Vrednotenje vpliva dreves na površinski odtok v urbanem okolju : doktorska disertacija

Alivio, Mark Bryan (author), Bezak, Nejc (mentor), Šraj, Mojca (comentor), Atanasova, Nataša (member of the commission for defense), Zupanc, Vesna (member of the commission for defense), Raška, Pavel (member of the commission for defense)

Urban stormwater management is increasingly challenged by the compounded impacts of expanding impervious surfaces and the rising frequency of localized heavy rainfall events. In response, cities are placing greater emphasis on enhancing and regenerating the capacity of urban landscapes by incorporating naturebased solutions (NbS). For cities to fully embrace trees as a strategic component of Nbs for stormwater management, there is a need for scientific evidence and a comprehensive understanding of their hydrological functions across different geographic settings, urban landscape configurations, and climates. Additionally, current stormwater models often lack the capability to simulate urban tree’s ecosystem services, particularly the stormwater runoff reduction. Hence, the dissertation aims to evaluate the impacts of open-grown birch (Betula pendula Roth.) and pine (Pinus nigra Arnold) trees on urban stormwater runoff. Targeted field measurements were conducted at an experimental urban plot to investigate the effects of species-specific interception processes on drop size distribution (DSD) changes, kinetic energy reduction, rainfall intensity attenuation, throughfall partitioning (free throughfall/FR, splash/SP, canopy drip/CD), and sub-canopy hydrological processes, including the effects on soil moisture and infiltration. Leveraging experimental measurements to obtain species/site-specific input parameters, the stormwater runoff reduction potential of birch and pine trees was modelled using the improved SWMM model with the added canopy module. Owing to rainfall interception, there is a shift in the DSD of throughfall toward larger drop diameters compared to open rainfall while also increasing the presence of smaller drop sizes. Birch, with its broad leaves, facilitates drop fragmentation and coalescence, inducing a change in throughfall DSD with peaks at smaller and larger drop sizes. The needle-like foliage of pine promotes drop coalescence, resulting in fewer but larger drops. Both species increased throughfall D50 by 8.5–26.5% (pine) and 11.7% (leafed birch), with a 5.9% reduction observed in leafless birch. This can be explained by the significant differences in the proportions of each throughfall component between tree species and phenoseasons. SP constitute over 60% of throughfall drop numbers for both species, while CD dominates throughfall volume (40% in leafed birch, > 69% in pine), except in leafless birch where FR predominates (41.8%). Both trees alter the fall velocities of raindrops, with the birch reducing the mean velocity of rainfall by 3.4% and more substantially under the pine at 42.1%. The interception effect extends beyond individual drops, with birch and pine trees reducing the rainfall kinetic energy available for soil detachment and erosion by 21.5–28.5% and 74.9– 85.3%, respectively. The birch and pine canopies further attenuate the mean event rainfall intensity by 33.9– 37.7% and 82.9–85.4%, respectively, which is crucial for regulating the distribution and delivery of rainwater to the ground to infiltrate and/or runoff. The gradual and slow release of CD under the pine leads to a more substantial reduction in KE and intensity. Local microclimatic factors such as vapor pressure deficit, temperature, and humidity further modulate the effect of the rainfall interception process on intensity attenuation and kinetic energy dissipation. These canopy-mediated processes significantly influence both the moisture response and infiltration of soil beneath the trees. Soil infiltration rates were highest in the open area (5.97 cm/hr) followed by that under the pine (5.55 cm/hr) and lowest under the birch (3.76 cm/hr). The soil under the birch exhibited a faster and higher moisture response, especially at 16 cm depth, driven by a higher volume of FR, SP, and increased throughfall intensity. Conversely, the lower throughfall volume, intensity, and more gradual delivery of CD under the pine resulted in slower increases in soil moisture. This is further substantiated by the statistically significant lagged correlations between throughfall components and soil moisture, which show that soil moisture under the birch responds more quickly and directly to SP and FR inputs, whereas under the pine, the gradual release of CD leads to a delayed and prolonged moisture response. Additionally, seasonal changes in LAI have a stronger influence on the soil moisture dynamics below the birch than pine. The application of SWMM canopy module accurately and explicitly simulated the canopy hydrological processes in both trees. This improved the representation of rainfall interception in the model. Results demonstrated that the module’s interception routine effectively captured the temporal evolution of throughfall and stemflow (Tf + Sf) under the birch and pine trees in different phenoseasons. Strong correlations were observed between the simulated and observed Tf + Sf (r = 0.97–0.99) and interception values (r = 0.72) across all storm events. The findings further indicate that implementing birch and pine trees in the study area reduces the runoff volume by 20–25% and peak flow by 16–25% across different scenarios and phenoseasons. The mixed-species tree planting scenario (Scen3 with 50% birch and 50% pine) generally achieves greater reduction benefits in both runoff volume and peak flow compared to the single-species scenarios (Scen1 with only birch and Scen2 with only pine). Analysis of the water balance from the model further emphasizes the relative contribution of canopy interception (up to 21.1%) to the stormwater reduction of birch and pine, particularly during the leafed season, small to moderate storm events, and when trees are planted over directly connected impervious areas. Moreover, infiltration + storage in the soil beneath tree canopies account for more than 20% of the water balance, especially during the leafless season and depending on the soil medium. Overall, the findings of this dissertation highlight that the ability of urban trees to manage stormwater depends on both canopy and sub-canopy level processes. To ensure that their hydrological benefits are properly credited, it is essential to comprehensively incorporate both canopy (i.e., rainfall interception, evapotranspiration) and soil hydrological processes in the analysis and modelling.

