Abstract
There have been few studies conducted on the changes in actual ET over the Loess Plateau, due to the lack of reliable ET data. Based on ET data simulated by the Community Land Model, the present study analyzed the changes in ET over the Loess Plateau. The results showed the domain-average ET to have decreased in the past 31 years, at a rate of 0.78 mm year−1. ET fluctuated much more strongly in the 1990s than in the 1980s and 2000s, and, apart from in autumn, ET decreased in all seasons. In particular, ET in summer comprised about half of the annual ET trend and had the sharpest trend, dominating the interannual decline. ET also decreased more sharply in the semiarid than semihumid regions. The declining trend of ET was attributed to declining precipitation and air humidity. Locally, the ET trend was closely related to local mean annual precipitation: in areas with precipitation less than 400 mm, ET showed a decreasing trend; in areas with precipitation larger than 600 mm, ET showed an increasing trend; and in areas with precipitation in the range of 400–600 mm could be classified as a transitional zone.
Highlights
Evapotranspiration (ET)—the process of transferring water from the land surface to the atmosphere—is the link between the global water cycle, energy cycle, and carbon cycle and is of critical importance for agriculture, hydrology, ecology, and the climate system [1, 2]
Potential ET is decreasing in most regions of China; pan evaporation and potential ET are increasing in the Loess Plateau [24, 25]
The decreasing trend implies that ET decreased more sharply than precipitation during the study period; water recycling from the land surface to the atmosphere was becoming weaker, as was the regional water cycle
Summary
Evapotranspiration (ET)—the process of transferring water from the land surface to the atmosphere—is the link between the global water cycle, energy cycle, and carbon cycle and is of critical importance for agriculture, hydrology, ecology, and the climate system [1, 2]. Many studies have investigated trends of pan evaporation, potential ET, and reference ET regionally or globally. These trends, are not consistent among different regions of the globe. Global warming would increase pan evaporation, but there are only a few regions where the evidence supports this inference, including Israel [5], northeast Brazil [6], Australia [7], and China [8]. Potential ET is decreasing in most regions of China; pan evaporation and potential ET are increasing in the Loess Plateau [24, 25]. We first validated the ET products of GLDAS using ET data observed by an eddy covariance (EC) system at four land surface observatories in the Loess Plateau. The relationship between ET trends and mean annual precipitation locally was analyzed
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