Coupling Mechanism of Rural Settlements and Mountain Disasters in the Upper Reaches of Min River

Home , Dujiangyan City, Mao County, Songpan County, Wenchuan County

J. Mt. Sci. (2014) 11(1): 66-72 e-mail: [email protected] http://jms.imde.ac.cn DOI: 10.1007/s11629-012-2366-x

DING Ming-tao1*, CHENG Zun-lan2, WANG Qing1

1 School of Environment and Resources, Southwest University of Science and Technology, Mianyang 621010, China 2 Institute of Mountain Hazards and Environment, Chinese Academy of Sciences, Chengdu 610041, China

*Corresponding author, e-mail: [email protected]

Citation: Ding MT, Cheng ZL, Wang Q (2014) Coupling mechanism of rural settlements and mountain disasters in the uppper reaches of Min River. Journal of Mountain Science 11(1). DOI: 10.1007/s11629-012-2366-x.

Abstract: Human settlements are the place where mechanism; Remote sensing human beings live, among which the rural settlements can be regarded as a reflection of human-land relationship in mountain areas because their vertical Introduction distribution is greatly influenced by the specific geographical environment and ecological conditions Settlement, which refers to residence of all of mountains. Based on field investigation, this paper uses physical, geographical, and ecological theories to kinds for human beings, is composed of physical make a comprehensive study of rural settlements and factors such as constructions, structures, roads, mountain disasters in the upper Min River, which is green lands, and water head sites (Chen and Chen an ecologically fragile area with high-frequency 2002; Wu 2001). Rural settlements, a significant disasters (collapse, landslide, debris flow, etc.) and a spatial form for human beings to survive and live in minority inhabit district. By applying these modern mountain areas, serve as the closest time-space scientific theories, this paper attempts to shed some unit between human beings and mountainous light on the relationship between rural settlements environment (Philips 1998; Chen 2001). Being an and mountain disasters. Consequently, an in-depth important component of regional ecological system, understanding of this relationship was achieved as rural settlement is often the subject matter of follows: (1) Rural settlements and mountain disasters research papers, especially those on the are mainly distributed in the intercepted flows of coordinated development of resource, environment water and soil; and both quantity and quality of arable lands in mountains are important indicators of these and economy in mountain areas. As the upper flows. (2) The Small Watershed Management Project reaches of Min River are a multi-ethnic is a complex system of rural settlements and neighbourhood with typically vulnerable eco- mountain disasters that interacts with and constrains environment and high-frequency mountain the ecological system. By this project, the human disasters, it is of great significance to study survival will be better guaranteed. Being fundamental distribution characteristics of rural settlements and for the ecological reconstruction, the coupling development characteristics of mountain disasters mechanism of rural settlements and mountain there. disasters is not only an engine to promote Rural settlements in the upper reaches of Min harmonious development between human and nature, River are the water source region with high but also a bridge to link them. gravitational potential energy, and thus also have

great value for conservation of soil and water, Keywords: The upper reaches of Min River; Mountain disaster; Rural settlement; Coupling biodiversity and cultural diversity (Liu 2006). Based on field investigation and remote sensing Received: 12 April 2012 image interpretation, the paper focuses on the Accepted: 12 July 2013

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distribution characteristics of rural settlements and the east margin of Qinghai-Tibetan Plateau, the the regularity of mountain disasters there and puts study area serves as the transition zone from the forward some countermeasures. Sichuan Basin towards the Qinghai-Tibetan Plateau. Being high in the west and low in the east, it presents a slope condition from northwest to 1 Study Area southeast in the whole. Characterized by middle and high mountains, it also shows a declining The upper reaches of Min River refer to the topography from northwest towards southeast and reaches above Dujiangyan. Areas covered by the an intensified surface cutting from the north to the tributaries include Wenchuan County, Mao County, south, forming the typical landscape of high Li County, Songpan County, the major part of mountains and crayons. The south-north oriented Heishui County in Aba Tibetan Autonomous longitudinal river valleys are deep, the braes on Prefecture, and a small part of Dujiangyan City. both banks are cliffy, and the canyons vary in terms Located in the northwest Sichuan Basin, east of of relative elevations. Due to the big longitudinal Aba Tibetan Autonomous Prefecture, east area of slope, and the strong capacity of undercut and Qinghai-Tibet Plateau, and east margin of lateral erosion of the river, the dynamic balance of Hengduan Mountain, the study area marks the landscape in the lower river valley is quite fragile. zone of transition from the Sichuan Basin around The study area, which enjoys the azonal arid the mountain and ravine region towards the valley climate, possesses the feature of three- Qinghai-Tibetan Plateau. It’s at 30°45′～33°09′ N dimensional climate in mountains. Due to the and 102°35′～103°56′ E (Figure 1). With a total interleaving control of westerly circulation and length of 337 km, the upper reaches of Min River monsoon warm current, the climate transits in the cover an area of approximately 22,000 km2. horizontal direction from subtropics to warm temperate zone and then to cold temperate zone; in the vertical direction, it demonstrates a climate distribution form of echelonment. Annual mean temperature of the area is 5.7°C～13.5°C, annual precipitation is 400 mm～800 mm, among which 80% is concentrated in the period from May to October. The river valleys have deep incision and big relative elevation difference, warm and moist air flow runs down from the mountain, which is not conducive for the formation of precipitation. As a result, the area enjoys little rainfall and dry climate, which further promotes the formation of dry and hot valleys.

