HYDROLOGICAL PROCESSES Hydrol. Process. 17, 3181–3193 (2003) Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/hyp.1382 The influence of climatic change and human activity on erosion processes in sub-arid watersheds in southern East Siberia Leonid M. Korytny,* Olga I. Bazhenova, Galina N. Martianova and Elena A. Ilyicheva Institute of Geography, Siberian Branch of the Russian Academy of Sciences, 1 Ulanbatorskaya St., Irkutsk, 664033, Russia Abstract: A LUCIFS model variant is presented that represents the influence of climate and land use change on fluvial systems. The study considers trends of climatic characteristics (air temperature, annual precipitation totals, rainfall erosion index, aridity and continentality coefficients) for the steppe and partially wooded steppe watersheds of the south of East Siberia (the Yenisey River macro-watershed). It also describes the influence of these characteristics on erosion processes, one indicator of which is the suspended sediment yield. Changes in the river network structure (the order of rivers, lengths, etc.) as a result of agricultural activity during the 20th century are investigated by means of analysis of maps of different dates for one of the watersheds, that of the Selenga River, the biggest tributary of Lake Baikal. The study reveals an increase of erosion process intensity in the first two-thirds of the century in the Selenga River watershed and a reduction of this intensity in the last third of the century, both in the Selenga River watershed and in most of the other watersheds of the study area. Copyright 2003 John Wiley & Sons, Ltd. KEY WORDS LUCIFS; Yenisey watershed; fluvial system; climate change; land use change; river network structure; erosion processes. INTRODUCTION The main part of the paper is concerned with the results of studies of the influence of both climatic change and different anthropogenic impacts on erosional activity in watersheds in southern East Siberia. This study area lies within the Yenisey River basin and attention focuses primarily on small watersheds with steppe vegetation. The indicators of erosion activity considered are the suspended sediment load and the characteristics of the river network structure. First, we outline the conceptual framework for the study. FLUVIAL SYSTEMS AND THE LUCIFS MODEL Watersheds and fluvial systems The left part of Figure 1 comprises a natural system and includes a fluvial system representing the interaction of water (the hydrosphere) and the relief. The other components and characteristics of the natural system are considered as external to the fluvial system. Fluxes of water, solid and dissolved material (including the main organic elements, viz. carbon and phosphorus) are produced within a fluvial system; and the total flux has been termed by Alekseyevsky (1999) as a geo-flow. Within a watershed, budgets for water, sediment and dissolved substance can be established, and this is one of the main reasons for applying the watershed concept in environmental management (Korytny, 1991). * Correspondence to: Leonid M. Korytny, Institute of Geography, Siberian Branch of the Russian Academy of Sciences, 1 Ulanbatorskaya St., Irkutsk, 664033, Russia. E-mail: [email protected] Copyright 2003 John Wiley & Sons, Ltd. 3182 L. M. KORYTNY ET AL. NATURAL COMPLEX SOCIAL - ECONOMIC SUBSYSTEM CLIMATE POPULATION PRODUCTION LITHOSPHERE VEGETATION TRANSPORT INFRASTRUCTURE FLUVIAL SYSTEM LAND USE (HYDROSPHERE + RELIEF) direct influence indirect influence FLUXES OF processes within the fluvial system WATER SEDIMENTS CARBON PHOSPHORUS inverse connections Figure 1. The influence of climatic change and land use on fluvial systems. A LUCIFS model variant In addition to the natural environment, the global system also includes the environment modified by human activity, i.e. settlements, industries, agricultural lands, etc. that, together with people themselves, form a social–economic subsystem of the global environmental system. This is shown in the right-hand part of Figure 1 in relation to a watershed. It is important to emphasize that the social-economic subsystem is an important and equal, but nevertheless special, part of the watershed system, and its influence on the natural system is different from exclusively natural influences. Thus, a watershed is a complex, heterogeneous, but strictly hierarchically organized entity, consisting of many elements interconnected with each other and with many processes constantly changing through time, of which the central ones are the processes operating in the fluvial system. The watershed elements are united in a single unit, first of all by a unidirectional geo-flow, both downslope and down the thalweg. A watershed is a quasi-cybernetic system with many direct and reverse linkages. As