Why is it so windy?

This month we have bought the polytunnel – 4mts x 2mts x 2mts – just to see how it goes – happy enough with the product but feel that there should have been somewhere to allow ropes to secure the outside. since we put this up we have had nothing but really strong winds – in one way its good as this will be a good test of the stability. My intention is to buy another one in may/june – they really are superb for setting the seeds/plants away .
Area inside the polytunnel all dug.
Raspberry bushes planted
Strawberry plants all sorted
outside of the polytunnel we have built the first raised bed – planted 1 row of Maris Piper and 1 row of King Edwards so far.
30/04/13 – just planted another row of potatoes – not sure what type , earlies lates – who knows ? it will be a surprise as these are left over shop bought potatoes that we have chitted