Blogging from the Murcia region of Spain until early June, when I return to
the Highlands of Scotland for a few months

'Fair and softly goes far' - Miguel de Cervantes

Tuesday, 29 September 2009

Converting different measures of rainfall

Here in Spain (and in Europe generally, I think) rainfall is measured in terms of litres per square meter over a given period. The period during which the rainfall is experienced is obviously important, because if 100 litres of rain falls in say, 12 hours, that will be a very different thing than if that same volume of rain falls evenly over a month. The former would be a downpour, the latter a light to moderate rain.

In the UK and the US (and probably much of the English-speaking world) rainfall is measured differently. We measure it in inches of rain, usually per year for standardised measurement comparisons. In Scotland (where I come from) the east coast tends to have less rain (perhaps 25 to 30 inches of rain per year) than the west coast, which can have in excess of 100 inches of rain per annum, because it is directly exposed to the prevailing moisture-laden westerly winds from the Atlantic Ocean.

But how to convert these two measuring systems to the other? Well, basically a rainfall of 10 litres per square meter is equivalent to 10mm (1cm) of rain. The conversion factor between centimetres and inches is 2.54, so 1cm of rain is .3937 inches. 100 litres is therefores 100mm (10cm) or 3.937 inches - or approx 4 inches.

Yesterday I wrote about the heavy rainfall that had been experienced in the Murcia region of Spain over the past few days and I mentioned that 80 litres of rain had fallen in the Campo de Cartagena in the previous day (Sunday) - that is therefore over 3 inches of rain in 24 hours. That's a lot of rain, by any standards!

(PS/ I did the research for this short article for my own interest, because I didn't understand before what the local rainfall readings here mean in terms that I am more familiar with, but I hope these notes may be useful for others, too.)

2 comments - please add your own:

BRIAN said...

AMAZING BILL. I HAVE JUST BEEN LOOKING UP VARIOUS SITES TO GET THIS INFORMATION. HAVING SEEN ON TV LAST NIGHT THAT WE MAY GET 100 LITRES PER METER TODAY IN OUR AREA !. NOT AT ALL FAMILIAR WITH THIS METHOD OF MEASURING RAINFALL BUT NOW HAVE MADE A CHART,
REASON IT IS SO AMAZING ?. I AM ON THE COSTA CALIDA TOO, HAVE LOOKED AT WEBSITES ALL AROUND THE WORLD AND GOT CONFLICTING INFORMATION. FINALLY GOT IT CLEAR AND PRECISE FROM NEAR HOME. (TOTANA) THANKS. Brian Williamson

BRIAN said...

THANKYOU. BRIAN W. (TOTANA)