Rewrite Vegetation vigor demonstrates that the Sierra Nevada mountain

image: Researchers who carried out the study

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Credit: Universidad de Córdoba

Vegetation vigor demonstrates that the Sierra Nevada mountain range’s ancient irrigation channels affect soil moisture levels

From satellite images taken over a period of 26 years, a team at the UCO shows how a system of irrigation channels dating back to the Roman Empire increases the water content of the soil adjacent to them

The Sierra Nevada Natural Park is traversed by more than 700 km of channels dug into the earth, through which the water circulates, with a network of irrigation conduits whose splendor peaked during the al-Andalus period. Although their best-known function is to distribute irrigation water, they are also essential for recharging aquifers.

The Sierra Nevada’s irrigation channels are a system for the “sowing” and “harvesting” of water: they allow for the collection and infiltration of meltwater at higher altitudes (sowing) and its subsequent exploitation in lower areas (harvesting), or in the natural springs of local villages.

As it passes through the area, this system modifies soil moisture levels. To evaluate the scope of their area of influence, researchers Javier Aparicio, Rafael Pimentel and María José Polo, with the Fluvial Dynamics and Hydrology group; and Francisco Bonet, in Terrestrial Ecology at the University of Córdoba, used the vigor of vegetation as an indicator of the water content of the soil in areas stretching more than 200 meters around the channels. Through satellite images from the period from 1984 to 2020, part of them processed within the ECOPOTENTIAL project, they analyzed the vigor of the surrounding vegetation, using the Normalized Difference Vegetation Index (NDVI), which evaluates the health and density of vegetation based on these satellite images. 

“To see how far the channel modifies soil moisture transversely,” explained researcher Javier Aparicio. Three zones of influence were defined around the channels, without distinguishing between the margins, due to the similarity of the slopes. Zone Al-1 covered up to 50 m on each side of the channel, Al-2 extended from 50 to 200 m, and Al – 3 included areas over 200 m. After the comparative study of the NDVI index in each of the areas with monthly data, it was clear that, the closer to the ditch, the higher the figures were, but the surprising thing was that in Area 2 (from 50 to 200 meters) the numbers were also high, suggesting that the channels´ effects surpassed the 50 meters nearest to them.”

The study reveals a seasonal pattern in the vegetation vigor data “with a direct relationship between the hydrological dynamics of the basin and how well the vegetation does, which is more accentuated in the area closest to the channels,” added researcher Rafael Pimentel.

Channel restoration works

In addition to this general study, which includes 45 of the Sierra Nevada’s channels (the longest, distributed throughout the northern and southern territory), the team carried out more specific work focused on the Barjas Channel, restored in 2014 by the MEMOLA project at the University of Granada.

In that study, they found that after restoration, NDVI values increased by 19%, with a greater increase in the lower part of the channel, which the  course did not reach adequately prior to its restoration.

The study of these very specific infrastructures in such emblematic places is somewhat rare, which meant that the team had to employ an analysis methodology more commonly applied to rivers and other larger systems. “The methodology can be extrapolated to other similar traditional systems, such as those found in Morocco’s Atlas Mountains,” Aparicio added.

This work highlights those traditional water management systems in remote areas where technification is  very complex, but which continue to generate value for the population and the environment.

Reference:

Aparicio Ibañez, Javier & Pimentel, Rafael & Bonet-García, Francisco & Polo, Maria. (2025). Using NDVI-derived vegetation vigour as a proxy for soil water content in Mediterranean-mountain traditional water management systems: Seasonal variability and restoration impacts. Ecological Indicators. 174. 113468.