You know, you really should read the article. You might learn something.
The researchers are reporting the same phenomena in "hot farming areas in Sri Lanka, Egypt and the Indian east coast."
However, as a couple of people have already suggested, this may be nothing more than better diagnosis and reporting: the deaths were previously attributed to unknown or an incorrect cause.
Grasp of the obvious, different elevations dictate different water source contaminants, be it chemical, mineral, or biological.
Wow, did you come up with that all by yourself? Do you think no one has thought of it? If you had read the article:
"There are other ways to damage the kidney. Heavy metals, chemicals, toxins have all been considered, but to date there have been no leading candidates to explain what's going on in Nicaragua ... As these possibilities get exhausted, recurrent dehydration is moving up on the list."
Even the reporter for this particular mainstream media outlet has done a reasonable job of anticipating your questions before you posed them, and I doubt it's an exhaustive summary of the research.
kma