1.2 Social economy

With a population of 388,000 (in 2005), the upper reaches of Min River is not only the largest and exclusive neighbourhood for the Qiang people, but also a backward minority mountainous area. People of the area live along river valleys; and most Figure 1 Location of study area in China and its digital of the population is concentrated in the area of elevation model (DEM). Wenchuan County, Yingxiu Township and Xuankou Township. With major population 1.1 Natural environment distributed on river valleys and mountain terraces, the area’s river valleys are featured by farming Located in the mountain and ravine region on culture, dense population, gathering primary,

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Table 1 Rural distribution and economic development in the upper reaches of Min River, Sichuan Province, China Per capita Land area GDP per capita Nos Nos Nos Village density Counties net income (km2) (RMB Yuan) town village household (km-2) (RMB Yuan) Songpan 8,323 5,780 1,425 25 142 11,640 0.017 Heishui 4,165 2,656 1,029 17 124 10,950 0.021 Mao 4,064 3,748 1,222 23 152 19,219 0.037 Li 4,313 6,016 1,112 13 81 8,176 0.016 Wenchuan 4,083 11,262 1,679 14 126 16,515 0.031 Study area 24,948 5,892 1,293 92 625 66,500 0.025 secondary and tertiary industries of the entire area. 5) in the study area. The high canyon and plateau regions, which are characterized by animal husbandry, enjoy vast land and small population. With minority people of Han, 3 Distribution Characteristics of Rural Zang, Qiang and Hui residing there, it is an area Settlements with diverse economies and cultures. Currently, there are 625 administrative villages and 66,500 By field investigation and RS image peasant households with the density of 0.025 km2, interpretation, it has been found out that there are demonstrating a settlement character of dispersion, 1,667 natural settlements (Figure 2), belonging to low density and small scope (Table 1). 625 administrative villages in study area. In addition, we also obtained data regarding geographical positions, scales and national 2 Data Source composition of the natural settlements, laying foundation for the in-depth analysis in the 2.1 Field investigation

The field investigation was started on April 12th, 2010 in Wenchuan County and ended on October 8th, in Songpan County. We investigated counties of Wenchuan, Li, Mao, Heishui and Songpan in the study area. We also got an overall understanding of rural settlement distribution laws of the area by making on-the-spot surveys and combining related data provided by departments such as territory, water conservancy and construction etc.

2.2 Remote sensing data

The paper applies SPOT 5 (Two resolution ratios of 2.5 m and 10 m; 2009) and SPOT 4 image (Panchromatic resolution ratio of 10 m; 1999), which basically covers the whole study area. In addition, it also supplements and utilizes remote sensing images in Google Earth (SPOT 5 and SPOT 4 images, 10 m; 2010). We plan to analyze the changes of rural settlements and mountain disasters in 10 Figure 2 Distribution maps of rural settlements in the upper years from 1999 (SPOT 4) to 2009 (SPOT reaches of Min River, Southwest China.

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subsequent chapters. in the northwest along Zagu’nao River, mountains in different regions have distinct maximum 3.1 Hypernormal vertical distribution of precipitation elevations. In the downstream area of rural settlements Xuecheng and Tonghua, the maximum precipitation elevation is around 3,000 m above From a global perspective, population sea level, namely, in the 200~300 m of upper limit distribution usually declines with rising of of settlement distribution. Generally speaking, elevation. Similar laws are supposed to exist in the areas with the maximum precipitation are also the settlement distribution (Cohen and Small 1998; place with the most intensive forest distribution, Guo et al 1998). However, judging from the results which means that upper limit of settlement of field investigation, only a small portion is distribution in mountainous areas will be located in distributed along the river valley, while the the areas 200~300 m below those with intensive majority of settlements between 2,000 and 2,800 forest distribution. m above the sea level (Figure 3). The reason is that zones of 2,000 m below the sea level are primarily drought river valleys, while low and middle mountains enjoy warm weather. Southeast and southwest warm-moist air flow is separated by high mountains (Qionglai and Minshan Mountain) and is hard to enter the river valley area. As a result, the study area enjoys dry climate as well as little precipitation with the annual amount of 400~600 mm. Meanwhile, drought of the river valley area is intensified by high mountains, deep valleys, great diurnal temperature variations, significant foehn effect as well as strong valley winds. Therefore, current settlement distribution in the upper reaches of Min River is formed.

