Saving water with smart irrigation systems

Frank­furt wants to become a pio­neer in water-sav­ing irri­ga­tion of city trees: The city could poten­tial­ly use around a thou­sand cubic meters less water in the future by opti­miz­ing irri­ga­tion process­es for young urban trees. This is the first inter­im result of the “Smart Irri­ga­tion” pilot project, which researchers at the Uni­ver­si­ty of Hohen­heim in Stuttgart are con­duct­ing togeth­er with FES Frank­furter Entsorgungs- und Ser­vice GmbH and oth­er project par­tic­i­pants. An intel­li­gent mea­sur­ing and com­put­er sys­tem records the cur­rent water sup­ply of the trees. In the future, this could enable irri­ga­tion to be demand-ori­ent­ed and dig­i­tal­ly controlled.

In view of the increas­ing­ly hot and dry sum­mers, the issue of water scarci­ty is also becom­ing more and more impor­tant in Ger­many. In large cities in par­tic­u­lar, which already have to cov­er their water require­ments from the sur­round­ing coun­try­side, sealed sur­faces and falling ground­wa­ter lev­els are exac­er­bat­ing the prob­lem. In the sum­mer months, this often leads to a lack of water sup­ply for urban trees with seri­ous con­se­quences. Accord­ing to press reports, sev­er­al thou­sand trees in Ger­man cities die each year from lack of water.

Yet trees are cru­cial to a city’s micro­cli­mate and its air qual­i­ty; not only do they pro­vide shade, increase humid­i­ty, low­er the ambi­ent tem­per­a­ture and fil­ter out dust and pol­lu­tants from the air. They also have a pos­i­tive influ­ence on the human psy­che and con­tribute to the well-being of city dwellers.

Few studies on smart irrigation systems in cities

With cli­mate change, more and more cities are turn­ing to smart city con­cepts that use advanced infor­ma­tion tech­nolo­gies to con­serve scarce resources. Espe­cial­ly with regard to the water sup­ply of urban trees, the instal­la­tion of intel­li­gent irri­ga­tion sys­tems can be use­ful. This is shown by a research project of the Uni­ver­si­ty of Hohen­heim and FES Frank­furter Entsorgungs- und Ser­vice GmbH in coop­er­a­tion with the Frank­furt Green Spaces Office, the Frank­furt Pal­men­garten, IoT Con­cepts GmbH & Co KG, click­bar. GmbH, as well as the Project Group Busi­ness Infor­mat­ics of the Fraun­hofer FIT and the FIM Research Center.

Cur­rent­ly, in the city of Frank­furt, as in many oth­er cities, trees are irri­gat­ed with a fixed amount of water accord­ing to a pre­de­ter­mined sched­ule. Accord­ing to experts, this rigid water­ing sched­ule can lead to over­wa­ter­ing of some species and opens up the poten­tial for water sav­ings. In addi­tion, con­tract­ed ser­vice providers some­times use potable water for com­pet­i­tive rea­sons, even though the city’s Parks Depart­ment pro­vides sev­er­al process and stormwa­ter sources city­wide that could be used for irri­ga­tion ser­vices. In a mod­el project, the research team is work­ing with the city gov­ern­ment, IT spe­cial­ists and botanists to inves­ti­gate how to design a smart irri­ga­tion sys­tem for urban trees.

“A vari­ety of smart irri­ga­tion meth­ods already exist in the agri­cul­tur­al sec­tor. How­ev­er, stud­ies that exam­ine what smart irri­ga­tion sys­tems can look like in urban set­tings are scarce. To our knowl­edge, our study is among the first to pro­pose a design for a smart irri­ga­tion sys­tem for urban trees.”

- Dr. Valerie Graf-Drasch, post­doc­tor­al researcher in the Depart­ment of Dig­i­tal Man­age­ment at the Uni­ver­si­ty of Hohenheim

Intelligent irrigation system will determine water requirements in the future

In order to min­i­mize water loss­es, an intel­li­gent irri­ga­tion sys­tem must deter­mine the water require­ments of the plants as accu­rate­ly as pos­si­ble and ensure an opti­mal water sup­ply. To this end, small mea­sur­ing devices equipped with a trans­mit­ter were insert­ed into the soil of eight young ash trees in the tri­al. This is because fresh­ly plant­ed, young trees are par­tic­u­lar­ly depen­dent on an ade­quate water supply.

Both soil mois­ture sen­sors and ten­siome­ters are used. These record the so-called water poten­tial of the soil. It indi­cates how much water is avail­able to the plants at dif­fer­ent depths and what force the trees need­ed to draw it from the soil.

The data is trans­mit­ted via a spe­cial city-owned radio net­work direct­ly to a cen­tral com­put­er, which in the future will use it to cal­cu­late the indi­vid­ual water­ing require­ments of each tree. The goal is to no longer pro­vide each tree with a pre­de­ter­mined amount of water across the board, but rather to deter­mine the amount need­ed depend­ing on the loca­tion and thus save water. “More research is need­ed before a smart irri­ga­tion sys­tem can auto­mat­i­cal­ly cal­cu­late indi­vid­ual water require­ments from soil para­me­ters and oth­er para­me­ters. Until then, how­ev­er, the col­lect­ed data will in any case help to sup­port human experts,” empha­sizes Flo­ri­an Hawl­itschek, Inno­va­tion Man­ag­er at FES.

The pilot project also con­firms that this can suc­ceed: an ini­tial eval­u­a­tion of the data col­lect­ed shows that the trees stud­ied actu­al­ly had enough water avail­able in April 2021 and were still irri­gat­ed. Accord­ing to the researchers, an opti­mized irri­ga­tion scheme in the spring of this year could have reduced water con­sump­tion in Ger­man cities by sev­er­al mil­lion liters.

Dr. Graf-Drasch points out, how­ev­er, that these pre­lim­i­nary results should be inter­pret­ed with cau­tion. In oth­er years, the results could be dif­fer­ent. “How­ev­er, the results of this test show that a lot of water can be saved in the main­te­nance of urban green spaces. That’s because, con­verse­ly, our sys­tem also allows us to deter­mine whether a tree has received too much water. Espe­cial­ly in times of aggra­vat­ed water scarci­ty, this is an impor­tant find­ing. Dig­i­tal and auto­mat­ed tech­nolo­gies can help us become bet­ter and more effi­cient at pro­tect­ing the envi­ron­ment in the future. How­ev­er, instead of fixed routes and water quan­ti­ties, more flex­i­bil­i­ty will then be required.”