Azizi -

For rough - but usually close enough - calculations, one kilometer is 5/8 of a mile, and one mile is 8/5 km.

Multiply miles by 8, then divide by 5 to get km.
(The number of km is always larger than the number of miles.)

Multiply km x 5 and then divide by 8 to get miles.
(The number of miles is always smaller than the number of km.)

Re the area covered, the link (where the slide show was found) has an inset map of the current flood damage areas, and it actually is nearly as large as the central flood area from Katrina. Fortunately for the Midwest, there are only isolated areas with extreme wind damage to compound the flooding.

When planning your September shopping, it should be remembered also that it's not necessary to have a "flood" to have substantial crop damage. Areas where US cereal crop failures are already a fact are quite vast, and food prices for this growing season will undoubtedly rise significantly - with corresponding losses in income for very large numbers of farms.

John