The Sacramento Mountains Watershed Study: Can Thinning Trees Increase the Water Supply?

Water is the limiting resource in New Mexico. Demand for this resource is primarily driven by population growth and agriculture, while supply is mainly driven by climate. Rain and snow in the high mountains feed streams and recharges local and regional aquifer systems. As the population continues to grow and under the pressures of climate change, water demand in New Mexico is going to increase while the water supply may actually decrease. While conservation practices are necessary to manage New Mexico’s water demands and uses, there may be ways of increasing the water supply. Thinning trees in mountainous areas, which improves wildlife habitat and reduces fire danger, may also have implications for increasing the groundwater and surface water supply. Much research over the last 50 years shows potential for tree thinning to increase water yield. However, hydrologic responses to thinning trees are highly variable and site specific. The New Mexico Bureau of Geology and Mineral Resources conducted the Sacramento Mountains Watershed Study, which took place in a high-elevation watershed in the Sacramento Mountains in southern New Mexico. This study, which focuses on assessing the effects of tree thinning on the local hydrologic system, analyzes each component of the soil water balance and how it responds to removing trees in the forest. More water reaches the ground due to a decrease in canopy interception. Surface runoff was not affected by the treatment. Net evapotranspiration (ET) does decrease when trees are thinned. However, soil water evaporation also increases. Results indicate that thinning trees may potentially increase local groundwater recharge. However, the complexity of the karstic aquifer system in the area makes it difficult to determine the magnitude of this increase in water supply.