Forecast of the development of thermal erosion processes in the Yamalo-Nenets Autonomous Okrug under modern climate changes

Bogatova Dar'ya Maksimovna ORCID: 0000-0002-5883-7343 PhD in Geology and Mineralogy Senior Researcher; Laboratory of Geoecology of the North, Faculty of Geography; Lomonosov Moscow State University 119991, Russia, Moscow, Leninskie Gory str., 1 aleksyutina@gmail.com Other publications by this author     Alyautdinov Ali Raisovich ORCID: 0000-0003-3653-3039 PhD in Geography Senior Researcher, Department cartography and geoinformatics, Faculty of Geography, Lomonosov Moscow State University 119991, Russia, Moscow, Leninskie Gory str., 1, of. GSP 1 ali_alia@mail.ru Zheleznova Irina Vladimirovna ORCID: 0000-0002-4495-8742 PhD in Geography Senior Researcher, Department of Meteorology and Climatology, Faculty of Geography, Lomonosov Moscow State University 119991, Russia, Moscow, Leninskie Gory str., 1, of. GSP 1 ijeleznova@gmail.com Kislov Aleksandr Viktorovich ORCID: 0000-0003-0092-0643 Doctor of Geography Professor, Department of Meteorology and Climatology, Faculty of Geography, Lomonosov Moscow State University 119991, Russia, Moscow, Leninskie Gory str., 1, of. GSP-1 avkislov@mail.ru

Shishov Andrei Aleksandrovich Student, Department of Land Hydrology, Laboratory of Geoecology of the North, Faculty of Geography, Lomonosov Moscow State University 119991, Russia, Moscow, Leninskie Gory str., 1, of. GSP 1 andrej.shishov2015@yandex.ru

Introduction

Erosion processes include the entire complex of denudation processes associated with water flows. Erosion is the linear mechanical destruction of the soil and the removal of the products of this destruction. In the conditions of the development of permafrost, the most dangerous process is thermal erosion – the process of destruction of frozen dispersed rocks due to the simultaneous thermal and mechanical effects of water flows, leading to the embedding of a water stream into a frozen massif with the formation of furrows, potholes and gullies ^[8]. In a more aggressive form, this process leads to the formation of a ravine and therefore the process is called gully thermal erosion ^[7]. 

The main prerequisites for the manifestation of thermal erosion processes can be divided into several groups of factors. Firstly, the key role is played by the geomorphological characteristics of the territory, namely the lengths and slopes of the slopes. Secondly, the lithological and granulometric composition of rocks, as well as their iciness and temperature determine the resistance of the soil to the thermal and mechanical effects of flowing water ^[4]. Thirdly, the amount of precipitation is an important factor, especially precipitation in winter and heavy rainfall in summer. They contribute to a high concentration of runoff in short periods of time, which leads to rapid destruction of rocks and the removal of large volumes of loose material ^[2]. Finally, the fixation of the top layer of soils by plants, especially woody forms (if available), can be considered the main reason that counteracts the development of thermal erosion.

Thermal erosion leads to vertical dismemberment of the relief, disturbance of the soil and vegetation cover and activation of other exogenous denudation processes - landslides, landslides, solifluction, riverbed erosion and others ^[11]. In the conditions of exploitation of territories for mining, accompanied by the construction of engineering structures, prerequisites are formed for increasing the rate of development of thermal erosion due to a reduction in vegetation area, the retention of additional snow masses and an increase in the depth of seasonal thawing under man-made stress ^[12].

Within the Yamalo-Nenets Autonomous Okrug, thermal erosion manifests itself mainly in the Arctic tundra, which is primarily due to the landscape and climatic characteristics of this natural zone – a small amount of phytomass and especially its root system, large water reserves in the snow cover and high water consumption during snowmelt ^[1]. As we move south into the zones of the southern tundra and northern taiga, the length of the thermoerosion ravines and their density decrease sharply, despite the increase in elevation differences and steepness of the slopes.

For the territory of the Yamalo-Nenets Autonomous District, according to the results of climate modeling, by the middle of the XXI century, according to the most "harsh" climate change scenario SSP5-8.5, average temperatures in winter are expected to increase to 4.5 °C and to 2.5 °C in summer, as well as an increase in monthly precipitation in winter by 10% ^[13]. An increase in the depth of the seasonal melt layer, coupled with an increase in river runoff, can lead to an intensive increase in the volume of material removal along the gully network. The degradation of permafrost rocks (MMP) under climate change also contributes to the formation of erosive forms in those areas where previously the soils were densely cemented due to ice-cement, as well as in connection with the thawing of re-vein ice and the development of gully thermal erosion by opening outcrops of underground ice in river and sea coastal ledges.

Research area

The research area is located in the area of continuous permafrost distribution in the north (Yamal Peninsula, Tazovsky and Gydan), in the area of intermittent and insular permafrost distribution in the central and southern parts of the Yamalo-Nenets Autonomous District ^[3]. The spread of MMPs over an area will determine the development of thermal erosion processes, due to their sensitivity to climate change. From the point of view of landscapes from north to south, they change from tundra and forest-tundra to taiga ^[9].

Research methodology

Geological maps, literature data and stock materials were used to identify areas subject to thermal erosion processes and to predict them in case of climate change. The foothill and mountainous regions of the Ural Mountains were not considered in this work. At the first stage, maps were linked in the ArcGIS software package (ArcMap 10.4.1) according to the slope of the surface, the dissection of the relief, the geological structure and the iciness of rocks ^[9]. At the next stage, the mapping of the distribution areas of thermal erosion ravines and re-vein ice was carried out on the basis of modern satellite images (Google Earth). A comparison of time-varying images made it possible to clarify the activity and rate of development of thermal erosion in different parts of the studied territory. The analysis of remote sensing data was compared with linked maps to identify patterns of thermal erosion with a different set of geological and geomorphological factors at the local level.