• Language: English
• Keywords: built environment, doctoral dissertation, birch, pine, rainfall interception, stormwater, throughfall partitioning, nature-based solutions, soil moisture, infiltration, SWMM canopy module, urban trees
• Work type: Doctoral dissertation
• Typology: 2.08 - Doctoral Dissertation
• Organization: FGG - Faculty of Civil and Geodetic Engineering
• Place of publishing: Ljubljana
• Publisher: [M. B. Alivio]
• Year: 2025
• Number of pages: XXII, 106 str., [73] str. pril.
• PID: 20.500.12556/RUL-175552
• UDC: 556.164:633/635.055:711.4(043.3)
• COBISS.SI-ID: 256010243
• Publication date in RUL: 04.11.2025

Secondary language

• Language: Slovenian
• Title: Evaluating the impact of trees on urban stormwater runoff : doctoral dissertation

Abstract

Upravljanje padavinskih voda v mestih je vse večji izziv zaradi urbanizacije in vse pogostejših lokalnih močnih padavin. V odgovor na to mesta dajejo večji poudarek povečanju in obnovi zmogljivosti mestnih krajin z vključevanjem rešitev, ki temeljijo na naravi (ang. Nature-based solutions ali NbS). Da bi mesta lahko v celoti sprejela drevesa kot strateško komponento NbS za upravljanje padavinskih voda, so potrebni znanstveni dokazi in celovito razumevanje njihovih hidroloških funkcij v različnih geografskih okoljih, konfiguracijah mestnih krajin in podnebjih. Poleg tega sedanji modeli površinskega odtoka pogosto nimajo možnosti simuliranja ekosistemskih storitev mestnih dreves. Zato je namen disertacije oceniti vplive breze (Betula pendula Roth.) in bora (Pinus nigra Arnold) na površinski odtok v urbanem okolju. Ciljne terenske meritve so bile izvedene na poskusni urbani površini, da bi raziskali učinke procesov prestrezanja padavin na spremembe porazdelitve velikosti dežnih kapljic (DSD), zmanjšanje kinetične energije, zmanjšanje intenzitete padavin, porazdelitev prepuščenih padavin (neposredne prepuščene padavine/FR, razpršeni del prepuščenih padavin/SP, kapljanje s krošnje/CD) in hidrološke procese pod krošnjo, vključno z učinki na vlažnost tal in infiltracijo. S pomočjo eksperimentalnih meritev smo pridobili vhodne podatke in določili parametre značilne za vrsto/območje, in jih uporabili za modeliranje potenciala breze in bora za zmanjšanje površinskega odtoka z izboljšanim modelom SWMM z dodanim modulom krošenj. Zaradi prestrezanja padavin se pojavi sprememba v DSD prepuščenih padavin, in sicer povečan premer kapljic v primerjavi s padavinami na prostem, hkrati pa se povečuje prisotnost manjših kapljic . Breza s svojimi širokimi listi pospešuje drobljenje in koalescenco kapljic, kar povzroča spremembo v DSD prepuščenih padavin . Iglice bora spodbujajo koalescenco kapljic, zaradi česar je kapljic manj, vendar so te večje. Pri obeh vrstah so je D50 prepuščenih padavin povečal za 8,5-26,5 % (bor) in 11,7 % (breza v fazi vegetacije), pri brezi v fazi mirovanja pa je bilo opaziti 5,9 % zmanjšanje. To je mogoče razložiti s precejšnjimi razlikami v deležih posamezne komponente prepuščenih padavin med drevesnimi vrstami in fenološkimi obdobji. SP predstavljajo več kot 60 % celotnih prepuščenih padavin pri obeh vrstah dreves, medtem ko CD prevladuje v količini prepuščenih padavin (40 % pri brezi v fazi vegetacije, > 69 % pri boru), razen pri brezi v fazi mirovanja, kjer prevladuje FR (41,8 %). Obe drevesni vrsti spremenita hitrost padanja dežnih kapljic, pri čemer breza zmanjša povprečno hitrost padavin za 3,4 %, bor pa bistveno bolj, in sicer za 42,1 %. Učinek prestrezanjapadavin zmanjša kinetično energijo za 21,5–28,5 % (breza) oziroma 74,9– 85,3 % (bor). Krošnje breze in bora dodatno zmanjšajo povprečno intenziteto padavin za 33,9–37,7 % oziroma 82,9–85,4 %, kar je ključno za uravnavanje porazdelitve in odtoka padavinske vode ter infiltracijo. Postopno in počasno sproščanje CD pod borovci vodi k znatnejšemu zmanjšanju KE in intenzitete. Lokalni mikroklimatski dejavniki, kot so primanjkljaj vodne pare, temperatura in vlažnost, dodatno vplivajo na proces prestrezanja padavin in na zmanjšanje njihove intezitete ter razpršitev kinetične energije. Ti procesi pomembno vplivajo na vlago tal in infiltracijo v tla pod drevesi. Hitrost infiltracije v tla je bila največja na odprtem območju (5,97 cm/uro), sledila je infiltracija pod borom (5,55 cm/uro), najmanjša pa je bila pod brezo (3,76 cm/uro). Spremembe vlage v tleh pod brezo so bile hitrejše in bolj izrazite, še posebej pa na globini 16 cm, kar je bilo, kar je bilo posledica večje količine FR, SP in večje intenzitete prepuščenih padavin. Nasprotno pa so manjša količina in intenzitete prepuščenih padavin ter bolj postopno dovajanje CD pod borom povzročili počasnejše naraščanje vlage v tleh. To potrjujejo tudi statistično pomembne korelacije med komponentami prepuščenih padavin in vlago v tleh, ki kažejo, da se vlaga v tleh pod brezo hitreje in neposredno odziva na delež SP in FR, medtem ko se pod borom zaradi postopnega dovajanja CD vlaga odziva pozneje in počasneje. Poleg tega sezonske spremembe LAI bolj vplivajo na dinamiko vlage v tleh pod brezo kot pod borom. Uporaba modula SWMM za krošnje je natančno in eksplicitno simulirala hidrološke procese v krošnjah obeh dreves. To je izboljšalo prikaz prestrezanja padavin v modelu SWMM. Rezultati so pokazali, da je postopek prestrezanja v modulu učinkovito zajel časovno dinamiko prepuščenih padavin in odtoka po deblu (Tf + Sf) pod brezo in borom v različnih fenofazah. Med simuliranimi in opazovanimi vrednostmi Tf + Sf (r = 0,97-0,99) ter vrednostmi prestreženih padavin (r = 0,72) so bile ugotovljene močne korelacije pri vseh padavinskih dogodkih. Ugotovitve nadalje kažejo, da breza in bor na območju raziskave zmanjšata količino površinskega odtoka za 20–25 % in največji pretok za 16–25 % v različnih scenarijih in fenofazah. Scenarij sajenja mešanih vrst dreves (Scen3 s 50 % breze in 50 % bora) na splošno dosega večje koristi pri zmanjšanju površinskega odtoka in največjega pretoka v primerjavi s scenariji z eno vrsto dreves (Scen1 samo z brezo in Scen2 samo z borom). Analiza vodne bilance modela dodatno poudarja relativni prispevek prestrezanja krošenj (do 21,1 %) k zmanjšanju padavinskih voda pri brezi in boru, zlasti v obdobju vegetacije, pri majhnih do zmernih nevihtnih dogodkih in kadar so drevesa posajena nad neposredno povezanimi nepropustnimi površinami. Poleg tega infiltracija in shranjevanje vode v tleh pod krošnjami dreves predstavljata več kot 20 % vodne bilance, zlasti v obdobju mirovanja in odvisno od lastnosti tal. Na splošno ugotovitve te disertacije poudarjajo, da je sposobnost mestnih dreves za upravljanje padavinskih voda odvisna od procesov v krošenjah in pod njimi. Da bi zagotovili, da so hidrološke koristi mestnih dreves ustrezno upoštevane, je treba v analizo in modeliranje celovito vključiti hidrološke procese v krošnjah (tj. prestrezanje padavin, evapotranspiracija) in tleh.

• Keywords: doktorske disertacije, grajeno okolje, breza, bor, prestrežene padavine, površinski odtok, porazdelitev prepuščenih padavin, naravne rešitve, vlažnost tal, infiltracija, modul krošenj SWMM, mestna drevesa