magnitude: responsible for largest recorded floods e.g. Phutkal River floods in India 2015 due to summer monsoon in May washed away 10 suspension bridges, 2 sch buildings

cause rapid snowmelt so meltH2O rushes downstream. debris dam formed by lava flows block drainages & channels. H2O accumulates, breaks dam-> floods

e.g. Eyjafjallajokull's eruption in Iceland 2010 melted glacial ice

form debris dams in confined valleys. surges of H2O into valley might cause floods

replacement of vegetated soils w/ impermeable surfaces e.g. concrete. i>f, cause HOF which flows quickly to channel. interception reduced, impedes infiltration & subsequent percolation. limits soil moisture, groundH2O storages, reduces interception loss. more rain as surface runoff, arrives @ channel quickly & in large vol.s.

small flood peaks may be increased up to 10x. 1:100 year event may double in size w/ 30% paving cover of basin.

insufficient stormH2O drainage following building dev. inadequate design cap of these systems, even in DCs. hydraulically smooth urban surfaces, w/ dense network of impermeable surface drains & underground sewers deliver HOF more quickly to channel. short LT, steep RL, high PD. system unable to cope w/ excessive H2O input-> floods

encroachment of embankments, roads & intrusion of bridge supports reduces width of channel & carrying cap. obstructions e.g. bridges hinder H2O movement, reducing its velocity, encouraging deposition. further reduces carrying cap, increases frequency w/ which high flows overtop banks

frequency: high. could be 6x more numerous than b4 urbanisation

crop roots thinner, shallower, less effective in providing pathways for H2O to infiltrate

soil compaction by tractors & cattle further reduces f

agricultural land drainage: process of draining xs H2O on agricultural land rapidly w/ use of underground drains into rivers. aim is to reduce H2O ponding so land is not too H2Ologged for high productivity farming e.g. clayey soil

drains can efficiently release H2O from field to channels & their presence is linked to an increase in stream density (albeit underground), leading to quick rise in stream discharge during rainstorms-> floods

soil tilling (ploughing) loosens soil, H2O drained likely to contain topsoil, washed away by surface runoff, into rivers, reducing carrying cap

magnitude: usually LDCs, which are heavily dependent on it

magnitude: wherever there is deforestation, increases. in small basins, more than 4x increase in flood peak folds recorded tgt w/ suspended sediment conc.s up to 100x greater than in rivers draining undisturbed forested land

encourages generation of HOF (raindrop impact + loss of roots) w/o roots, erosion, increases deposition, reduces channel cap

e.g. flooding in Bangladesh during summer monsoon season exacerbated by deforestation in upstream Ganges-Brahmaputra River H2Osheds

human-induced global warming exacerbates climatic factors that cause an xs H2O input-> floods. extreme precip events over wet tropical regions v. likely more intense & frequent due to increase in avg temp.

accelerate snow & ice melt. e.g. Chorabari glacier, Himalayas retreating quickly for past 50 years, losing 11% of its SA. caused 2013 flood in Kedarnath, India. >1500 drowned