How Turf Alert knows when your US lawn needs water

"It hasn't rained in a while" isn't a threshold — a dry week in a wet month and a dry week in a genuine drought look identical on a rain gauge. Turf Alert tracks something more useful: a running soil moisture deficit (SMD), rainfall in and evapotranspiration out, the same water-balance accounting agronomists use.

The 60mm line

Once a lawn's accumulated deficit crosses 60mm, the watering trigger fires. From there, the alert stream keeps pace with how the drought actually develops, not just whether it's still going: a fresh alert whenever the deficit deepens by another full 60mm (real escalation, not noise), and a periodic check-in if the deficit plateaus painfully high without clearing — the same kind of long, dry stretch that once produced a single alert on day one while the underlying deficit kept climbing for months. Both responses trace back to the same accumulated number, not separate rules bolted on.

Checked against real droughts, not tuned to sound right

The way to know a water-balance model is actually tracking reality, not just producing plausible-looking numbers, is to check it against events nobody told it about. Ranking every backtest year across all 12 covered US cities purely by the model's own deficit numbers surfaces five real, named US droughts — the 1961-1966 Northeast drought, the 1950s Midwest drought, 1988-1990, the 2012 drought, and the 2015 Pacific Northwest snow drought — every one of them found from soil physics alone, never from a list of years to look for. See 5 real US droughts, reconstructed from nothing but soil physics for the full breakdown.

What this means for your lawn

Once your deficit crosses 60mm, it's time for deeper, less frequent watering — or, if you're comfortable with it, letting a cool-season lawn go dormant rather than fighting evaporation you can't out-water. If the deficit keeps climbing after that, you're in a genuinely worsening drought, not just a dry spell that's crossed a line once and settled there — and that's exactly the distinction the escalation alerts exist to make clear.

Check your own city's current deficit on the forecast page, or sign up to get the alert automatically, escalation included.