Intensity of Storms Causing Water to be Less Available for Storage.

Two huge rains today, so far. Cats and Dogs, Lamas, Wildebeest. So much at one time we lost way too much to overflow. We increased the size of our downspouts by 33% and still cannot handle the roof run-off. Gutters are fine, Downspouts are adequate. Now the drain tile pipe in the ground is backing up. Overflows at the top. we need to increase the drain tile slope for sure so it drains away faster and possibly a larger diameter pipe. I have been watching this progress for more than ten years. Everything needs to be oversized for the extremes, since the extremes are now the norm. The drain tile backs up three feet above the ground. More slope will create more siphon effect.