干旱区生态环境知识资源中心

Rainfall variability and inherent dry spells are a reality with severe implications for smallholder agro-ecosystems in semi-arid Sahel. To increase both on- and off-farm biomass production and productivity is challenging with these climate-induced temporal and spatial variations of water. This paper tests the idea that increased vegetation through tree cover may impact water balance in a water-stressed landscape: South-east Niger. Local rainfall data, farming systems data and a landscape water-modelling tool (ArcSWAT) are used. Four production domains (conventional or fertilized combined with millet crop or millet crop plus trees) were assessed for long-term yield and landscape water balance impacts. The dry-spell analysis shows a frequency of dry spells less than 14 days is in the order of one to two dry-spell events per season in 7 years out of 10 years. The occurrence has increased between 1960 and 2004, despite a slight recovery of total annual rainfall amounts since the severe droughts of the 1980s. Results of modelled millet yields and landscape water balances suggest that options exist to enhance landscape productivity. With marginal inputs of fertilizer, millet yields increased fivefold to 2.0-2.4tha-1, and water productivity improved from 6,000 to 12,000m3 actual evapotranspiration (ETa) t-1 grain, to an improved 1,700-3,000m3 ETa t-1 grain. In addition, 10% tree cover in combination with fertilized millet increased yield with marginal or no impact on water partitioning and flows in the landscape. The policy opportunities are complex and urgently needed in view of increased rainfall variability due to expected climate change. To develop sustainable pathways in these landscapes dominated by poor smallholder framers requires water managers to be more innovative and go beyond water resources alone.