> What you are showing here is probably a decline in average temperature.

While I agree relative humidity has its flaws, this isn't true. Assuming OP is in the northern hemisphere, temperature is indeed dropping. However, cold air stores less water, so the relative humidity for the same amount of water would go up, not down.

If OP is in the southern hemisphere, then I would question if what they are plotting is actually an improvement due to the remedial works or just a rise in temperature.