Effect of Elevation on Variation in Reference Evapotranspiration under Climate Change in Northwest China

• Main Authors: Wei Liu, Linshan Yang, Meng Zhu, Jan F. Adamowski, Rahim Barzegar, Xiaohu Wen, Zhenliang Yin
• Format: Article
• Language: English
• Published: MDPI AG 2021-09-01
• Series: Sustainability
• Subjects: climate change; reference evapotranspiration; attribution analysis; elevation effect; Northwest China
• Online Access: https://www.mdpi.com/2071-1050/13/18/10151
• ISSN: 2071-1050

Through its effects on water and energy cycles, elevation plays an important role in modulating the spatial distribution of climatic changes in mountainous regions. A key hydrological indicator, reference evapotranspiration (ET₀) reflects the maximum amount of water transferred to the atmosphere from the land surface. The current scarcity of information regarding elevation’s impact on variation in ET₀ under climate change limits our understanding of the extent to which elevation modulates interactions between ET₀ and climate change and of the attendant processes involved. Drawing upon long-term (1960–2017) meteorological observations from 84 stations in Northwest China (NWC), we examined (i) spatial and temporal variations in ET₀; (ii) the sensitivity and contribution of air temperature (T), sunshine duration (SD), relative humidity (RH), and wind speed (WS) to ET₀; (iii) the existence of a relationship between elevation and ET₀ trends; and (iv) the major factor in controlling this relationship by using attribution analysis. Overall, annual ET₀ in NWC showed a declining trend between 1960 and 2017, though at a change point in 1993, the trend shifted from a decline to a rise. A significant correlation between temporal change in ET₀ and elevation confirmed the existence of a relationship between elevation and ET₀ variation. The effect of elevation on changes in ET₀ depended mainly on the elevation-based tradeoff between the contributions of T and WS: WS was the primary factor contributing to the decrease in ET₀ below 2000 m, and T was the dominant factor contributing to the increase of ET₀ above 2000 m. The rate of reduction in WS declined as elevation increased, thereby diminishing its contribution to variation in ET₀. The present study’s results can serve to guide agricultural irrigation in different elevation zones under NWC’s evolving climatic conditions.