Seasonal contributions of vegetation types to suburban evapotranspiration

Abstract

[1] Evapotranspiration is an important term of energy and water budgets in urban areas and is responsible for multiple ecosystem services provided by urban vegetation. The spatial heterogeneity of urban surface types with different seasonal water use patterns (e.g., trees and turfgrass lawns) complicates efforts to predict and manage urban evapotranspiration rates, necessitating a surface type, or component-based, approach. In a suburban neighborhood of Minneapolis-Saint Paul, Minnesota, United States, we simultaneously measured ecosystem evapotranspiration and its main component fluxes using eddy covariance and heat dissipation sap flux techniques to assess the relative contribution of plant functional types (evergreen needleleaf tree, deciduous broadleaf tree, cool season turfgrass) to seasonal and spatial variations in evapotranspiration. Component-based evapotranspiration estimates agreed well with measured water vapor fluxes, although the imbalance between methods varied seasonally from a 20% overestimate in spring to an 11% underestimate in summer. Turfgrasses represented the largest contribution to annual evapotranspiration in recreational and residential land use types (87% and 64%, respectively), followed by trees (10% and 31%, respectively), with the relative contribution of plant functional types dependent on their fractional cover and daily water use. Recreational areas had higher annual evapotranspiration than residential areas (467 versus 324 mm yr −1 , respectively) and altered seasonal patterns of evapotranspiration due to greater turfgrass cover (74% versus 34%, respectively). Our results suggest that plant functional types capture much of the variability required to predict the seasonal patterns of evapotranspiration among cities, as well as differences in evapotranspiration that could result from changes in climate, land use, or vegetation composition.

Infrared and millimetre-wave scintillometry in the suburban environment – Part 2: Large-area sensible and latent heat fluxes

“…For comparison, summertime daily evapotranspiration rates from UK woodlands are around 4-5 mm day −1 (Roberts et al, 2005;Thomas et al, 2011). Evapotranspiration rates from residential and recreational areas in suburban MinneapolisSaint Paul, Minnesota are around 3 mm day −1 in summer (Peters et al, 2011), comparable to the BLS-MWS results shown here, but near zero in winter (conditions are much colder and drier). The Swindon results are thus comparable to other published findings, but to obtain concurrent Q H and Q E at this scale is rare.…”

Multi-season eddy covariance observations of energy, water and carbon fluxes over a suburban area in Swindon, UK

“…12). The proportion of evergreen trees around the measurement tower is small, so this is most likely due to grass growth in early spring, occurring before leaf-out of deciduous trees (Peters et al, 2011). Warmer temperatures in the urban environment can also encourage early onset of the growing season compared to rural areas (Zhang et al, 2004).…”

Hydrological and vegetation response to climate change in a forested mountainous catchment

“…At the same time, hot summers lead to boreal forest decline (Joos et al 2001;Lucht et al 2006). Moreover, deciduous forests and herbaceous biomes are characterized by a lower evapotranspiration compared to evergreen forests (Zhang et al 2001;Peters et al 2013).…”