SAJC Cluster 2 Lecture 7 Notes (Factors Contributing to Fluvial Floods)

St Andrew’s Junior College H2 Cluster 2: Tropical Environments H2_Cluster 2 Lecture 7_2024/pg1 Lecture 7 Floods in the Humid Tropics (I): Factors contributing to Fluvial Floods KEY QUESTIONS: ✓ What factors contribute to fluvial flooding in the humid tropics? With the completion of this lecture, attached readings and tutorial, you should be able to understand the: • Occurrence of fluvial floods when peak discharge exceeds bankfull discharge and inundates adjacent areas that are usually dry • Natural and human factors contributing to occurrence of fluvial floods in the humid tropics Lecture Outline 7.1 Introduction: Floods and related terms 7.2 Causes of Fluvial Floods 7.2.1 Natural factors contributing to fluvial floods. (a) Excessive Rainfall (b) Snow and Ice-melt (c) Features of the drainage basin Box 1: Monsoons, Tropical Cyclones and Flooding in the Humid Tropics 7.2.2 Human factors contributing to fluvial intensify floods. (a) Urbanisation (b) Deforestation (c) Agriculture Box 2: Flooding in KL – caused by human or natural factors? Reading: (1) The 2022 Pakistan floods Natural factors Input (rainfall and/or snowmelt) Drainage basin features (geology & soil, topography, vegetation) Factors contributing to fluvial floods Human factors Urbanisation Deforestation Agriculture

St Andrew’s Junior College H2 Cluster 2: Tropical Environments H2_Cluster 2 Lecture 7_2024/pg2 7.1 Introduction: Floods and related terms • Floods are the most frequent type of natural disaster. This is because of the widespread distribution of river floodplains (see Fig. 1) and low-lying coasts and their long-standing attractions for human settlement. • Floods can cause widespread devastation, resulting in loss of life and damages to personal property and critical public health infrastructure. o According to the WHO, between 1998-2017, floods affected more than 2 billion people worldwide. People who live in floodplains or non-resistant buildings, or lack warning systems and awareness of flooding hazard, are most vulnerable to floods. • There are three common types of floods, of which, for the purpose of this lecture, we shall focus only on fluvial (or river) floods. o Fluvial floods are caused when consistent rain or snow melt forces a river to exceed capacity. (see more later) o Flash floods are caused by rapid and excessive rainfall that raises water heights quickly, and rivers, streams, channels or roads may be overtaken. o Coastal floods are caused by storm surges associated with tropical cyclones and tsunami. • A fluvial flood occurs when river discharge exceeds bankfull discharge, leading to overbank spillage and inundation of land which is not normally sub