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<p>Compound drought-heatwave (CDHW) events have greater impacts compared to singular events. Spanning nearly 40°of longitude and characterized by a complex climate, Northwest China is a globally recognized ecologically fragile region that is particularly sensitive to global climate change. This study investigates the spatiotemporal variation discrepancy of CDHW events in the eastern part of Northwest China (ENC) and the western part of Northwest China (WNC) utilizing daily maximum temperature and the standardized precipitation evapotranspiration index (SPEI). It further quantifies the internal driving forces and analyzed the relationship between CDHW events and sea surface temperature (SST) anomalies. Results indicate that the frequency, individual duration, and total duration of CDHW events exhibit significant asymmetry between ENC and WNC. In ENC, these factors show a notable increasing trend with an abrupt change occurring around 1997, whereas in WNC, they demonstrate decreasing trends without any abrupt changes. Moreover, changes in frequency contribute more significantly to total duration variations than do changes in individual duration. Across most areas of Northwest China, total heatwave duration and total drought duration exhibit inverse trends; however, there is a significant positive interdependence between them. In ENC, the rapid increase in total heatwave duration is the primary driver of the rise in total duration of CDHW events, contributing over 50% to the total duration of CDHW events. Conversely, in WNC, the reduction in total drought duration has been a major contributor to the decrease in total duration of CDHW events, accounting for over 40% in most cases. The coupling effect of total heatwave duration and total drought duration contributes less than 40% to the total duration of CDHW events in both ENC and WNC. Further analysis reveals a significant relationship between the monopolar mode and Indian Ocean SST (such as the Indian Ocean Warm Pool Area Index (IOWP-AI) and the Indian Ocean Basin-Wide Mode Index (IOBW), as well as the Tropical Indian Ocean Dipole Index (TIOD) and the Subtropical South Indian Ocean Dipole Index (SIOD)) from January to April. Specifically, an increase in Indian Ocean SST can trigger an anomalous anticyclone over the northwestern region, thereby favoring the occurrence of CDHW events. The rise in Pacific SST from January through May, along with the transition of Atlantic Multidecadal Oscillation (AMO) from negative to positive phases from January to August, strengthens the Mongolian anticyclonic anomaly, which in turn affects the north-south dipole mode of CDHW events. The well-documented asymmetry phenomenon in precipitation between ENC and WNC also manifests in CDHW (east-west dipole mode). However, this study does not identify any region with a consistently high correlation to this mode, warranting further investigation.</p>

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Variation characteristics in compound drought-heatwave events in Northwest China and the relationship with sea surface temperature

  • 期刊论文

  • 发表日期：

    2025年12月18日

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  • Suyan Wang,
  • Xin Li,
  • Fan Wang,
  • Dai Wang,
  • Ying Huang,
  • Haoyang Xu

摘要

Compound drought-heatwave (CDHW) events have greater impacts compared to singular events. Spanning nearly 40°of longitude and characterized by a complex climate, Northwest China is a globally recognized ecologically fragile region that is particularly sensitive to global climate change. This study investigates the spatiotemporal variation discrepancy of CDHW events in the eastern part of Northwest China (ENC) and the western part of Northwest China (WNC) utilizing daily maximum temperature and the standardized precipitation evapotranspiration index (SPEI). It further quantifies the internal driving forces and analyzed the relationship between CDHW events and sea surface temperature (SST) anomalies. Results indicate that the frequency, individual duration, and total duration of CDHW events exhibit significant asymmetry between ENC and WNC. In ENC, these factors show a notable increasing trend with an abrupt change occurring around 1997, whereas in WNC, they demonstrate decreasing trends without any abrupt changes. Moreover, changes in frequency contribute more significantly to total duration variations than do changes in individual duration. Across most areas of Northwest China, total heatwave duration and total drought duration exhibit inverse trends; however, there is a significant positive interdependence between them. In ENC, the rapid increase in total heatwave duration is the primary driver of the rise in total duration of CDHW events, contributing over 50% to the total duration of CDHW events. Conversely, in WNC, the reduction in total drought duration has been a major contributor to the decrease in total duration of CDHW events, accounting for over 40% in most cases. The coupling effect of total heatwave duration and total drought duration contributes less than 40% to the total duration of CDHW events in both ENC and WNC. Further analysis reveals a significant relationship between the monopolar mode and Indian Ocean SST (such as the Indian Ocean Warm Pool Area Index (IOWP-AI) and the Indian Ocean Basin-Wide Mode Index (IOBW), as well as the Tropical Indian Ocean Dipole Index (TIOD) and the Subtropical South Indian Ocean Dipole Index (SIOD)) from January to April. Specifically, an increase in Indian Ocean SST can trigger an anomalous anticyclone over the northwestern region, thereby favoring the occurrence of CDHW events. The rise in Pacific SST from January through May, along with the transition of Atlantic Multidecadal Oscillation (AMO) from negative to positive phases from January to August, strengthens the Mongolian anticyclonic anomaly, which in turn affects the north-south dipole mode of CDHW events. The well-documented asymmetry phenomenon in precipitation between ENC and WNC also manifests in CDHW (east-west dipole mode). However, this study does not identify any region with a consistently high correlation to this mode, warranting further investigation.