3.2 Close relationship with topography, landform, and forest distribution

Take Zagu’nao River of Li County as an example. Elevation of river valley in the drought area is approximately 1,400~1,500 m above the sea level, and upper limit of settlement distribution is around 2,700~2,800 m. The even higher zones with big gradient and cliffy state are not suitable for human beings to live. The trend that upper limit of settlement distribution increases with rising of Figure 3 The A-A’ terrain profiles in the upper reaches elevation for river valleys is related to not only local of Min River, Southwest China. topography and landforms, but also local climate condition and vegetation distribution (Xing et al 3.3 Consistency with the cultivated land 2007; Adekunle et al 2007). For instance, the high distribution canyon region of different reaches has natural conditions not conducive for human residence; to In Zagu’nao River Basin of Li County, a part of name a few: high mountains, cliffy slopes, barren cultivated lands are distributed on fluvial outwash lands and frigid climate etc. In addition, in spite of terrace at the bottom of river valley; and most of the trend that precipitation increases with rising of them in the so-called high middle-level mountain elevation from downstream in the east to upstream gentle slopes over 300~600 m away from the

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valley. The slopes have an elevation of Table 2 Area of farming land and number of 2,000~2,900 m. According to the investigation of settlements with different altitude in Li County, Sichuan Province, China. Area: hm2. Agricultural Bureau of Li County, there distributes 66.0% of the cultivated lands and 78.8% of Items <2,000 m 2,000~2,600 m >2,600 m Area 566.72 2,297.17 614.40 settlements (Chen et al 2004). Compared with the Nos river valley, the slopes enjoy a weaker foehn effect, settlement 58 146 102 smaller ground evaporation as well as milder Area/ dryness of air and soil. In the aspect of climate, Nos 9.77 15.73 6.02 they form a semi-humid region, marking the settlement concentrated distribution area of cultivated lands active tectonics, large elevation difference, and (Table 2). In regions with high mountains and steep terrain are favorable for the development of crayons, due to the limitation of geographical debris flows. Landslides, debris flows, and other environment, there is restricted space for human geological disasters often occur in such areas activities. Generally speaking, cultivated lands and including regions along the upper reaches of Min settlements are witnessed to distribute in identical River below Zhenjiangguan of Songpan County, areas (Daniel and Kenneth 2006). In other words, Heishui River below Luhua Township, Heishui rural settlement distribution shows consistency County and Zagunao River below Shaba of Li with that of cultivated lands. County (Figure 4).

4 Distribution Characteristics of 4.2 Distributed in the areas with abundant Mountain Disasters rainfall and frequent storms

Selecting 246 debris flow gullies and 97 High-intensity rainfall, especially rainstorms, landslides which are representative and large, the is a major motivating factor for landslides and paper emphasizes and analyzes the distribution debris flows. These disasters, therefore, frequently and development characteristics of landslide and occur in regions with abundant rainfall and storms. debris flow, with the support of field investigation Although precipitation in the study area varies, it on mountain disasters in the study area from mainly concentrates in the period from May to April to October, 2010, SPOT5 remote sensing October, accounting for 80%~85% of the annual image interpretation, distribution and risk degree total; and is positively correlated with the maps of debris flows and landslides in Sichuan mountain disaster occurrence. and Chongqing (1: 1,000,000), and so on (Table It is commonly believed that where there is 3). abundant rainfall or abnormal climate, there are more mountain disasters. According to statistics, debris flows, landslides and collapses happened in 4.1 Distributed in the areas with strong rainy season account for 90% of the total. As for river cutting effect and large elevation difference the study area, mountain disasters are also concentrated in the regions with abundant rainfall River-cut areas with strong crustal uplift, and frequent storms.

