Flood and drought susceptibility zonation in the mountain environment: a case study of Upper Siang district, Eastern Himalayas, India

The intensity and frequency of extreme hydrological events are on the rise due to changing climate, and it is pertinent to identify the areas which are likely to suffer from such calamities. This study examines flood and drought susceptibilities in the district with a specific focus on two urban areas—Tuting and Yingkiong. To understand susceptibility enabling conditions, the study attempts an analysis of the recent climatic trends (1991–2021) in Upper Siang district employing regression analysis, Kendall tau, and Box and Whisker plots. Results reveal a general rise in the precipitation (26.42 mm/year) as well as in the temperature (0.032 °C/year) of the study area. Susceptibility is assessed based on analytic hierarchy process and using nine physical parameters viz., absolute relief, slope, drainage density, distance from streams, soil type, topographic wetness index, normalised difference vegetation index, and land use land cover. These layers are integrated to create flood and drought susceptibility maps. About 1.82% area of the Upper Siang district is highly susceptible to floods, whereas over 27% area falls under the high risk of droughts. Even though both the towns lie on the riverbank, Tuting is more prone to floods primarily due to its location on the inner concave side of a meander bend and relatively flat terrain, whereas Yingkiong is relatively safe because it lies on an elevated river terrace. Conversely, areas of the district above 2500 m a.s.l. are highly prone to droughts because of poor accessibility to water resources. It is found that the constrained and meandering valleys are more prone to floods, while steep slopes and ridgeline areas are more prone to droughts. Appropriate region-specific management options can reduce the susceptibility to extreme events in mountainous terrains. Therefore, owing to diverse topography, a region-specific physiographic approach is required in hilly environments for efficient mitigation of the impacts of extreme events.