Interesting post.


Data history:
We have a great resource on data through our state scientific surveys, and also the University of Illinois - the surveys are actually now administered through UIUC and likely worked together closely together for previous decades.  Some of this data goes back at least into the late 1800's.  The Illinois State Water Survey would be a general lead contact on rainfall data and climactic data (temp, RH, solar throughput), although NOAA and I believe also USGS, and the Illinois State Geological Survey would also maintain rainfall gages (geological surveys generally do groundwater and aquifers and stream gages and much more - there is some overlap at the edges).  NOAA and NASA have a lot newer fancier high-resolution toys with radar rainfall being ground-truthed with gages and satellite measurements of the atmosphere and the amount of water in the ground.

There are defined calibrated ISWS monitoring stations throughout the state.  I think some of these may have coincided with UIUC research farms in the past.  The most frequently noticed gages show up on their 'ground temp' website, there are a series of maybe 15-20 gages across the state.  That doesn't seem like a lot when it can rain here and not the next section over but over long periods of time, it's pretty good, and we know there are countless other data series where banks or interested individuals or coops track data.  Using the law of large numbers, you could throw them into the mix (it assumes as your data set gets bigger the errors on either side of the true accurate number balance each other out) and maybe some privates or side research uses it but I don't believe that data makes it into the official records and analysis.  

NOAA and ISWS compile rainfall data into rainfall atlases (atlii, atlai?) periodically when the existing data no longer reflects an accurate enough measure of the probabilities of a certain amount of rain falling within a given time period (a 100-year flood, or a 5-year, 24-hr rainfall event).  I tend to use ISWS data as that is what USDA used when I worked there.  This last one was maybe 8 or so years ago and the version before that was ~40 years ago.  Changing these numbers is a BIG OFFICIAL DEAL because they are foundational to lots of hydrology analyses - how big a dam needs to be, how big a stormwater detention basin will be in a subdivision, ultimately how you figure out what is the flood event and elevation where you have to get high-risk or flood insurance, etc.


Climate trends:
The IL State Climatologist puts out good summary data and presentations on trends.  Trends going back to 1880 show slow but steadily increasing precipitation.  Although the 1930's were hotter in IL than anything since, last I saw (2017?).  Kind of a dip and trending back upward.  The overall corn belt is shifting north and west (that one most recently was Snodgrass but the current IL Climatologist says it also as I recall).  If I farmed in Alberta or the Dakotas, I'd run my gas guzzler SUV hard.  Gonna be great up there I think in coming decades.  Lots of infrastructure will probably need installed and they will need good clear drainage laws and policy if they don't already have it.  Me, I'm at the southern edge of Central IL and in 30 years the weather is predicted to be like the Delta now - drenching rains, hot, humid, all creating an excellent environment for problem bugs and weeds.  

What doesn't show up in overall precipitation trends is that the weather is getting ... moodier.  Choppier.  You get your 40" of rain but you get 25% of it in a week.  Then it doesn't rain for two months.  Then you get greater-than-normal wind or tornado damage.  It is freezing on winter and 70-degrees for multiple days the next.  We call those rain fall events more 'intense'.  No smooth curve, but choppy up and down across the year.  We hear this on NAT: 'flash drought'.

Dr. Cook has a nifty spreadsheet that puts a best-fit climate model together with some yield work and you can choose your soil and drainage extent and take a stab at the future - the summary is plow your new laterals deep in the black dirt and keep your soil column as empty as possibly so you can absorb the predicted heavy rains without drowning out your crop.



Coefficient of drainage trends:
If you read some old books and look at the designs of old drainage district tile mains (1880s - 1930s) you see a 0.25" DC popping up.  This morphed into 3/8" later and certainly by the 70's.  In the last 15 years discussions from Dr. Cook, UIUC's professor on tile drainage, is to put in 0.5" mains and stick with 3/8" laterals as you get a boost when the fields are saturated (when the water pushes into the tiles 4x as fast as it does when the tile finally drains the water column directly above it at the point where the 3/8" DC is measured.  Now we see the innovators looking at 0.5" systems across the board in field crops and 3/4" or better for vegetable crops.  Golf courses run even higher - as much as 1.5" DC.  Gotta be able to hit the links in the morning (although I find skeet is 1000 times more fun than golf and takes the same or less amount of time).

On our farm, we are installing laterals at around a 0.67" DC where we can get it reasonably (central IL black dirt on 50's) and 3/8" where we can't (clay southern IL dirt that normally isn't tiled anyway).  We want the water gone and the money is there backing my claim.


Surface drainage:
You hit the nail on the head with surface drainage.  Looking at terraforming with OptiSurface and going back to ridges, especially on the lighter clay ground.  Trying to get in the loop on the beds/hippers, I need check in with some of the Delta guys and go look around for a long weekend.  

We are putting basins in places where they are needed and also some places where there is ephemeral erosion where one might normally opt to treat without tillage or with vegetation (cover crops) because any erosion spot just continues to get worse, fast.  I am opting for 25-year return period basis sizes with 12-hour dewatering instead of 10-year basins with 24-hour dewatering.  I don't want them breached, I want them working.  Also looking more at grassed narrow basins because of keeping the berm height for overtopping.  GPS shut-offs make that easier than it used to be.




Lakes are outside my expertise, but I find your information on cycles very interesting.  Do you lose cropland during the high-water cycles and then recover it?  Are there wetland issues?


And as re: anthropogenic effects - I think we know there are some overall effects.  So we collectively are or have been defining the extent of the contribution of various factors.  Then we can decide if we want to change any of those factors.  And even if the overall contribution from humans is small (which I think most work shows the human causes are significant and large), we could choose to have the temerity to attempt to modify the climate anyway - I'm much happier in the 70-degree room than a 73-degree room, and happier on the beach than back in the palm trees around the rocks, so to speak.

In the end, I'm a businessman and I like to grow corn and soybeans and regardless of the causes of any shifts, the shifts are here and likely to be continuing and I'm on the bandwagon of let's understand what is going to happen and figure out how to make money in the likely different environment (no pun intended but pretty good nonetheless) of the future, and eventually at some point figuring out how to make money involves figuring out the causes we skipped over previously in our analysis ...