Fig. 47.1 shows a diagram of the causes and effects of drought in a semi-arid region. Drought is an extended period of below-average rainfall that leads to ...

(a) Three causes of drought [3]

1. Reduced rainfall: Prolonged periods of below-average precipitation deplete soil moisture, rivers, lakes, and groundwater reserves. When rainfall is significantly below the long-term average for an extended period, water supplies cannot meet demand. [1]
2. High temperatures: Excessive heat increases the rate of evaporation from soil, lakes, and rivers, and increases transpiration from plants, causing the land to dry out faster even when some rainfall occurs. Water is lost to the atmosphere more quickly than it can be replenished. [1]
3. Deforestation: Removal of trees reduces transpiration and the recycling of moisture back into the atmosphere. Trees act as biological pumps, drawing water from the soil and releasing it as water vapour, which contributes to cloud formation and subsequent rainfall. Without this recycling, regional rainfall can decrease. [1]

(b) The chain of effects from drought to human migration [4]

1. Water scarcity: Drought causes water scarcity, meaning there is insufficient water for drinking, livestock, and irrigating crops. Rivers dry up, wells run low, and reservoirs are depleted. [1]
2. Crop failure: Without adequate water for irrigation, crops wither and die. Rain-fed agriculture is particularly vulnerable, and farmers have no alternative water source. Livestock also suffer from lack of drinking water and the disappearance of grazing pasture. [1]
3. Famine: Prolonged and widespread crop failure leads to famine, where communities cannot produce or purchase enough food to sustain themselves. Food prices rise sharply as supply falls, putting food beyond the reach of the poorest households. [1]
4. Migration and displacement: Faced with famine, depleted water supplies, and no viable livelihood, people are forced to migrate to other regions or to cities in search of food, water, and employment. This displacement can be temporary or permanent depending on the severity and duration of the drought. [1]

(c) How deforestation can contribute to drought [3]

1. Trees and the water cycle: Trees play a crucial role in the local water cycle by absorbing water from the soil through their extensive root systems and releasing it into the atmosphere through transpiration from their leaves. A single large tree can transpire hundreds of litres of water per day. [1]
2. Reduced moisture recycling: This transpired moisture forms clouds that produce rainfall over the region. When large areas of forest are removed, the amount of moisture recycled into the atmosphere through transpiration is dramatically reduced, leading to fewer clouds and less rainfall downwind. [1]
3. Drier conditions: Without this moisture recycling mechanism, the local and regional climate becomes drier. Deforested land also absorbs more solar radiation (darker exposed soil versus reflective canopy) and has reduced capacity to retain soil moisture, making the area increasingly prone to drought conditions. [1]