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Has the Kullu district experienced an increase in natural hazard activity over the past 27 years?- a case study in risk and land use/cover change
The notion that intensification of land use (e.g. deforestation, urbanization) in mountain environments is rampant and leads to regional-scale degradation of the land and increased flooding of lowland areas has been the focus of many studies (e.g. Eckholm, 1975; Ives, 1987; Hofer, 1993; Ives and Messerli 1993; Lauterburg, 1993). Population growth due to high birthrates, in-migration, and/or improved access to healthcare facilities often necessitate the development of infrastructure such as roads, trails, and buildings and an intensification of agricultural/horticultural, timber extraction (for fuel and building material), and grazing activity. The resulting impacts are purported to have increased the risks associated with landslides, floods, and other erosion processes. Mass wasting, flooding, and increased sedimentation are often seen as direct consequences of the over-population and poor land management practices of the hill-people (Gupta, 1990).
A number of authors (e.g. Hofer, 1993; Lauterburg, 1993) have identified the need for more reliable empirical data and research in order to properly evaluate the role of land use change and increased population on the activity of erosion processes in the Himalaya. Ives and Messerli (1993) warn against extrapolation of local results to the entire Himalayan region and Lauterburg (1993) concludes that the impact of human activity on the landscape in terms of erosion processes is heavily scale-dependent. The lack of reliable data is demonstrated when comparing the results of research carried out by Kuster (1993), who concludes that there has been an increase in the forests of Himachal Pradesh, India and Gupta (1990) who warns of the impending total deforestation of the very same area. There is little doubt that the consequences of increased land pressures are having a negative impact on parts of the Himalaya but care must be taken not to generalize this to the entire region. Micro- and meso-scale differences in climate, geology, vegetation, and human land use all play a role in determining the extent to which human activity affects natural erosion processes.
The Kullu District in the state of Himachal Pradesh, where this research project is focused, has undergone significant land use/cover change and intensification. The Kullu District, like all mountainous areas, is subject to natural processes of erosion such as mass wasting, flooding, and avalanche activity. The extent of economic and human losses due to flooding and mass wasting activity, especially during the previous two decades, is alarming and provides the stimulus for this research. A single flood event in the Kullu Valley in 1993 caused an estimated US$18 million in damages and claimed the lives of 6 people (Sah and Mazari, 1998). A flood of similar magnitude in 1905 caused similar geomorphic damages, but had virtually no direct impact on people or infrastructure. The unchecked expansion of built-up areas into geomorphologically active regions such as the river flood plain, unstable slope deposits, and debris flow fans has been accelerating and is a major cause for concern. The consequences associated with rapid land use change due to uncontrolled development in mountain areas has been studied by Gardner et al. (1997), Singh and Pandey (1996), Gupta (1997), Rao (1997), and Yudhbir (1997). Kuster (1993) and Gardner et al. (1997) assessed the effects of deforestation and urbanization on the state of natural hazards in this area and concluded that:
There is relatively little evidence (to suggest) that human activities have materially altered the frequency, magnitude, and location of hazardous processes so as to increase risk except in a few, very localized situations. The primary causative factors in the increased risk are growth in tourist demand and intensification and diversification of commercial agriculture. Gardner et al. (1997, p.251)
Thus the research question central to this project is to determine the validity of these claims and identify the main driving forces behind the dramatic increase in natural hazard activity. In addition the paper aims to explore the interactions between and consequences of land use intensification, environmental degradation, and activity of erosion processes. The methods employed and developed in this study area are intended to be globally applicable.
Study Area
The Kullu District located in state of Himachal Pradesh, India is in the transition zone between the lesser Himalaya to the south and the greater Himalaya to the north. Elevation of the valley floor rises northward from ~1,100m near Bhuntar to 4,000m at Rohtang Pass with an average relief of ~2,000m (Fig. 1). The temperate climate is characterized by dry winters and hot, rainy summers. Average annual precipitation amounts of more than 4,000mm in the valley are due to the monsoon, which brings persistent rains beginning in June and lasting until late September. Temperatures range from a mean daily minimum of between -15°C and 0°C in January to maximums of 20°C to 30°C in June. Topography plays a key role in modifying the local climate in terms of lower temperatures and higher precipitation amounts on north/northeast-facing slopes.
Geologically the area is composed of predominantly Precambrian phyllites, schists and gniesses, and granite of the Jutogh and Chail Formations (Mehta, 1976). Southern areas of the valley are composed of heavily folded and faulted sedimentary rocks including shales, quartzites, dolomites, and sandstones. Earthquakes continue to play a significant role in reshaping the valley, which falls into the highest category of earthquake risk (zone V). Intense physical weathering is the primary agent of erosion with chemical weathering playing a minor role in the lower elevations. Surficial materials are composed mainly of colluvium, alluvium, and morainal deposits. Soils are of the sub-montane podzolic type with average depths of 50 to 100cm (Singh, 1992). It can be assumed that the geology of the Kullu Valley has not changed appreciable over the relatively short time frame of this research.
Present surface cover consists mainly of forests which cover ~38% of the total land area of the state, agricultural fields account for ~11%, orchards and grazing land each occupy ~10%, 5% of the land is abandoned, and the remaining 25% is regarded as unfit for vegetation (i.e. snow, ice, and rock). The most productive agricultural fields are located on the relatively flat valley bottom and on fans where nutrient-rich alluvial soils are most abundant. Up slope from these are terraces where maize, wheat, barley, and rice are grown. Mixed-in with these fields are orchard terraces, which are typically situated on previously abandoned or less productive soils on the lower to mid-slopes. Grazing and forested areas are typically found above the agricultural fields and orchards, and in some cases extend all the way to ridgeline.
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