Spatial and Temporal Variations of Freezing and Thawing Indices From 1960 to 2020 in Mongolia

Abstract

Mongolia is one of the most sensitive regions to climate change, located in the transition of several natural and permafrost zones. Long-term trends in air freezing and thawing indices can therefore enhance our understanding of climate change. This study focuses on changes of the spatiotemporal patterns in air freezing and thawing indices over Mongolia from 1960 to 2020, using observations at 30 meteorological stations. Our results shows that the freezing index ranges from −945.5 to −4,793.6°C day, while the thawing index ranges from 1,164.4 to 4,021.3°C day over Mongolia, and their spatial patterns clearly link to the latitude and altitude. During the study period, the trend in the thawing index (14.4°C-day per year) was larger than the trend in the freezing index (up to −10.1°C-day per year), which results in the net increase of air temperature by 2.4°C across Mongolia. Overall, the increase in the thawing index was larger in the low latitudes and altitudes (e.g., the Gobi-desert, steppes, the Great lake depression and major river valleys) than in high latitudes and altitudes (mountain regions), while it was the opposite for the freezing index. The highest values for both thawing index and freezing index (i.e. the least negative values) have occurred during the last 2 decades. As the trends in the freezing and thawing indices and mean annual air temperature confirm intensive climate warming, increased permafrost degradation and shallower seasonally frozen ground are expected throughout Mongolia.

Fires, Vegetation, and Human—The History of Critical Transitions During the Last 1000 Years in Northeastern Mongolia

“…The mean annual precipitation is 150-300 mm in the north and 50-100 mm in the south (Dagvadorj et al, 2009). Between 1960 and 2020, the mean annual air temperature in Mongolia increased by 2.4 °C (Dashtseren et al, 2021). According to the data from Global Forest Watch, fire season in the country usually starts at the end of March and lasts for about 16 weeks.…”

“…How to understand "dzud"-droughts, snow, and fires According to Hessl et al (2018), the 20th century was one of the warmest periods in Mongolia during the last 1200 years. The warming has multiple environmental implications among which degradation of permafrost seems to be the most vital, however the climatically-induced changes in permafrost in Mongolia are still poorly understood (Dashtseren et al, 2021). Recent study by Hiyama et al (2021) suggest that rising air temperatures and gradual thawing of permafrost in the region cause deeper circulation of groundwater, thereby activating more productive springs.…”

Surface temperature analysis on the eastern shore of Khuvsgul Lake

“…Тухайн Хөвсгөл нуур орчим нь цэвдгийн үргэлжилсэн тархалттай бүсэд багтах бөгөөд байгаль орчны бусад үйл явцад эмзэг мэдрэмтгий төлөв байдалтай байна [9]. Хөвсгөл нуурын зүүн эрэг орчмын цэвдгийн температур нь 10 м гүнд 2006 оны байдлаар -0.3°С-ээс -1.5°С байна хэмээн тогтоосон байдаг [13].…”