Table 3 Statistical table of debris flow and landslide in the upper reaches of Min River, Southwest China Counties Nos debris flow Nos landslide Distribution range Wenchuan 56 24 On both sides of the river and its tributaries of Min River Li 87 14 On both sides of the river and its tributaries of Zagu’nao River Mao 41 48 On both sides of the river and its tributaries of Min River Heishui 29 3 On both sides of the river and its tributaries of Heishui River Songpan 33 8 On both sides of the river and its tributaries of Min River Total 246 97

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4.3 Distribution consistency of landslide used in the river valley bench and slight grade zone and debris flow of mid-levels region. The scale of valley terrace settlements is comparatively large because of the Intimate correlation exists between debris better soil quality, richer water resource and higher flows and landslides in the study area, especially in crop output. The development of settlements in the Zagu’nao Basin below Li County and the main mid-levels is influenced by low soil organic matter stream of Min River from Mao County to content, restrictive factors to agricultural Wenchuan County (Figure 4). Landslides and productivity, low and unstable agricultural collapses there provide lots of solid materials for production. In the gentle slope region of high-mid the debris flow occurrence; and bigger ones can mountains, which is also named as the “high mid- even cut off rivers, leading to floods and debris level region” by local people, a lot of arable and flows in the lower reaches. In this manner, a thick soil layers have laid a solid foundation for vicious disaster cycle is created. settlement development. The number and scale of mountain disasters are closely linked with the range of human activities, whose main form there 5 Coupling Mechanism between Rural Settlements and Mountain Disasters is agricultural planting. The development of rural settlements is restricted by both quantity and quality of arable lands. In this manner, rural A systematic analysis of environmental settlements, mountain disasters, quantity and mechanisms of rural settlement formation in the quality of arable lands constitute a contradictory upper reaches of Min River was done from the and comprehensive system. viewpoint of geography and ecology. Using the distribution map of rural settlements (Figure 2) and that of mountain disasters, the distribution map of rural settlements and mountain disasters (Figure 4) was obtained by coupling relationship analysis. Based on field investigation, we can find that there is a kind of coupling relationship between rural settlements and mountain disasters in the study area: (1) To some extent, the kind of mountain disasters that a rural settlement will face is mainly decided by its location. For example, rural settlements in the high canyon region are facing the threat of collapses; those in the middle-and-high regions are threatened by collapses and landslides; and others in river valley by debris flows. (2) Settlements located in the high canyon region are often characterized by social closure, autarkical natural economies, and subsistence agriculture. Such a situation explains why ploughs are the major means of livelihood. Take the Zagu’nao River Basin in Li County Figure 4 Distribution maps of rural settlements and mountain as an example. Ploughs are prevailingly disasters in the upper reaches of Min River, Southwest China.

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(3) A small watershed is not only a basic slopes: approximately half of the farmlands are on natural geographic unit, but also a soil erosion slopes with a gradient larger than 25°, and only control one. The Small Watershed Comprehensive 20% smaller than 15°. Inevitably, these steep-slope Control Project is a complete ecological system farmlands are facing the threat of serious soil-and- concerning interactions and mutual constraints water loss and mountain disasters. Therefore, by between rural settlements and mountain disasters. seizing the opportunities of the Western Mountain residents can get matter and energy for Development Strategy and following the state survival through this project (Wang 2007). project of ecological construction, the conversion of croplands into forests and grasslands should be 6 Discussions actively continued in the upper reaches of Min River so as to increase the forest coverage and Along with the increasing population and decrease the mountain disaster occurrence. human activities, the rural settlement ecosystem of (2) Small villages on steep slopes, especially study area has been faced with more severe those comprised by single person households ecological and economic problems, such as decline should be relocated in river valleys or other of farmland quality, reduction of settlement settlements with better environmental conditions. vegetation, shortage of firewood and water, and the Such ecological relocation will not only reduce the increasing poverty-stricken population. Abnormal human pressure on environment, promoting the geological disasters (earthquake, landslide, debris local ecological and natural environment recovery; flow, collapse, etc.) and climate events (drought, but also cut down government subsidies for the rainstorm, hailstone, gale, etc.) may cause poor and investments in the mountainous degradation or breakdown of the settlement infrastructure maintenance. ecosystem at any time. Besides stop cutting natural forests and other territorial protection measures, Acknowledgment we must adopt appropriate countermeasures at the settlement ecosystem level, so as to solve the above The study was financially supported by the problems. National Natural Science Foundation of China (1) In the spirit of thoroughly and actively (Grant No. 41101164 and 41371185), Directional implementing the state project of ecological Project of Institute of Mountain Hazards and construction, the steep-slope croplands around Environment of Chinese Academy of Sciences settlements should be gradually restored to forests (Grant No. SDS-135-1204-01), and the key project or grasslands. As a matter of fact, the farmlands in of Education Department of Sichuan Province the study area are mainly distributed on steep (Grant No. 13ZA0160).

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