Zuni, N.M.
There were times last fall when I would swear I was driving through Scotland. If I squinted at the distant landscape, the green hills without trees looked like the highlands of the northern British Isles. After a summer of glorious rain, western New Mexico had leafed, bloomed and grown like it hadn’t in decades. Rivers ran and stock ponds filled. Wildflowers that hadn’t appeared in years sprang up.
Surely the drought that had gripped the Southwest for most of the last 10 years was over – or was it? As a friend remarked, we are as optimistic as the last downpour.
Measuring a drought is surprisingly difficult; it depends on whom you ask and how you choose to measure. In addition to how much rain falls, timing is equally important. If our annual 12 inches fell in a single week, it would be a disaster. The split between winter and summer rains is crucial, as the slow-melting snowpack does more to replenish groundwater than intense but fleeting thunderstorms. When you take into account soil moisture, groundwater, stream and lake levels, vegetation growth, humidity, temperature, and the difference from state to state, or even watershed to watershed, it gets really complicated.
There are no fewer than seven drought indices in use today. Percent of normal precipitation (the one you see in the newspaper) measures rain and snowfall starting on Jan. 1, and compares it to the long-term cumulative average for the current date. It’s a flawed measure in that it begins in the middle of the winter wet period, and it doesn’t take into account long-term trends. The other indices also have limitations, so a recent trend has been to incorporate measurements of atmospheric humidity – how much moisture the air is holding and how quickly it’s evaporating – in recognition that moisture loss is as important as moisture gain.
Much of the difficulty in calling a drought – or its end – centers on the larger question of what is “normal” precipitation. It’s an echo of the global warming debate, as scientists struggle to define normal temperature as well as deviations from it. Earth, of course, is a sample size of one, with no “control planet” for comparison. This presents a challenge in drawing statistically firm conclusions until the results begin to shout loudly, as they are now doing.
Despite what we know about the need for long-term observations, we almost always make land management choices based on short-term knowledge. Water allocations for the Colorado River Basin are a famous example, since they were set during a period of heavy rainfall in the early part of the last century. When precipitation returned to modest levels in the 1930s and ’40s, it became clear that the river had been over-allocated.
On the ground, at least, in New Mexico, things looked great last summer as the vegetation shot up faster than the cows and the elk could mow it down. Before livestock grazing became an economic force in the Southwest, early settlers remarked that grass grew “up to the bellies of the horses.”
A cynical range manager I know remarked, “Sure, but that was all dropseed and sleepy grass” – or in other words, non-palatable, weedy grasses. I had read how frequent but relatively “cool” grass fires kept piñon and juniper trees relegated to rocky hillsides, but I’d never understood how flames could carry across the scrawny, ankle-high grass of the Colorado Plateau. Then came last summer, and as seed-heads grew lush and grasses grew most definitely high as a horse’s belly, a juniper-killing prairie fire became easy to picture.
The heavy rains were a blessing and a curse. It was a blessing that my daughter and I could birdwatch in the re-wetted marsh near our home. It didn’t get deep enough for diving ducks and a colony of eared grebes to return from their decade-long sabbatical, though a handful of coots and mallards found it welcoming enough. But the rain was a curse in that, if this year’s cycle was a brief aberration, no one is going to listen to a hydrologist shouting “drought” while they’re shoveling a truck out of the mud.
Recently, while out doing fieldwork on a chilly and stormy morning, my colleagues and I we were trying to decide if it was worth heading into the field. I mentioned that the forecast called for the weather to improve later in the day – which, a friend in the group remarked, meant more rain.
Steven Albert is a hydrologist in Zuni, N.M., and is a contributor to Writers on the Range, a service of High Country News (hcn.org) in Paonia.
