Finding new ways to keep the land alive
Studying precipitation changes helps us understand future impacts on NM’s water resources
El agua es vida. Water is life. This concept is universal, but it is particularly applicable in the dry, arid climate of northern New Mexico.
When people think about water in this area, acequias might immediately come to mind. They are an important part of New Mexico history and have been providing water to crops dating back to Native peoples in the 1400s. Year in and year out, the complex irrigation systems literally brought life to people in northern New Mexico.
But water does not just play an important role in agriculture; water resources are also vital to a variety of ecological, municipal, industrial, recreational and societal needs across the region. On a local level, water from the headwaters of the Pajarito Plateau in the Jemez Mountains eventually finds its way down to the Rio Grande, which supplies water to surrounding areas, and then continues downstream to supply water to Texas and eventually Mexico.
Because of the dry climate and steep terrain in northern New Mexico, the amount of water available to its communities is driven largely by winters with heavy snowfall and summer monsoons. Historically in the upper Rio Grande, most of the water flow for the basin comes from high-elevation snowpack that begins in October or November and melts by June. Monsoonal rains usually begin in June and last until September, providing more than half of the incoming precipitation to the region.
However, as average temperatures rise, as Earth system models predict, communities that rely on surface water, such as Santa Fe and Albuquerque, and farmers throughout the region could face challenges in the future. Snowpack usually melts slowly throughout the spring and allows water to be absorbed into the ground, rather than becoming runoff. The same can be said for the heavy, but short, bursts of rain during the summer. With temperatures expected to rise by somewhere between three and seven degrees by 2050, the amount of precipitation and its form may change, making the water less available for people to use.
Higher temperatures could mean that there will be more rain throughout the year and less snow. As a result, more of the precipitation could become runoff, never being absorbed by the land; smaller snowpacks that melt faster will amplify this problem.
Heavier rainfall and snow packs that melt faster present a unique problem: water is introduced too quickly and never has a chance to be absorbed. This runoff finds its way to streams and rivers, and continues downstream as part of the natural water cycle. When snow melts more slowly and rain falls at a slower rate, it gives the ground a chance to absorb the moisture. That replenishes the ground water that communities rely on and can create a water reserve that can be used in drier times.
Changes in snow, rain, and drought across the region will affect cities, operations and resources that rely on a consistent water source. Communities need to understand these changes and their impact so planners can prepare for times with less water. To help, a team of researchers at Los Alamos National Laboratory is using computers to model how the land is impacted by changes in temperature and precipitation, taking into account elevation, soil data, geology, vegetation and other factors. Their research shows how much rain or snowmelt is absorbed, how much becomes runoff and how that affects surface-water levels.
The team’s recent study showed that changes in absorption and runoff have a significant impact on water quality and quantity in the region. They also found that absorption and runoff are sensitive to changes in seasonal precipitation — when it rains, when it snows and if some precipitation falls as rain instead of snow because of warming temperatures.
It turns out that the form and rate of precipitation might be more important than the overall amount. If precipitation that might have fallen as snow in March in previous years shifts to March rains in the future, much of that water might drain off the mountains into the river at a time when irrigators cannot use it, for instance. Increased rainfall can lead to increased erosion, causing increases in sedimentation, which has negative impacts on water quality, alters habitats and washes away soil, which then limits plant growth.
All these threats pose unique challenges, but using models to study the risks can help communities prepare for them. Knowing if vegetation is drier and more susceptible to fire can help land managers prepare for, or prevent, fire conditions. Understanding how water movement is changing across the landscape can help to determine value and risk in development of land. And knowing that, with warmer temperatures, snow may not provide the reserve it has in the past can help guide water managers in conserving and protecting water resources.
With this knowledge, during times of drought in the future, the communities in northern New Mexico can understand why there is less water, keep the acequias flowing and find new ways to keep the land alive.
Katrina Bennett is a hydrologist at Los Alamos National Laboratory. She studies changes to water resources that impact human and ecological systems. Her research has focused on the influences of climate variability on the hydrology of watersheds in the Colorado River basin, Rio Grande, Alaska and Canada.