Rapid increase in population and growing demand for agricultural products has generated changes in land use and upland farming systems and resulted in erosion and land degradation over large tracts of northeast India. The spatial variation of soil erosion rates was studied, in a small catchment under a modified form of shifting cultivation on the hilly Meghalaya Plateau, using the 137 Cs technique. Soil erosion and deposition patterns are much influenced by land use. The estimated annual soil loss from cultivated fields ranged from 32 to 79 Mg ha À1 y À1 and reached only 0Á5 Mg ha À1 y À1 from degraded grassland. Calculated soil erosion rates from cultivated fields exceed that which can be produced by weathering of new soil from parent materials. Observed intensification of agricultural production will lead to progressive conversion of cultivated fields into degraded grasslands and other changes to land use in the upper part of the Meghalaya Plateau.

The daily rainfall data for the twentieth century, from three stations across the region, constitute the basis for statistical analysis. However, the low signal-to-noise ratio makes it difficult to find any significant departure from the simplest null hypothesis of the stability of the rain record at individual stations in northeast India. Only the coarsest possible view, i.e. comparing the two halves of the century, provided strongly significant results in the numbers of days with extreme rain. Using a more general approach, the number of Fourier transform extreme amplitudes also differed significantly. Increasingly heavy events during the summer monsoon season, and partly in the pre-and post-monsoon seasons, are offset by a weakening in the winter monsoon season, so that the annual mean rainfall does not show a significant trend over the Meghalaya Hills. Apart from a greater number of years with noticeable extreme rainfall events in the second half of the twentieth century, we can also observe a more pronounced quasi-periodicity of 10-20 and 30-60 days during the same period. The detection of the latter periodicity indicates that the Madden-Julian oscillation plays an important role in the formation of extreme rainfall events over the Meghalaya Hills during extreme monsoon years.

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Multiscale interaction between monsoonal circulation and the local topography causes the southern front of the Darjeeling-Bhutan Himalaya to receive one of the highest annual rainfalls (3000-6000 mm) and most frequent heavy rains (up to 800 mm day -1 ) along the whole southern Himalayan margin. An examination of the patterns of annual rainfall, rainfall concentration, overland flow generation and slope instability indices in the Darjeeling-Bhutan Himalaya for 1986-2015 indicates that the mountain front disturbs rainfall gradient between the Bay of Bengal and the Tibetan Plateau. The results show that the precipitation concentration indices are lowest at the Himalayan front where the annual rainfall and the number of rainy days are highest. The Himalayan front has the highest predisposition to produce overland flow compared to adjacent foreland and the mountain interior. The average probability of the rainfall initialising the shallow landslides increases from 0.6% for a 1-day rainfall threshold of 144 mm to 6.1% for a 4-day rainfall threshold of 193 mm in the study area. The highest probability (up to 10%) of 2-day and longer lowintensity storms at the mountain front indicate that its area is threatened with particularly larger and deeper landslides. The multivariate regression analysis reveals statistically significant linear relationships of rainfall hazard indices with elevation and the distance to the mountain front in the mountain foreland and Himalaya, respectively. Regionally, the Darjeeling Himalaya reveals lower values of rainfall hazard indices, in comparison to the

A hilly catchment (4 km2) was selected to quantify the changes in physico‐chemical soil properties when traditional shifting cultivation is converted to sedentary swidden cultivation (elements of slash and burn cultivation with short fallow period), locally called bun (cropping in rows of raised beds formed from soil), in the central part of the Meghalaya Plateau. Assuming that the monsoonal climate, deep‐weathered granites, and time are relatively uniform over the small catchment, the differences in soil were compared on two contrasting landforms (flat ridges and steep slopes) and three land use types (natural deciduous forest, sedentary swidden cultivation of potatoes, and fallow land with pine forest) within each landform. In contrast to previous studies in region, soil fertility indices calculated in the present study indicated that the bun system can also improve soil quality. Soil response significantly varied at spatial scales, however, and in terms of the possibility of continuing sustainable cultivation in the future. At a local scale on flat terrain upon granites, soil under swidden cultivation had the higher fertility indices, than fallow land and natural forest, whereas steep slope cultivated soil had the lowest fertility indices, following fallow land and natural forest. Therefore, bun system can be efficient in tropical regions with gentle terrain and limited forest resources. At a regional scale, low potato yield combined with a growing food demand forces farmers to expand potato cultivation on steep slopes, the dominant landform in the Meghalaya, increasing the risk of soil degradation. Introducing agroforestry with pine trees into bun cultivation can mitigate the rates of soil degradation on steep slopes.

Correspondence: Piotr Migoń (email: piotr.migon@uni.wroc.pl)The Mylliem granite is one of many igneous bodies within the basement complex of the Meghalaya Plateau, northeast India. Although relatively small in size at c. 90 km 2 , it is very diverse geomorphologically and shows a range of distinctive landscapes within its limits. Relict flat watershed ridges and topographic basins characterize the northern and eastern part of the pluton, whereas to the southwest the relief becomes higher, with steeper hillslopes and deeply incised valleys. Deep weathering and thick saprolites are abundant, as are residual landforms resulting from stripping of the saprolite: domes, tors and boulders. The major reason behind the diversity of granite landscape of the Mylliem pluton is the progress of headward erosion, initiated at the Dauki fault in the south of the Meghalaya. Headward erosion enhances local relief and hence, weathering systems. Multiconcave morphology is gradually transformed into multi-convex one, which is hypothesized to be the specific mode of plateau evolution and scarp retreat in granite bedrock.

Abstract:The estimation of soil erosion rates in complex subtropical agricultural systems of hilly environment is difficult and most of the traditional methods have serious limitations. The 137 Cs technique allows to obtain relatively quickly retrospective medium term soil erosion results. The objective of this study was using 137 Cs approach to quantify soil loss under agricultural system which develops under growing human pressure on the hilly terrain of the Meghalaya Plateau. The measured values of caesium inventory for all sampling points are between 2% and 63% of the reference value of caesium inventory. The estimated annual soil loss for sampling points located on the slope are between 29 and 79 Mg·ha -1 ·yr -1 in the case of an improved mass balance model. It means that soil erosion in this manually tilled agricultural area cannot be neglected.

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