Role of Meteorology and Local Orography on a Flood Event in the Lower Subansiri Basin and Post-Flood Changes to Land Use and Land Cover

The changing characteristics of rainfall over the Brahmaputra Basin during 1998–2018

“…This indicates that overall rainfall is declining everywhere (Deka et al ., 2013; Das et al ., 2015; Jin and Wang, 2017; Kuttippurath et al ., 2021), but high‐intensity rainfall shows distinct patterns with an increase over plains (spatially concentrated) and northwest BB, and decreases over the hilly terrain (especially the wettest regions such as Cherrapunji). These increases in extreme rainfall over the plains can be responsible for floods with a small lead time for evacuation leading to the inundation of massive habitat and agricultural lands, and thus loss of lives (Gogoi et al ., 2020). As mentioned earlier, an increase in excessive rainfall triggered by topographical acceleration can be a very favourable condition for flash floods in the Brahmaputra Basin plains, where mountains surround them on all three sides.…”

“…As mentioned earlier, an increase in excessive rainfall triggered by topographical acceleration can be a very favourable condition for flash floods in the Brahmaputra Basin plains, where mountains surround them on all three sides. In a recent study, exceptionally heavy rainfall intensified by orographic lifting in the hilly regions was shown to have caused a devastating flood in the downstream regions destroying the agricultural productivity by sand aggradation for several cropping seasons (Gogoi et al ., 2020). This asymmetric change in rainfall in the hills and plains may have implications for flooding and hence economic stability of the region.…”

“…info.). Change in Land Use/Land Cover (LULC) plays an important role in modulating the regional radiation budget (Gogoi et al, 2019). Evidence of reduction in Normalized Difference Vegetation Index (NDVI) and change in Leaf Area Index (LAI) over the region is yet another indication of a changing LULC pattern over the region (Figures S5d,S7,suppl.…”

“…It may be noted that the BB presents a very rugged topography with high relief due to the Cenozoic Fold Mountains of the Himalayas and Indo‐Myanmar range that act as a facilitator for frontal or orographic uplift. For example, a recent study found how orography‐induced rainfall in the hilly terrain was responsible for creating floods in the downstream regions of Assam, thereby changing the land use and land cover scenario for several seasons (Gogoi et al ., 2020). Such floods are responsible not only for inundating the low‐lying areas, which are generally agricultural fields, but also for bringing in sands that destroy the fertility of the land for many cropping seasons thereafter.…”