“Nice weather for ducks!”, “It’s raining cats and dogs!”, “The heavens have opened….!”
We talk about rainfall a lot in this country, and sometimes it seems as if the rain never stops….but how much rain does actually fall on you? Let’s take a look at some of the Met Office figures.
Rainfall Variation
You might be surprised to know that annual rainfall in the UK can vary from less than 600mm, to over 3000mm. That’s a big difference, and it has a big effect on rainwater harvesting. Generally speaking, the East side of the country is much drier than the West. Those warm, wet westerlies bring in a lot of rain from the sea, and it tends to fall when it hits land. The presence of mountains encourages more rainfall – the rocky ridge of Crib Goch in Snowdonia National Park claimed the wettest place in the UK, with a mammoth 4635mm of rain recorded in a single year. The Highland estate of Dalness, in scenic Glen Etive, is drenched by an average of 3300mm each year. Dry days here are far outnumbered by rainy ones. In contrast, parts of Essex get just 525mm a year.
Effect On Tank Size
What does this mean for harvesting rainwater? Well, the drier the area the less rain that can be collected, therefore the smaller the storage tank. For example, you’d need twice as much roof area on Canvey Island to fill a 4000l tank, as you would in Blackburn. It’s important to size the storage tank correctly, using the average rainfall figures. The tank needs to overflow periodically as part of the water cleansing process. Too little rainfall, and too large a tank, and that won’t happen. This can result in a deterioration of the water quality.
If you have a lot of rain, then you can have a bigger tank, but size isn’t everything – your demand might not require such big tank – it’s a good idea to check the figures, and if you’re not sure how to do this, contact a specialist rainwater harvesting company, who will be happy to advise.
Drought
We don’t generally think of drought as being a problem in this country, but in fact a year of drier than usual weather during 2017, only slightly alleviated by recent storms, has left much of south-east England facing drought this summer. One water company, Southern Water, has applied for a drought permit to allow them to take more water than normally allowed from the River Medway in Kent, in an attempt to avoid water restrictions for households this summer.
Of course, rainfall is not evenly distributed throughout the year, so the summer months can often result in long, dry spells, during which gardeners may face hosepipe bans. If they have a rainwater harvesting tank that does not rely on mains water, they can continue to water the garden, veg. patch etc, using water that has previously been collected and stored during the wetter months. There is also the added bonus that rainwater is far better for most plants than tap water, and it’s great for topping up ponds too.
Conclusion
Our changing weather patterns means that it is difficult to predict the amount of rainfall variation in the future. However, regardless of how much rain falls on us, it still makes sense to collect and use as much as you can.
More information about choosing the right system can be found in our free Guide to Rainwater Harvesting Systems. Please click here to receive your copy today.
