The Tibetan Plateau (TP), known as the “Third Pole” and the “world water tower”, hosts the largest ice mass outside the Polar Regions. The glacial melt from this place feeds the largest Asian rivers, such as the Indus, Ganges, Brahmaputra, Yangtze and Yellow River that provides fresh water to more than one-third of the world population.
In recent decades, the TP glaciers have been observed to be altered significantly by variations in not only temperature but also monsoon- and westerlies-derived precipitation, causing considerable concerns of society to potential future variations in this water tower. To what extent the atmospheric circulations, such as the Indian Monsoon (IM) varied over time on the TP is accordingly the hot off the press in climate research, since knowledge of this is crucial for projecting future climate change and associated glacial melt and further attached natural hazards and food security.
Although changes in the intensity of past IM have been inferred in a wide range of studies, our knowledge of that is still limited especially with respect to the rate and magnitude. In a recent paper, we shown that, other than prior suggested gradual variabilities on at least centennial or millennial time scale in response to gradual insolation forcing, the IM could change abruptly and tremendously solely on decadal time scale that possibly triggered by the “switching” effect of the TP from orographic blocking to thermal pulling.
To better assess the behavior of the IM on the TP, a lake, named Taro Co, locating near the recent northern boundary of the IM on the TP, was chosen. The special lake position allowed us to directly examine shifts of moisture sources of the lake catchment over the past three centuries. We consequently observed and highlighted a rapid northward shift of the IM in the lake catchment at the end of the Little Ice Age (LIA).
What about the extent and why the IM shifted? To answer the question, a better choice is to put the observed phenomenon to a large spatial context, and as a result, a synthesis of pre-existing climate records on and around the TP was carried. Following this, we identified that the IM shifted northward at least 1.5º in latitude.
Since no more significant change in solar forcing (insolation or irradiation) over the past three centuries, we attributed this rapid IM change to a “switching” effect of the TP from orographic blocking to thermal pulling linked temperature variations.
The above mentioned rapid northward shift of the IM and recorded interplay between the IM and westerlies over the Tibet, as shown in our study, is of crucial importance to promote our understanding of climate dynamics going from a cooler period (e.g. Little Ice Age) to modern warmer conditions.
The study, Rapid Northward Shift of the Indian Monsoon on the Tibetan Plateau at the End of the Little Ice Age was recently published in the Journal of Geophysical Research: Atmospheres.