A historic drought in the southern Plains intensified in the last week and contributed to dry conditions emerging in the heart of the Midwest crop belt, a weekly climatologists’ report said Thursday. The weekly U.S. Drought Monitor, produced by a consortium of national climate experts, showed abnormally dry conditions affecting a significant area of the Midwest — about 10 percent — for the first time this summer. The areas included parts of Iowa and Illinois, the top two corn- and soy-growing states that annually produce about one-third of the U.S. corn crop. Also affected were southern Wisconsin, northeast Indiana, northwest Ohio and southeast Michigan. Texas remained the epicenter of the crisis, with “exceptional drought,” the most severe drought category, gripping 75 percent of the state. Texas climatologist John Nielsen-Gammon said it was the state’s third-worst drought since 1895.