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5.1 Flooding in the Tropics (Storm Hydrographs (Land Use When basins are…
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:evergreen_tree: In Humid :evergreen_tree:
Before Storm
- Baseflow present due to regular GW recharge from regular rainfall
During Storm - Surface Runoff
Gentler rising limb
Longer lag time
Lower peak discharge
- Dense vegetation and thick soils encourage infiltration
- High water table encourages saturation, so SOF only reaches the river midway through the storm
- Rise in discharge is later in the storm as runoff takes time to reach channels due to gentler transport limited slopes
- Lower peak discharge as not all rainfall becomes runoff
After Storm - Throughflow
Gentler recession limb
- Throughflow continues to flow into the channel so discharge falls slower
Flooding is a natural hazard, so it is primarily caused by climatic conditions but flood occurrence can be influenced by alterations to the drainage basin due to other natural conditions or human factors. Extent of influence varies across space (humid vs arid) and time (long term impacts of climate change)
:hot_pepper: In Arid :hot_pepper:
Before Storm
- Minimal Baseflow due to little GW flow during dry periods so channels are dry before a storm
During Storm - Surface Runoff
Very steep rising limb
Shorter lag time
Very high peak discharge
- Lack of vegetation and bare grounds with shallow soils and surface crust discourages infil
- Large surface runoff enters channel quickly due to steeper weathering-limited slopes
- Almost all rainfall reaches the channel instantly and discharge rises quickly where peak discharge is reached after peak rainfall
After Storm - Throughflow
Very steep recession limb
- When storm ceases, discharge subsides immediately due to lack of subsurface flows into the channel
- High evpt rates due to high temps so transmission losses
- Permeable channel beds result in percolation so channel discharge falls quickly
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