Abstract
Climate variation and underlying surface dynamics have caused a significant change in the trend of evapotranspiration (ET) in the Yellow River Basin (YRB) over the last two decades. Combined with the measured rainfall, runoff and gravity recovery and climate experiment (GRACE) product, five global ET products were firstly merged using a linear weighting method. Linear slope, “two-step” multiple regression, partial differential, and residual methods were then employed to explore the quantitative impacts of precipitation (PCPN), temperature (Temp), sunshine duration (SD), vapor pressure deficit (VPD), wind speed (WS), leaf area index (LAI), and the residual factors (e.g., microtopography changes, irrigation, etc.) on the ET trend in the YRB. The results show that: (1) The ET estimates were improved by merging five global ET products using the linear weighting method. The sensitivities of climatic factors and LAI on the ET trend can be separately calculated using proposed “two-step” statistical regression method; (2) the overall ET trend in the entire study area during 2000–2018 was 3.82 mm/yr, and the highest ET trend was observed in the Toudaoguai-Longmen subregion. ET trend was dominantly driven by vegetation greening, with an impact of 2.47 mm/yr and a relative impact rate of 51.16%. The results indicated that the relative impact rate of the residual factors (e.g., microtopography, irrigation, etc.) on the ET trend is up to 28.17%. The PCPN and VPD had increasing roles on the ET trend, with impacts of 0.45 mm/yr and 0.05 mm/yr, respectively, whereas the Temp, SD, and WS had decreasing impacts of –0.19 mm/yr, –0.15 mm/yr, and –0.17 mm/yr, respectively. (3) The spatial pattern of impact of specific influencing factor on the ET trend was determined by the spatial pattern of change trend slope of this factor and sensitivity of ET to this factor. ET trends of the source area and the Qingtongxia–Toudaoguai were dominated by the climatic factors, while the residual factors dominated the ET trend in the Tangnaihai–Qingtongxia area. The vegetation restoration was the dominant factor causing the increase in the ET in the middle reaches of the YRB, and the impact rates of the LAI were ranked as follows: Yanhe Rive > Wudinghe River > Fenhe River > Jinghe River > Beiluohe River > Qinhe River > Kuyehe River > Yiluohe River.
Highlights
Evapotranspiration (ET) is a key process in the terrestrial water cycle and the surface energy balance [1]
The results show that the ensemble ET could more accurately capture the spatial-temporal dynamics of ET in the Yellow River Basin (YRB) from 2000 to 2018
Five global ET products were merged by a linear weighting method
Summary
Evapotranspiration (ET) is a key process in the terrestrial water cycle and the surface energy balance [1]. Climate models, and land surface models have been gradually integrated into the numerical simulation of the ET, scientists have developed numerous global and regional ET products. These products can be divided into three main categories based on the different estimation methods: (1) products interpolated using field measurements and machine learning methods (e.g., the marginal treatment effects method [7]); (2) products simulated using a remotely sensed evapotranspiration model (e.g., the moderate resolution imaging spectroradiometer [8] and probable maximum loss (PML) [9]); and (3) reanalysis data and products assimilated using different land surface models (e.g., the Japanese 55-year reanalysis [10], global land data assimilation system (GLDAS) [11], and global land evaporation Amsterdam model (GLEAM) [12]). There are large inconsistencies in the spatial and temporal distributions of the ET products due to the complex model structures, inaccurate physical parameters, and input datasets with different scales
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