Abubakar Salisu was terrified when he discovered arid sand in the middle of his farmland, rendering a broad strip unfit for crops. Now, extreme heat is killing his wheat before it is ready for cultivation. Wheat normally requires heat, but in the last three years, farmers in Nigeria’s far north, part of Africa's Sahel region that largely produces the country's homegrown food, have seen an “alarming” increase in heat — much more than required, said Salisu, a local leader of wheat farmers in Kaita, Katsina State.