Abstract
Understanding the effects of land use change on evapotranspiration (ET) and its partitioning to transpiration and evaporation is important for accurately evaluating the likely environmental impacts on watershed water supply, climate moderation, and other ecosystem services (e.g., carbon sequestration and biodiversity). This study used a distributed hydrologic model, MIKE SHE, to partition evapotranspiration into soil evaporation, transpiration, ponded water evaporation, and interception, and examined how the ET partitions affected the water balance in the Qinhuai River Basin from 2000 to 2013. Simulated daily ET was compared to measurements at an eddy flux research site during 2016–2017 (R2 = 0.72). Degradation in rice-wheat rotation fields and expansion of impervious surfaces impacted not only total watershed evapotranspiration, which showed a significant downward trend (p < 0.05), but also its partitioning. A significant (p < 0.01) decrease in transpiration was detected. Ponded water evaporation was the only ET partition that exhibited a significant positive trend (p < 0.05). We concluded that the reduced transpiration as a result of land use and land cover change was the primary factor driving the variation of watershed scale evapotranspiration. In addition, there was an increase in annual water yield (23%) as a response to significant reduction in ET (7%) due to a 175% expansion of urban area in the study watershed. Our study provided insights to the mechanisms of land surface–water cycle interaction and better understanding of the effects of land use change on urban micro-climate such as “urban dry island” and “urban heat island” effects.
Highlights
Urbanization-associated land use and land cover (LULC) change is a global phenomenon that has negative impacts on local environment, society, and culture [1,2]
Vegetation transpiration has long been acknowledged to be a biological process that is closely related with ecosystem productivity, whereas evaporation (Ei, Es, and Ep ) is physically controlled processes representing evaporation from wet canopy or ground surfaces [12,19,20]
T represents the largest loss of water from vegetation and the transpiration fraction (T/ET), as an indicator of ET partition, is a key to interpreting vegetation–climate feedback [21,22], validating hydrological prediction, and improving agricultural water management practices [19]
Summary
Urbanization-associated land use and land cover (LULC) change is a global phenomenon that has negative impacts on local environment, society, and culture [1,2]. It is essential to understand these fundamental processes to accurately evaluate the likely environmental impacts of urbanization on watershed water supply, climate moderation, and other ecosystem services such as carbon sequestration [8,9]. Water 2020, 12, 645 energy, water, and carbon cycles and is recognized as a key variable to understanding the effects of urbanization on land surface processes [10,11,12]. Along with the expansion in urban land use that is well known to increase storm flow as a result of increase in impervious surface and decreased ET [2], T reduction during urbanization is likely to cause large impacts on regional ecosystem productivity and water yield, because the T process directly links plant growth and the carbon cycle [17,23]. In agricultural land, calculation of ET partitions is of great importance for water resource management practices, irrigation systems and irrigation regimes planning, and crop yield estimation [16]
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