Abstract
Spatiotemporal patterns of evapotranspiration (ET) and its controlling factors are important for ecosystem services and water resources management in the Chinese Loess Plateau (CLP). In this study, we assessed the spatial patterns of ET and then investigated the interannual variability of ET and its relationships with climate variability and vegetation coverage changes at the timescales of annual, active growing season, as well as different seasons across the entire CLP from 2000 to 2014. A MODIS-derived ET dataset, ground-based datasets of precipitation and atmospheric evaporative demand (AED), and a remote-sensing dataset of Normalized Difference Vegetation Index (NDVI) were comprehensively analyzed. Results showed that mean annual ET varied distinctly among different vegetation zones, generally higher in the more humid southeastern parts of the CLP. Summer ET and ET over active growing season significantly increased for more than 40% of the entire CLP area, and winter ET significantly decreased over ~70% of the entire CLP region, while annual ET, spring ET, and autumn ET remained quite stable during 2000–2014. Per-pixel interannual variability of ET was mainly positively correlated with that of precipitation and NDVI except for winter, but negatively correlated with AED trends. Our study also demonstrated that ET variation trends were exactly consistent for the entire CLP region, the areas mainly implemented with the Grain for Green (GFG) project, and other CLP areas not implemented with the GFG project during 2000–2014. Our findings suggest that the spatiotemporal patterns of CLP ET were mainly water-limited, and climate variability played an essential role in shaping the interannual variability of ET in the CLP. This study will improve our understanding on the ET variations over water-limited areas under climate and vegetation coverage changes.
Highlights
Ecosystem evapotranspiration (ET) is a key process and component in the terrestrial water cycle and energy balance [1,2], which is composed of vegetation transpiration, soil evaporation, and evaporation of canopy interception [2,3]
It is necessary to quantify the effects of climate changes and vegetation coverage changes on ET variations using modelling techniques in the future, if a deeper understanding of the temporal variations in the Chinese Loess Plateau (CLP) ET and its underlying mechanisms is to be achieved
Spatiotemporal variations in ecosystem ET and its relationships with regional climate variability and vegetation coverage changes were investigated at the timescales of annual, active growing season, and different seasons across the entire CLP from 2000 to 2014, mainly based on a MODerate Resolution Imaging Spectroradiometer (MODIS) ET dataset
Summary
Ecosystem evapotranspiration (ET) is a key process and component in the terrestrial water cycle and energy balance [1,2], which is composed of vegetation transpiration, soil evaporation, and evaporation of canopy interception [2,3]. ET and its controlling factors is crucial for water resources management especially for the water-limited regions around the world [1,7,8]. Several revegetation or ecological restoration projects have been enforced in this region ever since the 1950s aiming at relieving the environmental pressure in the CLP, which have remarkably altered the land surface characteristics (e.g., increasing vegetation coverage) and ecosystem water cycles (e.g., declining runoff and soil moisture), because of the implementation of the Grain for Green (GFG) project in 1999 [11,12,13,14,15]. As a key process within the water cycle, it is essential to comprehensively assess the spatiotemporal patterns of ecosystem ET for the water resources management across the CLP region
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