JALALABAD, Afghanistan — The people he helped called him “Uncle Murad.”

Dr. Tetsu Nakamura left his home in Japan in the 1980s to treat leprosy patients in Afghanistan and Pakistan. He later found, however, that severe drought was killing more people than his clinics could save.

So he discovered a new calling: irrigation. In the 2000s, adapting old Japanese techniques that required little technology, he helped villagers displaced by drought build a network of canals that has transformed an area of nearly a million residents .

“A doctor treats patients one by one, but this helps a whole village,” Dr. Nakamura had said. “I love seeing a village that’s been brought back to life.”

On Wednesday, Dr. Nakamura was attacked by gunmen while driving to work in Jalalabad, the capital of Nangarhar Province, in eastern Afghanistan. Five members of his organization’s staff were killed, and Dr. Nakamura was wounded fatally . He was 73.