Next, data on the current state of the climate (temperature and precipitation according to the ERA5 reanalysis data [here you can add a link to the reanalysis and maybe once again to the article in Atmosphere[UzM1] ]) to build links between meteorological characteristics and the intensity of thermal erosion processes. Thus, the dominant factors contributing to the thermal erosion destruction of soils in various parts of the territory have been identified. It should be understood that the increase in summer temperatures and precipitation amounts, of course, accelerates the course of thermal erosion, but in certain areas the heavy granulometric composition of sediments (loams and clays) and small surface slopes prevent its occurrence regardless of climatic conditions.

 Climate changes predicted by 2050 based on the results of climate modeling ^[13] are compared with available data in order to identify areas that are at risk of negative effects of thermal erosion processes in the described perspective. The most dangerous areas are those where a steady increase in temperatures and precipitation is expected with a geological and geomorphological predisposition. The average degree of risk is assumed in areas with an ambiguous combination of landscape conditions and climatic changes, in particular, in areas with intermittent permafrost distribution. A low probability of thermal erosion is associated with areas that are little affected by climate change, as well as with taliks in the valleys of large rivers and other water bodies.

Results and discussion

Currently, thermal erosion processes in the territory of the Yamalo-Nenets Autonomous District are developed everywhere, but with varying intensity (Fig.1). Within the Yamal, Gydan and Taz peninsulas, with a strong dissection of the relief, gully thermal erosion is widespread due to the presence of re-vein ice, the removal of which provokes rapid growth of ravines. The activity of the ravine formation process is significantly enhanced by local interaction with river erosion, which in certain places prepares high steep root banks for the transverse effects of thermal erosion ^[2]. In addition, marine abrasive and thermoabrasion cliffs are also susceptible to destruction due to thermal erosion in perpendicular directions. Significant parts of the Priuralsky, Nadymsky and Shuryshkarsky districts are also classified as high-risk areas, primarily due to the strong dissection of the relief.

Fig. 1. Intensity of thermal erosion processes in the Yamalo-Nenets Autonomous District by 2050

An important factor in the development of thermal erosion processes is man-made interference with natural conditions. Studies in the area of the Bovanenkovsky oil and gas field have shown that the main condition for the occurrence and development of gully thermal erosion is the complete or partial removal of soil and vegetation cover, especially in the form of linear disturbances. On the slopes, this leads to the interception and concentration of dispersed runoff during snowmelt and rainfall, the emergence of temporary eroding flows, which, due to thermal and mechanical effects on frozen, especially sandy, soils, dissect permafrost arrays of dispersed rocks to a depth of 8-10 m. As a result of the occurrence of deep thermal erosion cuts, adjacent areas of the territory lose stability at a distance exceeding 3-4 times the depth of the cut. Such incisions with a length of 100-300 m turn into typical V-shaped ravines within one to two months ^[7]. Thus, climate change, together with a man-made factor, can have catastrophic consequences for the territory due to the development of thermal erosion processes, and the impact is on both natural landscapes and anthropogenic infrastructure.

Purovsky, Krasnoselkupsky and the southern part of the Nadym administrative districts are located in the area of intermittent or insular distribution of permafrost, so climate changes will not affect the thermal erosion processes so much. However, since erosion cuts are one of the ways to drain thermokarst lakes ^[10], and the thermoerosive destruction of the bridge between the lake and the river can lead to a rapid (in 1-2 seasons) descent of the lake, it is impossible not to take into account the possible negative consequences of a local nature.

The analysis of satellite images showed that almost all sections of all rivers in the Yamalo-Nenets Autonomous Okrug have a meandering channel (Fig. 2).

Fig. 2. The meandering bed of the Yuribey River, Yamal

 This type of channel indicates that mainly lateral erosion occurs in it with redeposition of alluvium and with a weakened local depression. Large rivers have branched channels in places, which indicates that accumulation in such parts prevails over erosion. Climate change, accompanied by increased precipitation and rising sea levels, will contribute to further accumulation of material and slow down erosion activity in river valleys, as well as on flat areas. The areas with the lowest intensity of thermal erosion processes relate mainly to the elements of the hydrographic network of the territory – the Ob, Pur, Taz, Nadym rivers and their tributaries. Rivers also act as a local erosion basis for temporary watercourses draining their floodplains and terraces. The study of the actual erosion and riverbed processes associated with sediment transport by river flows is considered in more detail in other works ^[5].

Conclusions

The warming of the Arctic climate is the most important factor determining the dynamics of various natural processes in the region and requiring comprehensive assessments in land use planning, infrastructure construction and the development of individual sectors of the economy. Thermal erosion, as one of the main and most rapid processes of relief formation, can increase many times with loss of soil stability associated with the degradation of frozen rocks, and can cover large areas, threatening the safety of the population and industrial facilities. In the northern part of the Yamalo-Nenets Autonomous Okrug, compared with the present, the activation of thermal erosion may be due to an increase in temperatures and thawing of soils, in the southern part – an increase in precipitation amounts with the already existing discontinuity of permafrost rocks. The proposed scheme of zoning the territory according to the degree of risks is generalized and generalized, since its purpose was to reflect the general features of the development of this process in the presence of generalized data on the dynamics of the main climatic parameters. A more detailed calculation of the rates of thermal erosion in representative areas of the studied territory should be carried out according to field observations and calculation methods based on these data.