Altitudinal Differences in Decreasing Heat Deficit at the End of the Growing Season of Alpine Grassland on the Qinghai–Tibetan Plateau from 1982 to 2022

Yusi Zhang, Gang Bao (), Yuhai Bao, Zhihui Yuan, Wendu Rina and Siqin Tong
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Yusi Zhang: College of Geographical Science, Inner Mongolia Normal University, Hohhot 010022, China
Gang Bao: College of Geographical Science, Inner Mongolia Normal University, Hohhot 010022, China
Yuhai Bao: College of Geographical Science, Inner Mongolia Normal University, Hohhot 010022, China
Zhihui Yuan: College of Water Conservancy and Civil Engineering, Inner Mongolia Agricultural University, Hohhot 010022, China
Wendu Rina: Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100049, China
Siqin Tong: College of Geographical Science, Inner Mongolia Normal University, Hohhot 010022, China

Land, 2025, vol. 14, issue 4, 1-20

Abstract: As a measure of the accumulated heat deficit during the growing season transition, cooling degree days (CDDs) play a crucial role in regulating vegetation phenology and ecosystem dynamics. However, systematic analyses of CDD trends and their driving mechanisms remain limited, particularly in high-altitude regions where climate variability is pronounced. This study investigated the spatiotemporal variability in CDDs from 1982 to 2022 in alpine grasslands on the Qinghai–Tibetan Plateau (TP) and quantified the contributions of key climatic factors. The results indicate that lower CDD values (<350 °C-days) were predominantly found in warm, arid regions, whereas higher CDD values (>600 °C-days) were concentrated in colder, wetter areas. Temporally, area-averaged CDDs exhibited a significant decline, decreasing from 490.9 °C-days in 1982 to 495.8 °C-days in 2022 at a rate of 3.8 °C-days per year. Elevation plays a critical role in shaping CDD patterns, displaying a nonlinear relationship: CDDs decrease as elevation increases up to 4300 m, beyond which they increase, suggesting a transition from global climate-driven warming at lower elevations to local environmental controls at higher elevations, where snow–albedo feedback, topographic effects, and atmospheric circulation patterns regulate temperature dynamics. Tmax was identified as the dominant climatic driver of CDD variation, particularly above 4300 m, while radiation showed a consistent positive influence across elevations. In contrast, precipitation had a limited and spatially inconsistent effect. These findings emphasize the complex interactions between elevation, temperature, radiation, and precipitation in regulating CDD trends. By providing a long-term perspective on CDD variations and their climatic drivers, this study enhances our understanding of vegetation–climate interactions in alpine ecosystems. The results offer a scientific basis for modeling late-season phenological changes, ecosystem resilience, and land-use planning under ongoing climate change.

Keywords: Qinghai–Tibetan Plateau; alpine grassland; climate change; cooling degree days (CDDs) (search for similar items in EconPapers)
JEL-codes: Q15 Q2 Q24 Q28 Q5 R14 R52 (search for similar items in EconPapers)
Date: 2025
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