Impacts of Summer Extreme Precipitation Events on the Hydrothermal Dynamics of the Active Layer in the Tanggula Permafrost Region on the Qinghai‐Tibetan Plateau

Abstract

The characteristics of long‐term variation for extreme precipitation events were analyzed at the Tanggula site in the continuous permafrost regions of the Qinghai‐Tibetan Plateau (QTP). In addition, the impacts of extreme precipitation events in summer on soil thermal‐moisture dynamics were also investigated. The results showed that local extreme precipitation indices fluctuated significantly and that the trend magnitudes of local very wet days (R95p), annual total wet‐day precipitation (PRCPTOT), number of heavy precipitation days (R10mm), maximum length of dry spell (CDD), and simple daily intensity index (SDII) were larger than those of the western QTP, other regions of China, and even the global average. The freeze‐thaw cycling in the local active layer occurred from October to the next September during 2006 to 2014. The influence of extreme precipitation event in summer on local soil hydrothermal conditions could reach soil depths up to 105 cm or so, and these were more pronounced than with light or moderate precipitation events. Soil temperature reacted more promptly to local extreme precipitation events than did soil moisture. The rate at which local soil temperature fell after an extreme precipitation event was greater than the rate of increasing temperature on nonprecipitation days. Moreover, the amount of precipitation received during extreme precipitation events had a greater effect on local soil moisture and temperature than duration time for these events. Consecutive extreme precipitation events with a longer duration time did not necessarily to have a greater effect than a single precipitation event with a shorter duration. Finally, the thawing process of active layer and local water migration modes could also affect the response of soil hydrothermal conditions to an extreme precipitation event to a large extent.

Permafrost warming near the northern limit of permafrost on the Qinghai–Tibetan Plateau during the period from 2005 to 2017: A case study in the Xidatan area

“…Theoretically, rainfall can increase soil moisture and enhance thermal conductivity of the soil 23 especially for a field such as site A where the soil is far from saturated. Although recent studies have suggested that there remains uncertainty about the impact of precipitation on the thermal regime of the active layer, 24,25 it is possible that abundant precipitation strengthened the thawing of the active layer in summer based on our observations.…”

Thermal Regime and Variations in the Island Permafrost Near the Northern Permafrost Boundary in Xidatan, Qinghai–Tibet Plateau

“…The annual mean air temperature and accumulated precipitation recorded at a national weather station (Wudaoliang station) near the Xidatan region is shown in Figure 8A, with results indicating that both the air temperature and the amount of precipitation in the area have noticeably increased over the past 40 years. Recent studies have demonstrated that the occurrence of a wet climate on the QTP can reduce the thermal responses of permafrost to warming, thereby preventing the degradation of permafrost, especially in arid and semiarid zones (Zhang et al, 2021), however, the extreme precipitation events in summer can have a thermal impact on permafrost (Zhu et al, 2017). Meanwhile, persistent climate warming is also the reason for the enhanced permafrost degradation in this region.…”

Long‐distance atmospheric moisture dominates water budget in permafrost regions of the Central Qinghai‐Tibet plateau

“…As a result, soil moisture during this period is higher than in the other months that have abundant precipitation. This is especially true for the extreme precipitation events (Zhu et al, 2017). It is also worth noting that precipitation is a predominant source for soil moisture (Zhu, Wu, et al, 2019).…”