Coping with Rainfall Variability: Dry Spell Mitigation and Implication on Landscape Water Balances in Small-scale Farming Systems in Semi-arid Niger

Abstract

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 2.0-2.4 t ha 21 , and water productivity improved from 6,000 to 12,000 m 3 actual evapotranspiration (ET a ) t 21 grain, to an improved 1,700 -3,000 m 3 ET a t 21 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.

Growing water scarcity in agriculture: future challenge to global water security

“…Dry spells cause green water scarcity without necessarily causing reductions in seasonal or annual rainfall [20]. In field studies in the Sahel, Rockström [21] showed that dry spells disturb the root uptake capacity, which can result in large evaporation losses and therefore low yields [22].…”

Agricultural drought trends and mitigation in Tillaberí, Niger

“…Nevertheless, the presented results agree with recent findings in the literature and can therefore be assumed to correspond to a general tendency. Also, Barron et al (2010) and Balme et al (2006) both indicated a recovery of the total rainfall amount at the end of the 20th century in the region, and respectively point out an increase in dry spell occurrence and a decrease in the number of rainfall events. We were unfortunately unable to determine from these data whether the general tendency of an increasingly erratic rainfall distribution was uniquely caused by climate change, as in addition to climate change, land use change might also drive or enhance changes in rainfall distribution by deforestation or by increasing human agricultural exploitation, leading to land degredation (IPCC 2007;Mahé and Paturel 2009).…”

“…Yet these droughts were not unprecedented, as the Sahel has historically always witnessed alternating humid and arid periods (Nicholson 2001;Mishra and Singh 2010). More recent studies in fact speculate about a shift toward a less arid state and about rainfall recovery with wetter years from the 1990s onward (Greene et al 2009;Nicholson 2005;Balme et al 2006;Mahé and Paturel 2009;Barron et al 2010;Elagib 2010). …”

“…A decisive answer on what the causes and extent of both meteorological and soil-water drought are is crucial to enable effective policy and resilience, but adaptation to future climate change often entails the very same practices as rehabilitating degraded land to enhance water productivity (Barron et al 2010). Water and soil conservation (WSC) techniques, for instance, alter the root zone water balance to increase the amount of water stored in the soil profile, while building resilience to possible climate change-induced dry spells.…”

Risks and opportunities from more productive and resilient cropping system strategies in the Central and Southern Rift Valley of Ethiopia

“…It governs the crop yields and determines the choice of the crops that can be grown (Tesfaye & Walker 2004b;Lansigan 2005). Therefore, a detailed knowledge of rainfall behaviour which includes information concerning the trends or changes of precipitation (Osman & Sauerborn 2002;Admassu et al 2007a;Cheung et al 2008); the start, end and length of the growing period (Camberlin & Okoola 2003;Marteau et al 2011) and the risk of dry and wet spells, is an important prerequisite for agricultural planning (Simane & Struik 1993;Tesfaye & Walker 2004a;Barron et al 2010).…”