Three decades of landslide activity in western Nepal: new insights into trends and climate drivers

Abstract

In recent decades, landslide disasters in the Himalayas, as in other mountain regions, are widely reported to have increased. While some studies have suggested a link to increasing heavy rainfall under a warmer climate, others pointed to anthropogenic influences on slope stability, and increasing exposure of people and assets located in harm’s way. A lack of sufficiently high-resolution regional landslide inventories, both spatially and temporally, has prevented any robust consensus so far. Focusing on Far-Western Nepal, we draw on remote sensing techniques to create a regional inventory of 26,350 single landslide events, of which 8778 date to the period 1992–2018. These events serve as a basis for the analyses of landslide frequency relationships and trends in relation to precipitation and temperature datasets. Results show a strong correlation between the annual number of shallow landslides and the accumulated monsoon precipitation (r = 0.74). Furthermore, warm and dry monsoons followed by especially rainy monsoons produce the highest incidence of shallow landslides (r = 0.77). However, we find strong spatial variability in the strength of these relationships, which is linked to recent demographic development in the region. This highlights the role of anthropogenic drivers, and in particular road cutting and land-use change, in amplifying the seasonal monsoon influence on slope stability. In parallel, the absence of any long-term trends in landslide activity, despite widely reported increase in landslide disasters, points strongly to increasing exposure of people and infrastructure as the main driver of landslide disasters in this region of Nepal. By contrast, no climate change signal is evident from the data.

30-year record of Himalaya mass-wasting reveals landscape perturbations by extreme events

“…Note that we avoid typical measures of monsoon strength such as the SASMI 33 as these are derived over extensive regional scales and so do not capture local changes in monsoon conditions. As previously observed in western Nepal 32 ,we find that for the PERSIANN-CDR data, total MJJAS precipitation provides the best fit to the mass-wasting data (Fig. 2a -d), whilst for APHRODITE, it is total MJJAS precipitation > 25 mm (Fig.…”

“…For the mapped region, we then correlate all measures of mass-wasting volume for pre-Gorkha earthquake years with proxies for ASM strength derived from two rainfall products: PERSIANN-CDR 29,30 and APHRODITE 31 (see methods). For both PERSIANN-CDR and APHRODITE, we use several proxies for ASM strength that have previously been investigated in the literature 3,32 . These proxies are: total May to September (MJJAS) precipitation, total precipitation from 15 th July -end-September, total MJJAS precipitation > 25 mm (sum of all precipitation days with total rainfall values > 25 mm), and total precipitation > 25 mm from 15 th July -end-September (sum of all precipitation days within this time periods with total rainfall values > 25 mm).…”

“…Empirical relationships between ASM strength and mass-wasting can be used to predict how much background mass-wasting is expected to occur each year based on that years ASM strength. Four previously investigated proxies of ASM strength 3,32 , for both the PERSIANN-CDR and APHRODITE data, were correlated with each measure of mass-wasting volume (total and scar volumes (m 3 /km 2 ) of new and reactivated/remobilised landslides ["New + RR"] and of only new landslides ["New Only"]). These proxies were: total grid-averaged MJJAS precipitation, total grid-averaged MJJAS precipitation > 25 mm, total grid-averaged precipitation from 15 th June -September, and total grid-averaged precipitation > 25 mm for 15 th June -September.…”

Natural and human-induced landslides in a tropical mountainous region: the Rift flank west of Lake Kivu (DR Congo)

“…Nevertheless, the current knowledge on landslide processes in these regions remains limited as it is mostly derived from susceptibility models made at continental or global levels (Stanley and Kirschbaum, 2017;Broeckx et al, 2018). Because they are not based on The growing demographic pressure and widespread land use and land cover (LULC) changes are expected to increase the frequency and impacts of landslides in tropical mountainous regions, especially in rural environments DeFries et al, 2010;Mugagga et al, 2012;Guns and Vanacker, 2014;Froude and Petley, 2018;50 Depicker et al, 2021a;Muñoz-Torrero Manchado et al, 2021). Deforestation and the associated loss of tree roots lower the slope stability by decreasing regolith cohesion and altering drainage patterns (Sidle and Bogaard, 2016).…”

“…This increases the landside activity, particularly in the first years following the alteration of the landscape (e.g. Brenning et al, 2015;Arca et al, 2018;McAdoo 55 et al, 2018;Vuillez et al, 2018;Muñoz-Torrero Manchado et al, 2021). However, the exact impact of these anthropogenic factors on landslide processes depends on their timing and other environmental conditions such as slope angle and lithology (Depicker et al, 2021b).…”