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.
In the Sahel, the climate and the agricultural practices are the main factors used to observe regreening process. But the extension of this re-greening is not uniform in the fields, so we can assume that there are other factors contributing to the greening of some areas and not others. The infiltrability of soils is considered as an important factor for these changes in the last decades. The influence of re-greening on the infiltrability of soils in the southern strip of Niger was studied through a comparison of zones according to the type of sandy soils (Jigawa/Rerey), silty-clay (Guiéza), silty-sandy (Hako) and clay-silty-sandy (Laka). The evaluated parameters are the texture, the infiltrability and the ecological characteristics (specific index of regeneration "SIR" and the Importance Value Index "IVI"). The main conclusions were: the soils of Niger South-Central are characterized by a sandy texture for more than 80%. The soils which are very sandy ("Jigawa", "Rerey" and "Guieza") are more permeable and have more trees contrary to the soil Hako and Laka. Their encrusting has the tendency to reduce the vegetation cover on the soil. The infiltration measurements indicated that the rate of initial and stationary infiltration diminishes while going down towards the South. In fact, it has been recorded a rate of 123 mm/min of initial infiltration and 87 mm/min stationary in Dan Saga on the sandy soils against 76 mm/min and 65 mm/min in Daré respectively for the initial and stationary rate. Therefore, the infiltration seems to influence the density, the SIR and the IVI of the trees from the North towards the South. Some additional work is necessary in order to determine the contribution of Farmer Managed Natural Regeneration (FMNR) in the improvement of the quality of soils and the movement of water in the superficial zones of the soil.
The Sahelian region is known to have extremes climatic constraints since the end of the seventies. The studied zone is characterized by an extreme spatial and temporal variability of the environmental factors, complicating the understanding of the mechanisms governing the functioning of the hydrological system in the basin. The evapotranspiration was very high (1975 mm/an), whereas the local annual rainfall was around 300 mm/year. The piezometric data showed a rise of the groundwater level during the rainy season and a decrease in the dry season. The water balance obtained using the Penman-Monteith method showed the predominance of the evapotranspiration (75% to 80% of the rainfall) on the drainage (20% to 25% of the precipitations).
The Gounti Yéna valley is the main watercourse that divides the left bank of the city of Niamey into two unequal parts. The area of its watershed is estimated at about 62 km 2 . The objective of this study is on the one hand to evaluate the current state of the physico-chemical and bacteriological quality of the water of the Gounti Yéna basin and on the other hand to define the risks of water pollution and its origin in the face of the phenomenon of the rise in the water table of this basin by defining some health risks linked to these impacts. In order to properly carry out this work, we carried out a study of the evolution of the physicochemical and bacteriological parameters of the water of the Gounti Yéna basin during the period from November 2020 to October 2021, at three sampling points chosen from upstream to downstream of the basin then entomological surveys and among the health centers of the capital. The results obtained showed that the physico-chemical quality of water in the Gounti Yéna basin is influenced by climatic factors (precipitation and temperature) and anthropogenic actions. This study also highlighted the presence of faecal contamination in the water of the Gounti Yéna basin with a greater degree during the rainy season. This contamination remains worrying and constitutes a health risk causing waterborne diseases. The stagnation of the various bodies of water is also a favorable place for the development and spread of vector-borne diseases.
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