Numerical modeling of the responses of soil temperature and soil moisture to climate change over the Tibetan Plateau, 1961–2010

Abstract

Changes in soil temperature (ST) and soil moisture (SM) are essential for climate change and ecosystem assessments. Previous investigations on the ST and SM on the Tibetan Plateau (TP) are mainly based on the situ observation and the satellite products. In this study, the improved Community Land Model version 4.5 (CLM4.5), with proper parameter optimization and surface datasets update, is used to estimate the response of ST and SM in the TP to climate change in the long‐term time series from 1961 to 2010. After validating the reasonability of the simulated results using the observations, the spatial distribution of changes in ST and SM in annual and seasonal time series since 1960s, 1980s, 1990s, are investigated respectively and the changes of precipitation (Pr) and surface evaporation (Ev) are also analysed to understand the cause of changes objectively. As a whole, the soil was warming and wetting at the maximum value of 0.31°C/decade and 0.77%/decade since the 1960s. However, the warming process in soil mainly occurred in the 1980s while the wetting tendency is detected since the 1990s extensively. Except for the influence of air warming, the enhanced Pr and Ev might also be indispensable factors that caused the intensive wetting process but damped warming process in soil. Summer is the favourable season for the thermal and hydraulic variation since the 1980s. There exists the striking warmer and drier trend in the eastern TP since 1980s while the colder and wetter condition in the western TP since the 1990s. The magnitude of variation in soil is magnified from 1990s under the continuing impact of climate change.

Dynamics of Freezing/Thawing Indices and Frozen Ground from 1961 to 2010 on the Qinghai-Tibet Plateau

“…Figure 1d shows that the conversions from permafrost into SFG was prevailing across the entire QTP, especially in the southern QTP. The shortens of freezing and thawing duration in active layer in the 1990s is likely to cause permafrost more vulnerable to climate change, which coincides with previous results [39]. Our results indicated that, in contrast to 1990s, an area counting 33.33 % of permafrost on the QTP thawed into SFG in 2000s.…”

“…Moreover, the reliabilities of air temperature and precipitation components of the dataset have also been confirmed using the observational records on the QTP, prior the numerical simulation [39]. Additionally, the in-situ observations across the QTP also confirmed the simulation ability of the CLM4.5 to reproduce the soil temperature values in a long run [36,39], which were used to calculate the ground freezing/thawing indices (GFI/GTI) in this study. Meanwhile, the air freezing/thawing indices (AFI/ATI) presented in this study were also calculated using the near-surface (2 m above the ground) atmospheric temperatures derived from this data set.…”

“…Before it was released by the Beijing Normal University (China, hereafter BNU), the reasonability of the dataset has been validated through comparisons of the corresponding components with the National Centers for Environmental Prediction Climate Forecast System Reanalysis dataset and the Princeton meteorological forcing dataset [38]. Moreover, the reliabilities of air temperature and precipitation components of the dataset have also been confirmed using the observational records on the QTP, prior the numerical simulation [39]. Additionally, the in-situ observations across the QTP also confirmed the simulation ability of the CLM4.5 to reproduce the soil temperature values in a long run [36,39], which were used to calculate the ground freezing/thawing indices (GFI/GTI) in this study.…”

Sensitivity Analysis of the Noah‐MP Land Surface Model for Soil Hydrothermal Simulations Over the Tibetan Plateau

“…Therefore, we replaced this data set with a new soil property data set released by Beijing Normal University (hereafter referred to as the BNU data set, Shangguan et al, 2013). Fang et al (2021) compared these two datasets and demonstrated that the BNU data set can better describe the soil characteristics of the TP. We used the soil loam, clay, and sand contents from this data set and soil pedo-transfer functions (Saxton & Rawls, 2006) provided in the model to convert these content values to the soil parameters required for the model simulations.…”

Changes of timing and duration of the near-surface soil freeze/thaw cycles on the Tibetan Plateau in the highly wetting period from 1998 to 2005

“…To drive CLM4.5 from 1979 to 2010, atmospheric datasets of high resolution (temporal of 3 hourly and spatial of 1 km) were used in this study. Observations were collected from nearly 700 stations over China (Li et al, 2014), and their reliability and the model outputs, including soil temperature and soil moisture, have been validated seriously using in-situ observations across the TP (Fang et al, 2021). More detailed information about the atmospheric datasets can be found in the website (http://globalchange.bnu.edu.cn/research).…”