Frequent poor harvests in rainfed agriculture have resulted in recurring food shortages in Niger for decades. The predicted climate change during this century is expected to worsen the situation. Dry season irrigated horticulture has been adopted as a coping strategy. However, improved management technologies are necessary for farmers and others in the agricultural system to adapt to water scarcity and the adverse effects of future climate change. The present study investigated the irrigation requirements and the optimum planting periods for cabbage, potato, tomato, onion, and sweet pepper at Niamey, Bonkoukou, Keita, Galmi, and Diffa, respectively, using the DSSAT and CROPWAT models. Predicted climate data from 16 General Circulation Models included in the ClimateWizard program have been used with those crop models to analyze the impacts of the future climate change on the irrigation requirements and the crop yield.

The average daily irrigation water requirements based on the climatic normal period 1981-2010 were estimated to be 8 mm for potato, tomato, and cabbage; and 6 mm for onion and sweet pepper. Based on the predicted temperature increases, the seasonal irrigation water needs will increase by 7% by mid-century and 11% by end-century for cabbage, potato, and tomato. Lesser increases were found for the sweet pepper and onion irrigation water needs with respectively 2% and 3% for mid-century, and 7% and 5% for end-century. The yield of all the five crops is expected to decrease progressively by the mid-century (2050) and end-century (2100) timelines. Tomato and potato yield were found to be the most impacted, including a possible total loss of the potato tuber yield by the end of the century.

The results showed that early November would be the optimum planting periods for cabbage, tomato, and potato in terms of lower crops irrigation water needs and maximum potential yield. While for sweet pepper and onion, transplanting the seedlings in the early September would be a good management strategy.

The suggested adaptation measures to climate change include the development of heat-tolerant varieties, the promotion of rainy season vegetable growth, the switching to other cropping systems in areas where heat sensitive crops will be difficult to grow, extension of onion and sweet pepper to other locations of the country.