Drought on the Lower Rio Grande: groundwater keeps pecan trees healthy, at a price

Despite another dry year, the pecan trees in New Mexico’s Mesilla Valley are healthy, and the reason is under the ground. This Climate.gov article is the second of a two-part series on the drought in the Lower Rio Grande Valley; part one covered changes in water supply and how regional water managers are responding. This part looks at the cost to farmers.

By the end of September, nearly all the surface water in the Lower Rio Grande had been drained. Below Elephant Butte Reservoir the river ran as a trickle, with sandy bars exposed where it had been flowing as recently as mid-September. At Greg Daviet’s pecan farm outside Las Cruces, groundwater pumps droned and wells spilled clear water onto the orchards. It was the ninth time in the last decade that farmers received only a fraction of the surface water they need.

Pecan trees near Hatch, New Mexico, soaked with irrigation water from wells. Image from Climate.gov’s page.

Why surface water ran short

Back-to-back La Niña events in the winters of 2010 and 2011 helped steer storms away from the Upper Rio Grande Basin in Colorado, where most of the river’s water originates. Rain and snow totaled less than 82 percent of the 1971–2000 average in those winters. Reservoir storage has been on a decreasing trend since around 1999. As of September 1, Elephant Butte, the region’s largest reservoir, held less than 5 percent of its capacity, and the water the Elephant Butte Irrigation District had available for future irrigation was completely used up. From here on, the surface water farmers get will depend on the previous winter’s precipitation and will probably fall short of demand, so irrigators will keep relying heavily on groundwater.

The aquifer as a shield

Under the river, porous sediments form a second, larger reservoir. The aquifer beneath the Mesilla Valley is more than 2,000 feet thick in some places, according to recent hydrogeological studies. Phil King, a professor of civil engineering at New Mexico State University and a consultant to the irrigation district, describes surface water and groundwater as one closely linked system: the aquifer recharges when surface water is plentiful, and in drought farmers withdraw from it, to be paid back by later surface supplies. Groundwater also lets farmers water on demand, which matters because in midsummer the district can deliver only a fraction of the water needed and some farmers have to wait.

Daviet’s water table has dropped only 30 feet in 10 years of drought, and his wells go more than 300 feet down, so he is not worried about running out. About 40 miles north, near Hatch, the aquifer is much smaller and water lies less than 200 feet down. Rosie Lack of Lack Farms, which grows onions, chili, cotton and other crops on about 1,500 acres, says most of the farm’s wells are 60 feet deep. As the water table falls, it dips below the pumps’ intake valves when pumping is ramped up, so water and air are drawn together and the flow drops. She does not think the farm could last more than five years if low surface-water allocations continue.

The Rio Grande provides irrigation water in southern New Mexico’s otherwise arid landscape. When surface water dries up, growers near Hatch, where the aquifer is shallower, have a harder time tapping groundwater than growers near Las Cruces, where it is deeper. Photo courtesy of the NASA JSC Gateway to Astronaut Photography of the Earth.

What it costs

Pumping is not free. Groundwater costs more per acre-foot than surface water, and it is saltier. Daviet says that when he has to pump nearly all of his water, it adds 10 to 15 percent to a pecan farmer’s normal expenses. Big capital improvements make it worse and come more often in dry years. He needs to flood his fields at about 2,500 gallons per minute, but this year could pump only 1,900 after one well failed and lower water tables cut the output of the other two. Each 10 feet the water table drops costs him about 100 gallons per minute. A new well cost $150,000, a big part of his operating budget; he says such improvements can reach 30 to 40 percent of an annual budget in years when pumping has to be upgraded, and for a marginal farm that could be the last straw.

Costs reach beyond pecans. In Hatch, the article says, the chili pepper is king, and Jim Lytle’s family has farmed the valley since the late 1800s and helped pioneer chili production there. Lytle says an acre of chili takes about four feet of water, and with the surface allocation so small the rest has to be pumped. He expects to make probably half of what he normally makes. Lack says the drought has probably cut yield potential by at least 40 percent while raising expenses.

Young chili peppers in a field near Hatch, New Mexico, in early July 2012. Image from Climate.gov’s page.

Salty soils

Groundwater has hidden costs too. The local deposits are rich in salts and minerals, and groundwater, which spends a long time in contact with them, picks them up much as hot water extracts caffeine from coffee or tea. Daviet says those minerals and salts can harm the trees. Drought makes this worse: more pumping lowers the water table, so pumps draw from the upper part of the aquifer where salinity is highest and from its fringes, where salts concentrate. The longer and harder wells are pumped, the saltier the water and eventually the soil, especially near Hatch. Lack, in her fourth year of limited river water, describes fighting sodium in the soil, ground that feels like stepping on crackers.

Salinity is best fought with surface water, which is scarce in a drought. New coping strategies, including more coordinated management, can help. Daviet, for example, can sell his surface-water allocation to farms in Hatch in return for compensation for the added cost of pumping more groundwater, and leasing water within an established water market directs limited surface supplies to areas where groundwater is harder to reach. His view is that drought is not the end of the world and that farmers adjust to it as long as they do not fight change.

Sources

• NOAA Climate.gov, “The Costs of Drought on the Rio Grande,” https://www.climate.gov/news-features/features/costs-drought-rio-grande; rewritten in hubnx's own words. The farmers’ and professor’s quotations are paraphrased.