a result, any change within the watershed, e.g. forest clearance on the divide, will inevitably be reflected in the functioning of many components of the fluvial system via transformation of material fluxes. The LUCIFS model The main goal of the LUCIFS project is to improve understanding of watershed response to climatic and land-use change. Existing understanding is still insufficient and does not permit reliable prediction of future changes. To attain this goal it is necessary, first of all, to develop a unified investigational framework or approach. Figure 1 presents a LUCIFS model variant that combines concepts of a watershed, a fluvial system and the human impact noted above. Climatic change can influence a fluvial system both directly and via other components of the natural complex (lithosphere, vegetation) and even in a more complex manner via land-use structure changes. Also, land use may be influenced by changes in the lithosphere and vegetation Copyright 2003 John Wiley & Sons, Ltd. Hydrol. Process. 17, 3181–3193 (2003) EROSION PROCESSES IN SOUTH EAST SIBERIA 3183 components, as well as by processes within the social–economic subsystem. In their turn, those processes may influence natural (including climatic) changes (e.g. the greenhouse effect due to increase of anthropogenic CO2 emissions). Although it is not always necessary to observe all sets of impacts and their results, it is important to recognize the complex interactions between elements and factors within a watershed. CLIMATIC CHANGES IN STEPPE AND PARTIALLY WOODED STEPPE REGIONS AND ITS INFLUENCE ON EROSION PROCESSES Methods of analysis Global climate warming impacts many natural processes. Numerous publications have noted changes in the temperature regimes of soils and the land surface and in the extent of permafrost and glaciers, water-level fluctuations in seas and lakes, river flow fluctuations, and vegetation changes. Erosion processes are also sensitive to climatic fluctuations. Significant changes in these processes could be expected within the sub-arid belt of the steppes and partially wooded steppes of southern Siberia, which are distinctive for their continental climate and well-developed relief. The steppe belt included in this study is situated mainly in the Yenisey River watershed, and extends from the west to the south for almost 2000 km. It is characterized by significant landscape, climatic and geomorphological diversity and highly dynamic processes. The belt is subdivided by mountain ranges into separate areas (Figure 2) that are characterized by distinctive fluvial system structures and functioning related to both the local conditions and the location within the belt. Natural complexes of partially wooded steppe, steppe, dry steppe and desert-steppe can be distinguished. As a result of analysis of climatic indicators (temperature and moisture availability, aridity, continentality), a sequence of morpho-dynamic systems ranging from moderately continental partially wooded steppe to extra- continental desert-steppe can be distinguished (Table I). Each is characterized by a distinctive functioning mode, which is expressed in a successive change of the system states. The common uniting characteristic Table I. The main climatic indicators of natural complexes in southern Siberiaa Natural Climate Region Annual Annual change Aridity Continentality complex change in in average index coefficient type average air long-term temperature precipitation (°C) total (mm) T1 T2 r1 A1 A2 K1 K2 Partially wooded Moderately Krasnoyarsk– C0Ð8 C0Ð8 462 0Ð65 0Ð64 56 50 steppe continental Kansk Sharply continental Angarsky 2Ð7 1Ð7 391 0Ð60 0Ð64 70 65 Selenginsky 2Ð4 1Ð6 370 0Ð62 0Ð74 78 73 Foothills-steppe Moderately Koybalsky C0Ð8 C1Ð8 452 0Ð65 0Ð75 54 49 Steppe continental Minusinsky 0Ð5 C0Ð7 337 0Ð85 1Ð01 59 55 Barguzinsky 2Ð8 2Ð6 327 0Ð68 0Ð64 77 76 Selenginsky– 0Ð5 C0Ð1 345 0Ð78 0Ð82 71 65 Khiloksky Dry steppe Sharply continental Udinsky 2Ð6 1Ð5 280 0Ð82 0Ð98 79 74 Desert steppe Moderately Priolkhonsky 1Ð0 0Ð6 212 1Ð22 1Ð28 53 – continental Extra-continental Kyzylsky 4Ð5 2Ð4 253 0Ð75 1Ð19586 Ubsunursky 5Ð5 4Ð4 223 0Ð76 0Ð91 96 87 a Subscripts ‘1’: average long-term data. Subscripts ‘2’: data from 1966 to 1996. Copyright 2003 John Wiley & Sons, Ltd. Hydrol. Process. 17, 3181–3193 (2003) 3184 L. M. KORYTNY ET AL. Figure 2. Trends of (A) average annual air temperature and (B) annual precipitation totals and erosion processes (B) for the steppes and partially-wooded steppes of Siberia over the period from 1966 to 1996. The positive linear temperature trend (°C year1): (a) less than 0Ð02; (b) 0Ð02 to 0Ð04; (c) 0Ð04 to 0Ð06; (d) 0Ð06 to 0Ð08. The negative (f) and positive linear precipitation trend (mm year1): (g) 0 to 1Ð0; (h) 1Ð1 to 2Ð0; (i) 2Ð1to3Ð0,