human needs. To explore this issue, we present a prospective study of the human carrying capacity of Sahel ecosystems balancing its biomass supply and demand to the year 2050. This was obtained by applying a net primary production (NPP) demand and supply model based on satellite derived NPP, the most reliable information on land cover, crop types and Land Utilisation Types (LUTs), as well as official production (completed by net trade flows) statistics from FAOSTAT and UN population projections. How four alternative agriculture scenarios affect the Sahel's carrying capacity, given its variability and expected vulnerability to climate change (CC), is also addressed contrasting possible futures. Results, expressed in terms of the human appropriation of NPP (HANPP), and supported by scenario narratives, show that HANPP evolves from the current 29% (food, feed and fuel components included) to 75%-88% depending on the scenario. The approach also generated HANPP maps indicating areas of special concern ("hot spots") as well as those expected to generate opportunities ("hope spots") in terms of local NPP supply and demand balance. The two scenarios with most agricultural technological improvements achieve the most favourable NPP food share results but fall short of compensating for a more than doubling demand over the same period. Today about 15% of food biomass is imported against an expected 40% by the year 2050 and up to 65% in the least favourable scenario of this prospective. These are conservative estimates as they do not account for the likely future change in individual dietary preferences and increases in consumption. Such projections point to the need to reinforce agriculture policy with complementary assertive strategies through the diversification of the economy and adapted regional trade policy.