Effects of 1.5°C and 2°C of warming on regional reference evapotranspiration and drying: A case study of the Yellow River Basin, China

Abstract

Reference evapotranspiration (ETo) is one of the most important factors influencing hydrologic and climatic quantities, and increases in ETo are often considered as a primary cause for drying under global warming scenarios. Based on bias‐corrected data from the Half a degree Additional Warming, Prognosis and Projected Impacts (HAPPI) experiment, we investigated changes in ETo and drying across the Yellow River Basin (YRB) for 1.5°C and 2°C stabilized warming, relative to the current decade (2006–2015). We used changes in the climatic water deficit (WD: defined as precipitation (P) minus (ETo) to determine drying and wetting trends. Results projected that mean annual ETo would increase significantly over the whole YRB, under 1.5°C and 2°C warming scenarios, with an increase of 4.54% (1.57–7.59% full uncertainty range) and 7.66% (4.49–10.61%), at 1.5°C and 2°C, respectively, averaged over the YRB for the multi‐model mean. It is unclear whether the YRB source region (the NE region of the Tibet Plateau) would be drier or wetter under 1.5°C and 2°C of warming, although it is likely that the N regions of the YRB, and the whole YRB except for the source region will be drier under 1.5°C and 2°C warming scenarios, respectively. With an additional 0.5°C warming, further intensification of drying is projected in the whole YRB, resulting from a more pronounced increase in ETo, and lesser increase/decrease in P. The increased ETo projected under a 0.5°C additional warming was mainly attributed to rising maximum temperatures (tasmax). These results highlight the importance of ETo, in terms of potential future YRB drying, and our study suggests that limiting future warming to 1.5°C would impact regional drying the least.

Variation in Reference Evapotranspiration over the Tibetan Plateau during 1961–2017: Spatiotemporal Variations, Future Trends and Links to Other Climatic Factors

“…Our research found that the change in the ET 0 between 1961 and 2017 had the greatest positive correlation with Tmean, followed by U 2 and SD. Jian et al similarly found an increase in the ET 0 , due to temperature changes [74]. Chen et al and Xie and Zhu concurred that wind speed has an important influence on the ET 0 of the TP [75,76].…”

Expansion of drylands in China with an additional half a degree warming

“…The regional warming in China, especially over drylands (Huang et al ., 2017), has a rate that is much faster than the global mean air temperature (see Figure S2; Sun et al, 2019). In addition, the significant increase of maximum air temperature is suggested to make the largest contribution to the increase of PET, for example, over the Yellow River basin (Jian et al ., 2020). Therefore, the high SNR of PET change in China may be attributed to the high SNR of air temperature change.…”

“…Observed and projected PET based on Equation () were obtained from Jian et al . (2020), in which detailed calculation process was introduced.…”

“…The t test (Wilks, 2005) was used to test the difference of mean among different experiments. It has been found that there exist some discrepancies among AGCMs and thus the individual ensemble members for each AGCM rather than only the ensemble mean were analysed in this study (e.g., Chevuturi et al ., 2018; Zhai et al ., 2018; Jian et al ., 2020).…”

“…Two questions then arise in the scientific community: (a) What type of world would be achieved if keeping the world at either +1.5°C or +2.0°C above preindustrial temperature level; (b) What can we benefit from the half a degree less warming? To address these questions, a lot of efforts have been devoted to compare the climatic impacts of the two warming levels on both global and regional scales (e.g., Sanderson et al ., 2017; Schleussner et al ., 2017; Chevuturi et al ., 2018; Park et al ., 2018; Su et al ., 2018; Zhang et al ., 2018; Wei et al ., 2019; Jian et al ., 2020). Currently, many studies suggested that there exist substantial differences in the impacts of climate changes between the warming levels of 1.5 and 2.0°C, and the additional 0.5°C warming does matter, although it sounds small (Schleussner et al ., 2016; 2017; Huang et al ., 2017; King and Karoly, 2017; IPCC, 2018; Jackson et al ., 2018; Leng, 2018; Lin et al ., 2018; Park et al ., 2018; Su et al ., 2018; Zhang et al ., 2018).…”