Michael Kleber:
I have no data, but if they were weighting the country by population, not by land area, I would consider the usage reasonable.
I have an August 15 statement by UN secretary-general Ban Ki-moon saying: "Nearly one out of ten Pakistanis has been directly or indirectly affected -- possibly 20 million people. One-fifth of the country is ravaged by floods." Unfortunately that's already four days after the "one-fifth" meme started. But it does suggest that, by population, only 10% of the country was "affected". As to the one-fifth, "ravaged by floods" is not the same thing as "under water". There is a second meme circulating based on the fraction "one-quarter", apparently started with the estimate of flooding having "hit" one-quarter of the country. A couple of news organizations here in Canada have stated that one- quarter of Pakistan is/remains under water!