Using Technology and Old Photos to Map Erosion in Jaén's Olive Groves

A new method for ana­lyz­ing soil ero­sion and its impact on olive groves has been devel­oped by the researchers at the University of Jaén.

A bet­ter under­stand­ing of how the groves’ soil changes over time – its com­po­si­tion, vol­ume, shape and other char­ac­ter­is­tics – may offer grow­ers a new set of tools to plan their oper­a­tions.

The team, from the uni­ver­si­ty’s cen­ter for advanced stud­ies of Earth sci­ences, energy and envi­ron­ment, stud­ied aer­ial pho­tographs taken over sev­eral decades to eval­u­ate the chang­ing soil con­di­tions of the olive groves. 

“The aer­ial pho­tographs col­lected either by con­ven­tional air­craft plat­forms or drones were cou­pled with LiDAR (Laser imag­ing detec­tion and rang­ing) data to make dig­i­tal sur­face mod­els,” Tomás Fernández, one of the authors of the study, told Olive Oil Times.

He added that these dig­i­tal ele­va­tion mod­els (DEMs), ​“are accu­rate rep­re­sen­ta­tions of the ground heights.”

By com­par­ing DEMs obtained from decades of aer­ial pho­tographs and LiDAR, a whole new set of data was cre­ated 

“In Spain, we’ve had peri­od­i­cal aer­ial flights over the ter­ri­tory since 1956. Since 2004, this has hap­pened every two or three years, and drone flights can be oper­ated when needed,” Fernández said.

“Therefore, we could com­pare DEMs from dif­fer­ent dates and the result of this com­par­i­son, the dif­fer­en­tial DEMs, allows us to iden­tify areas in which the ground sur­face decreases – the ero­sion areas – and loca­tions where the ground sur­face increases – the depo­si­tion areas,” he added.

By quan­ti­fy­ing these areas and the ero­sion or depo­si­tion heights asso­ci­ated with them, researchers were able to eval­u­ate the vol­umes of mate­r­ial involved in the chang­ing soil shapes.

“We have cal­cu­lated an increase of two inches per year in some sec­tors of the gul­lies from 1984 to present, and soil losses of 50 tons per year for every 2.5 acres, almost twice the esti­mated annual aver­age losses in the province of Jaén,” Fernández said.

The researchers also deter­mined that dur­ing peak peri­ods, when soil ero­sion accel­er­ated, such as from 2009 to 2010, the rate of ero­sion reached 20 inches per year with a total loss of 450 tons per year for every 2.5 acres, a ten­fold increase when com­pared to the aver­age losses that were esti­mated by experts and farm­ers before this study was com­pleted. 

“Those are val­ues to be taken into account because they cause very sig­nif­i­cant losses of fer­tile soil, as well as very sig­nif­i­cant dam­age to crops and infra­struc­ture,” Fernández said.

Researchers also found a cor­re­la­tion between soil ero­sion in olive groves and peri­ods of increased rain­fall – a find­ing with a twist.

The researchers noted that soil ero­sion in peri­ods of heavy rain­fall had a more notice­able impact in recent years, such as from 2009 to 2013, when com­pared to sim­i­lar rain­fall pat­terns from ear­lier time peri­ods, such as from 1996 to 1998.

“Considering these find­ings, we sus­pect that an accel­er­a­tion in the soil ero­sion process is on its way, prob­a­bly due to the effects of infra­struc­ture, dif­fer­ent poli­cies in the man­ag­ing of the ter­ri­tory as well as the chang­ing rain­fall,” Fernández said.

While the study was con­ducted in a spe­cific olive oil pro­duc­ing region, the method devised by the researchers can be applied to other rel­e­vant ter­ri­to­ries as well.

“The tech­nique can poten­tially be applied every­where, at least where aer­ial pho­tog­ra­phy of the ter­ri­tory and LiDAR data can be made avail­able,” Fernández said. ​“Should these data not be avail­able, a his­tor­i­cal inves­ti­ga­tion is not pos­si­ble.”

“Still, actual and future evo­lu­tion in the soil ero­sion can be addressed by means of drone flights or ter­res­trial pho­togram­me­try and LiDAR,” he added.

Their study could help bet­ter under­stand what the researchers believe is a ​“cur­rent major prob­lem at the global level, which has a rel­e­vant impact in Mediterranean coun­tries and, locally, in the olive groves of Jaén.”

A prob­lem, they said, ​“which may crit­i­cally increase in the com­ing years.”

• International Journal of Geo-Information
• University of Jaén