Improved understanding of factors affecting urban hydrological cycle

Tutkimustuotos: OpinnäyteVäitöskirjaArtikkelikokoelma


The processes related to urban development (urbanisation, densification, irrigation and worsened air quality) are assumed to affect the urban hydrological cycle, but little is known about the impact of the individual processes. One of the reasons for the knowledge gaps is the lack of measurements for the needed resolution or for the period of interest. Reanalysis products can provide the needed data, but those have not been evaluated in urban areas. Furthermore, model evaluation is commonly made against eddy covariance (EC) measurements, but little is known of the uncertainties related to often non-ideal instrument location at urban areas. To answer the uncertainties in urban hydrological cycle, Surface Urban Energy and Water Balance Scheme (SUEWS) forced with the WATCH Forcing Data is used. The analyses are performed in cities located in different climate conditions (Vancouver, London and Beijing) and above varying urban land covers (dense city centre and suburban areas). To understand better the uncertainties related to model evaluation, uncertainties of EC method are analysed using two identical EC systems at the same level close to each other in central Helsinki. The most crucial reanalysis variables to correct are precipitation due to coarse spatial resolution and the incoming solar radiation due to haze. SUEWS performs well when forced with corrected WATCH data, which allows detailed analysis of urban hydrological cycle. The irrigation has the dominant effect over densification and urbanisation on suburban hydrological cycle. The densification increases the runoff as much as the initial urbanisation, even though the increase of impervious surfaces is much smaller. The haze decreases evaporation which increases runoff and soil infiltration especially at smaller daily precipitation totals. This is expected to flush pollutants from surfaces and increase the pollutant loads of urban waters. After the post-processing of the EC data, systematic uncertainties in latent heat flux originating from a single-point observation above dense city centre due to removal of large fraction of wind disturbed data are only 8%. Thus, useful and representative EC observations can be obtained from urban areas, despite the errors induced by the non-ideal location. The results of this thesis answer the uncertainties in urban hydrological cycle by bringing new knowledge of the dominant factors in the urban water balance and the representativeness of reanalysis data in urban areas. The results can help urban planners to design sustainable cities being able to mitigate and adapt to the common problems in urban hydrology.
Myöntävä instituutio
  • Matemaattis-luonnontieteellinen tiedekunta
  • Järvi, Leena , Valvoja
  • Leppäranta, Matti, Valvoja
Opinnäytetyön sponsorit
Myöntöpäivämäärä10 huhtik. 2019
Painoksen ISBN978-951-51-4979-4
Sähköinen ISBN978-951-51-4980-0
TilaJulkaistu - 22 maalisk. 2019
OKM-julkaisutyyppiG5 Tohtorinväitöskirja (artikkeli)


  • 114 Fysiikka
  • Urban hydrology
  • urbanization
  • Water balance
  • Energy balance

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