Land–Climate Interaction Over the Tibetan Plateau

Abstract

The Tibetan Plateau (TP) is the largest and highest plateau on Earth. Due to its elevation, it receives much more downward shortwave radiation than other areas, which results in very strong diurnal and seasonal changes of the surface energy components and other meteorological variables, such as surface temperature and the convective atmospheric boundary layer. With such unique land process conditions on a distinct geomorphic unit, the TP has been identified as having the strongest land/atmosphere interactions in the mid-latitudes.Three major TP land/atmosphere interaction issues are presented in this article: (1) Scientists have long been aware of the role of the TP in atmospheric circulation. The view that the TP’s thermal and dynamic forcing drives the Asian monsoon has been prevalent in the literature for decades. In addition to the TP’s topographic effect, diagnostic and modeling studies have shown that the TP provides a huge, elevated heat source to the middle troposphere, and that the sensible heat pump plays a major role in the regional climate and in the formation of the Asian monsoon. Recent modeling studies, however, suggest that the south and west slopes of the Himalayas produce a strong monsoon by insulating warm and moist tropical air from the cold and dry extratropics, so the TP heat source cannot be considered as a factor for driving the Indian monsoon. The climate models’ shortcomings have been speculated to cause the discrepancies/controversies in the modeling results in this aspect. (2) The TP snow cover and Asian monsoon relationship is considered as another hot topic in TP land/atmosphere interaction studies and was proposed as early as 1884. Using ground measurements and remote sensing data available since the 1970s, a number of studies have confirmed the empirical relationship between TP snow cover and the Asian monsoon, albeit sometimes with different signs. Sensitivity studies using numerical modeling have also demonstrated the effects of snow on the monsoon but were normally tested with specified extreme snow cover conditions. There are also controversies regarding the possible mechanisms through which snow affects the monsoon. Currently, snow is no longer a factor in the statistic prediction model for the Indian monsoon prediction in the Indian Meteorological Department. These controversial issues indicate the necessity of having measurements that are more comprehensive over the TP to better understand the nature of the TP land/atmosphere interactions and evaluate the model-produced results. (3) The TP is one of the major areas in China greatly affected by land degradation due to both natural processes and anthropogenic activities. Preliminary modeling studies have been conducted to assess its possible impact on climate and regional hydrology. Assessments using global and regional models with more realistic TP land degradation data are imperative.Due to high elevation and harsh climate conditions, measurements over the TP used to be sparse. Fortunately, since the 1990s, state-of-the-art observational long-term station networks in the TP and neighboring regions have been established. Four large field experiments since 1996, among many observational activities, are presented in this article. These experiments should greatly help further research on TP land/atmosphere interactions.

Area, lake-level and volume variations of typical lakes on the Tibetan Plateau and their response to climate change, 1972–2019

“…Amidst the mountains spread a range of hills, lakes and gorges, constituting undulation alpine prairie. The central and eastern parts occupy about 50% of the Tibetan Plateau, with the surface covered by alpine prairie and meadows; its northern and western areas are covered by alpine and temperate deserts, while in the southeast Tibetan Plateau, alpine boreal, evergreen, and deciduous forests are dominant (Xue, Ma, and Li 2017). There are intensive rivers and lakes in the Tibetan Plateau.…”

Numerical study on the climatic effect of the lake clusters over Tibetan Plateau in summer

“…During boreal summer, TP serves as a huge, elevated heat source to the middle troposphere (Yanai et al 1992;Wu et al 2012;Xue et al 2017). The powerful sensible heat pump effect of the TP can drive the low-level moisture advection from Bay of Bengal to the Indian peninsula, generating the large rainfall center with the intensity approximately 10 mm day −1 over the Ganges Plain (Fig.…”

“…Overall, the lake effects are found to be prominent in lakeabundant regions but exhibit distinctive diurnal and seasonal features in different regions, depending on the lake intrinsic natures, surrounding topography and background atmospheric circulations (Argent et al 2015;Subin et al 2012;Wen et al 2015a). Compared to the temperate-zone or tropical lakes, the lakes over the TP can transfer vast heat and water fluxes directly to the middle troposphere, which can further interact with the large scale tropical and extratropical systems during the boreal summer (Yanai et al 1992;Wu et al 2012;Xue et al 2017). Hence, it is imperative to have a comprehensive understanding of the lake-air interactions and the climatic effects of the lake clusters over TP.…”

Historical droughts manifest an abrupt shift to a wetter Tibetan Plateau

“…Although Prep and Temp are the focus of climate change, they cannot directly and effectively reflect the climate wetting and drying of the TP. The TP is a region with the strongest land-atmosphere coupling in the midlatitudes (Xue et al, 2017), where both Prep and Temp are insufficient to account for the impacts of the feedback from the underlying land surface to the atmosphere. Meanwhile, soil moisture (SM) is a pivotal link between the land surface and atmosphere (Wanders et al, 2014).…”