The Effects of Urbanization on Watershed Evapotranspiration and Surface Energy Budget in Southern China

Abstract:

Observed and modeled meteorological, ecohydrological, and ecological changes in urbanizing regions have linked to the changes in land surface actual evapotranspiration (ET). The present modeling study focused on a large fast urbanizing rice paddy-dominated region, the Qinhuai River Basin (QRB) in southern China. The remote sensing-based data driven Surface Energy Balance Algorithm for Land (SEBAL) model was parameterized to simulate the instantaneous spatial variations of surface heat fluxes for the time period from 2002 – 2016 when the study basin experienced dramatic changes in both climate and land use. Modeled energy fluxes were scaled-up to estimate continuous ET (ET_a) for the rice-growing season during a 15-year study period. The model performances were evaluated using eddy covariance measurements at a rice paddy site and a global remote-sensing MOD16 ET product for the entire basin. We found that SEBAL performed well overall with a mean relative error of 3.5%, 5.7% and 14% for net radiation (R_n), latent heat (LE), and ET_a, respectively. During 2002 – 2016, simulated Rn, LE, and ET_a decreased significantly over the Urban-Rural Interface (URI) area. Our study suggests that the URI area is the ‘hot spots’ of ecohydrological change within a heterogeneous basin. The rapid change in energy and water balance in the URI area is likely to bring a series chain reactions in environmental changes such as increase in storm runoff, non-point source water pollution, and Urban Heat Island (UHI) and Urban Dry Island (UDI) as identified in our previous studies in this basin. New process-based understanding reported in this study is essential for properly parameterizing regional climate and ecohydrological model to assess urbanization effects on regional and climate and water resource.