A few weeks ago, I couldn't get electricity into the ground.

Let me explain…

By training, I'm a hydrogeologist, and over the last year or so, the work kind of found me without me actively searching for it. Croatia is in a drought, and since I partnered with my college colleagues on helping people find water underground, my inbox is full of people asking us to find water for their wells.

So we've been out in the field all across the country. Part of what we do is geophysics: we push an electrical current into the ground through metal electrodes and read how it travels through the layers below. Different rocks and structures have different electrical readings, so that's how we identify where water could be underground.

And that's where it got a little surprising recently. We were in the continental part of Croatia, the green part with deep soils, and we couldn't do our survey properly. The issue was that the current wouldn't go deep enough because the soil underneath was too dry to carry it, which is kind of crazy to be experiencing in October.

Looking from a distance, it all looks fine, and most people driving past that field would see green grass and no issues. But our instruments were telling a different story, and up close, we could also see the soil crust cracking across the field.

We’ve had a shower here and there since late August, but to hydrate the soil and get back on track now, we would need continuous rain for weeks, not minutes. So we are already coming into winter in a severe water deficit, and even if we get normal winter precipitation (which is highly unlikely, since there is no snow like it used to be), we’ll still have a shortfall for the coming spring. And this keeps on happening year on year.

I feel like we are on the precipice of a water disaster, and because I'm so close to the water-table exploration work, I’m the first to know. The drought trend is obvious and has only been accelerating in recent years.

Croatia isn't the only one battling this. The EU's latest drought bulletin puts a water-deficit alert over a big chunk of Europe. The latest report even indicates that in the Alps, the snow now lasts about 36 days less than its 600-year average. Less snow, less melt, less water in rivers, less water underground for vast stretches of the continent.

Everyone's answer to this is the same: go deeper to get the water. But only a few can afford this, since drilling and deep boreholes can cost a lot of money.

Most people will rely only on rainfall because your trees can't ‘drill’ deep enough to reach the receding water table.

Where the roots actually are

You might have heard that trees send a taproot down to find water when it gets dry. But in reality, most don't.

Most mature trees don't have a taproot at all, and nursery trees lose theirs before you ever plant them! Some species, like certain oaks and pines, keep a few deep roots, but they grow those in good years, in moist soil. They don't send them down in an emergency.

Over 90% of a tree's root mass actually sits in the top 45 cm (18 in) of soil, and about half of that in the top 15 cm (6 in). Sideways, feeding roots reach past the dripline (the edge of the canopy, where the outermost branches end), often out to about 1.5 times the canopy width, farther in sandy soil and less in heavy clay.

The thing is, roots won’t tunnel through dry soil looking for water. They will grow where water and air already are, and when the soil dries out, the fine roots simply die back or go dormant and wait.

The real question is then whether whatever water is available reaches where those roots already live. This is the key to tree survival in drought!

In essence, I recommend three ways to prioritize this, and here's how I'd rank them.

1. Catch more rain and give it to the tree

This is the best option because it works while you sleep.

Swales, basins, half-moons, and berms collect the runoff from a bigger area and sink it into the root zone.

Here's the math. Say the basin around a tree catches the runoff from 20 m² (215 sq ft) of ground. The same 10 mm (0.4 in) of rain could deliver around 200 L (53 gal), instead of 70 L (18 gal), that the tree would get on its own from rain falling only on its root zone.

Now, to be honest, in a light shower on dry ground you won't get that much, because the ground soaks up those first millimeters before anything flows. Still, earthworks pay off, especially in big storms when water would otherwise run off your land.

2. Irrigate from storage, properly and at scale

This is second best, and it needs some planning. Here you’ll need to dig/build a water storage system you can use to irrigate when you need it. The key is that it has to be big enough to supply enough water.

Say you have 20 young trees. Each one will need about 280 L (74 gal) to wet its root zone to 30 cm (12 in), so watering all 20 trees deeply just once takes about 5,600 L (1,480 gal). In a dry spell, you'll need to repeat that every week or two.

So 5 m³ (1,320 gal) every two weeks for a two-month drought is 20 m³ (5,300 gal). That is not much storage (5 m wide, 4 m long, 1 m deep, or roughly 16 × 13 × 3 ft), but we are talking 20 young trees only, so size your storage accordingly.

When irrigating, deliver the water slowly at the dripline, not at the trunk. A ring of drip line around each tree on a timer works well here. If you can put the storage higher than the trees, gravity does the delivery for free.

3. Hand watering, done properly

This is the stopgap. If you have no well and no rainwater harvesting storage, use municipality-supplied water and water by hand.

You’ll spend a while watering the trees here, though. As in the example above, water in a ring under and just outside the canopy. as I said, most feeding roots are farther out.

Aim at about 280 L (74 gal) for a 2 m-canopy (6.5 ft) tree in loam (adjust for your soil). At a garden-hose watering rate, you’ll need about 20 minutes per tree! Told ya you’ll be there a while.

In drought, you’ll need to do it every two weeks, so that really adds up in maintenance time. Still, it’s an option if you don’t want to lose your trees.

Now, established, mature trees can withstand drought. You don’t need to be evangelical about watering them like newly planted/young trees. Still, no trees will grow without water, and without it you’ll lose out on growth and production. So anything you can do to supply the water helps.

All right, hopefully this was insightful! Now, hit reply and let me know: which of these three are you using to get water to your trees right now? Or perhaps you are doing nothing at all. No judgment, just let me know.

I read every reply.

Talk soon,

-William