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 Climate over the past Century The main physical triggering mechanism for most of the erosion processes mentioned above is moisture. Although earthquakes can also play a large role in mobilizing various mass wasting processes, they are not nearly as frequent as precipitation and runoff events that area capable of destabilizing a slope. Intense, prolonged monsoon rains and abundant winter snow fall combined with a steep, geologically weak and weathered environment such as the Kullu Valley leads to the activation of a variety of denudation processes. An increase in the magnitude and/or frequency of precipitation or runoff events could potentially lead to higher moisture conditions and likely an increase in the magnitude and/or frequency of erosion processes. However, previous literature and the statistical analysis of a 100-year precipitation record for three urban centers in the valley (i.e. Manali, Nagar, and Kullu town) indicate that there has been no net change in the precipitation amount over the past century (Fig. 3). Although the intensity and frequency of isolated storm events may have changed, the available climatic data precludes any detailed analysis of individual precipitation events. 
Figure 3. Average monthly precipitation at Manali, Nagar, and Kullu over the past century. Grey line indicates the linear trend over the 99 year time period (Source data: Singh, 1995). Changes in temperature may also affect moisture availability. Gupta et al. (1995) indicate that temperatures in the valley have increased, possibly due to environmental climate change. A wetter moisture regime in the valley would result from the accelerated melting of alpine glaciers and more precipitation falling as rain (higher up slope). Potentially, higher runoff fluxes could contribute to an increase in the magnitude and frequency of floods, debris flows, and associated slope failure processes. Nevertheless, according to Sah and Mazari (1998), geomorphic damages to the landscape caused by floods in 1902, 1945, 1988, 1993, 1995, and 1996 are almost identical, only damages to roads, buildings, and other structures have increased. The apparent lack of an obvious hydraulic adjustment by the Beas River and it's tributaries means that either a large portion of the moisture is being evapotranspirated back into the atmosphere before reaching the surface or that the channels themselves are absorbing the impacts of the excess runoff. In either case, the climatic and geomorphological evidence available suggests that the physical environment is not contributing significantly to the reported loss of lives and property as a result of natural hazards. The following section addresses the role played by land use/cover change on the activity and distribution of natural hazard sites over a period of 27 years in the Kullu Valley. Mapping land use/cover As discussed previously, the Kullu Valley has experienced several periods of rapid socioeconomic change, which are reflected in the land use/cover of the area. Land use/cover change analysis in mountain environments focuses mainly on detecting changes between non-built-up and built-up and between forested and non-forested areas. The built-up land use/cover includes not only urban infrastructure within towns and cities, but also individual dwellings, roads linking settlements, and other human-built structures. The stabilizing effect of a forest on mountain slopes has been well documented (Brookes et al., 1997; Ives and Messerli, 1993). The removal of a forest cover from a steep slope often leads to accelerated surface erosion and dramatically increases the chances for landslides as well as runoff. The consequences of deforestation include raised riverbeds due to increased channel siltation, which ultimately leads to more flooding in low-lying areas. Destruction of aquatic habitat and a reduction in the quality of the water, which is an important resource for the local population, are other negative impacts of deforestation. Historical land use/cover maps are often not available for a given region or the required period of time. Historical records, pictures, and oral history provide a somewhat limited and sporadic insight into the land use patterns of the past, if available at all. A common approach to this problem is to use a time series of satellite images to derive historical land use/cover information for the required time period(s). For this research three satellite images from 1972, 1980, and 1999 and a 1999 land use/cover map were used to reconstruct the land use/cover for the past three decades. All three satellite scenes were acquired within the first week of November of each respective year using sensors aboard the Landsat 1 (1972), Landsat 3 (1980), and Landsat 7 (1999) satellites. The autumn acquisition date was selected so as to avoid heavy cloud cover and to maximize the spectral differences between coniferous and deciduous vegetation, the latter of which losses its foliage by mid-October. The 1972 and 1980 scenes were acquired using the 4-band multi-spectral scanner (MSS) sensor, while the 1999 scene was recorded using the 8-band enhanced thematic mapper (E-TM) sensor which has improved spectral and spatial capabilities. All bands were spectrally standardized, geo-registered to UTM zone 43N, and cropped in order minimize differences in reflectance and image geometry. Because the 1999 scene was affected by clouds and cloud shadows over approximately 10% of the area, a cloud/shadow mask was developed and applied to the other two satellite scenes in order to maintain an equal study area size Schanzer (1992). The basis for a supervised classification of the satellite scenes was a land use/cover map and information about locations where land use has not changed appreciably over the past 27 years. |