The current approaches have known limitations to understanding the coupling of terrestrial ecosystem evapotranspiration (ET) and photosynthesis (referred to as gross primary productivity, GPP). To better characterize the relationship between ET and GPP, we developed a novel remote sensing (RS)-driven approach (RCEEP) based on the underlying water use efficiency (uWUE). RCEEP partitions transpiration (T) from ET using a RS vegetation index (VI)-derived ratio of T to ET (VI-fT) and then links T and GPP via RS VI-derived Gc (VI-Gc) rather than leaf-to-air vapor pressure difference. RCEEP and other two uWUE versions (VI-T or VI-G), which only incorporate VI-fT or VI-Gc , were evaluated and compared with the original uWUE model in terms of their performances (Nash-Sutcliffe efficiency, NSE) in estimating GPP from ET over 180 flux sites covering 11 biome types over the globe. Results revealed better performances of VI-T and VI-G compared to the original uWUE, implying remarkable contributions of VI-fT and VI-Gc to a more meaningful relationship between ET and GPP. RCEEP yielded the best performances with a reasonable mean NSE value of 0.70 (0.76) on a daily (monthly) scale and across all biome types. Further comparisons of RCEEP and approaches modified from recent studies revealed consistently better performances of RCEEP and thus, positive implications of introducing VI-fT and VI-Gc in bridging ecosystem ET and GPP. These results are promising in view of improving or developing algorithms on coupled estimates of ecosystem ET and GPP and understanding the GPP dynamics concerning ET on a global scale.

Recent studies suggest Asian Water Tower (AWT) is vulnerable to climate change with a detrimental effect on water and food security. Comprehensive information about the spatio-temporal variability of lakes, an important freshwater resource, is lacking. Therefore, we analyzed 89,480 Landsat images to examine the change in the lakes size around AWT between 1977±2 and 2020±2. Sequentially, the trends of precipitation, snow water equivalent, glacier mass, and permafrost were analyzed to understand what caused the lake’s alteration. According to our findings, from 1977±2 to 2020±2, 84% of mapped lakes grew during the wet season, whereas 81% of the lakes grew during the dry season. Lakes in the Inner TP and Tarim Interior basins expanded dramatically. The Helmand, Amu Darya, and Yangtze basins are the primary locations of shrinking lakes. The Aral Sea shrunk by 90%. From the region as a whole, the alpine lakes showed a shrinking trend and the plain lakes showed an expanding trend from 1977±2 to 1990±2, and vice versa from 1990±2 to 2020±2. Glacial loss and permafrost thawing were corresponding to lake expansion in the Inner TP, Tarim Interior, Syr Darya, and Mekong basins. Permafrost discontinuities may cause Indus and Ganges to not grow significantly in lakes with increased recharge to the basin. Extreme droughts depleted the lake in Helmand. Human intervention have caused the shrinking of the Aral Sea and the lakes in the lower Yangtze River. As AWT retreats and feeds lakes, we need to take immediate action for managing risks and adaption.