Water tables (the depth in the ground at which there's groundwater) around the world have fallen in the past century or so. Its because of two things - over extraction from aquifers, and a reduction in the amount of water being retained in the ground. Less water retained is because we tend to flatten hills, fill in ponds, and redirect flows. Water stabilizes temperatures - this is why coastal places near the equator arent as hot as large land masses at the same latitude. Water can absorb a lot of heat before increasing it's own temperature - this is called 'specific heat capacity.' So what I'm asserting is, lower water tables are making it easier for wider temperature fluctuations in inland or urban areas.
Its not all bad news, though. The higher CO2 is allowing more vegetation to grow in more places, which is great for maintaining water tables. Plants covering the ground allows the ground to retain its moisture for longer - key phrase to google about this is "evapo-transpiration cycle."
If we stopped doing the kind of farming where you run a combine over rows of monoculture, and got better about using ponds to retain runoff, this would fix itself. Water tables would recharge, and increased insolation wouldn't be a worry.