Drought

Question

Step-by-step solution

1. Step 1

   Meteorological drought: Defined as a prolonged period of below-average precipitation (rainfall or snowfall) relative to the long-term average for a region. This is the fundamental form of drought from which all others follow. Caused by atmospheric conditions — in particular, persistent blocking anticyclones (high-pressure systems that deflect the normal track of rainfall-bearing weather systems). The UK drought of 2022 resulted from an exceptionally persistent anticyclone over Central Europe blocking Atlantic storm systems through spring and summer. Impact: reduced soil moisture, lower river and reservoir levels.

2. Step 2

   Agricultural drought: Occurs when soil moisture levels fall below what is required for crops and livestock to thrive, even if not all river and reservoir levels are critically low. Agricultural drought typically follows meteorological drought by weeks to months as soil moisture reserves deplete. It can also be triggered by high temperatures that increase evapotranspiration even when rainfall is only slightly below average. Impact: crop failure, reduced yields, livestock death from lack of water and grazing — leading to food insecurity, reduced farmer incomes, and in LICs, famine.

3. Step 3

   Hydrological drought: Occurs when surface water (rivers, lakes) and/or groundwater levels fall well below normal, affecting water supplies for humans and aquatic ecosystems. Hydrological drought lags behind meteorological drought by months or years, because groundwater reservoirs take a long time to deplete — they are filled over decades. Impact: water supply shortages for households and industry; aquatic habitat loss as rivers and lakes shrink; reduced hydroelectric power generation; increased competition and conflict over remaining water resources.

Question

Step-by-step solution

1. Step 1

   Environmental effects:

   (1) Desertification: Prolonged drought kills vegetation and exposes bare soil. Without plant roots to bind it, dry, bare soil is highly susceptible to wind erosion — the topsoil blows away, leaving behind an increasingly infertile, degraded surface. In the Sahel, the desert boundary has shifted southward by 48–200 km in some areas since the 1950s (though the relationship is complex — satellite data shows partial 'greening' during wet periods, demonstrating the vegetation responds dynamically to rainfall).

   (2) Vegetation dieback and loss of biodiversity: Drought-stressed plants die, reducing ground cover. Trees die, removing shade and further increasing surface temperatures and evaporation. Aquatic ecosystems collapse as rivers and lakes shrink — Lake Chad has lost approximately 90% of its surface area since the 1960s due to a combination of reduced rainfall and increased water extraction, eliminating fish habitats and wetland ecosystems.

   (3) Increased wildfire risk: Drought kills and desiccates vegetation, creating large amounts of dry fuel. Lightning-triggered wildfires spread more easily and burn more intensely, destroying remaining vegetation cover and releasing stored carbon.

2. Step 2

   Human effects:

   (1) Crop failure and famine: The Sahel's population is predominantly subsistence farmers and pastoralists, dependent on rain-fed agriculture and grazing land. Drought causes catastrophic crop failures — the 1983-1985 Sahel drought caused widespread famine across Ethiopia, Sudan, Mali, Niger, and Chad, with estimates of up to 1 million deaths from famine (the 'Band Aid' famine that prompted the 1985 Live Aid concert). Grain stores are rapidly exhausted; families cannot afford food imports.

   (2) Livestock deaths: Pastoralists depend entirely on cattle, goats, sheep and camels. Drought destroys grazing land and water sources — livestock die in large numbers, eliminating livelihoods and assets that take years to rebuild.

   (3) Water shortages: Declining groundwater levels, dry river beds, and shrinking lakes leave communities without drinking water. Women and children walk increasingly long distances (sometimes 5–10 km) to find water, consuming time that could be used for education and income generation.

   (4) Conflict and displacement: Competition over scarce water sources and grazing land intensifies between settled farmers and nomadic pastoralists. In the Sahel, conflicts between Fulani herders and Hausa farmers over water holes and grazing rights have escalated into inter-ethnic violence. Drought forces mass migration — environmental refugees leave rural areas for cities or cross international borders.

Question

Step-by-step solution

1. Step 1

   Strategy 1 — Drip irrigation: Conventional irrigation (flood or sprinkler methods) loses 30–50% of water to evaporation and surface runoff before it reaches plant roots. Drip irrigation delivers water through a network of pipes and emitters directly to the root zone of each plant at low flow rates, minimising evaporation and surface runoff. Water use efficiency can reach 90–95%.

   Effectiveness: Very high — Israel has used drip irrigation since the 1960s and reduced agricultural water consumption by 50% while increasing crop yields. Widely used in arid regions from Spain to Australia to India.

   Limitation: High initial capital cost — the pipes, emitters, filters, and automation systems are expensive to purchase and install, making them inaccessible to subsistence farmers in LICs who have the greatest drought vulnerability without external support or credit.

2. Step 2

   Strategy 2 — Desalination: Desalination removes salt from seawater or brackish groundwater to produce fresh drinking water. The two main methods are reverse osmosis (forcing seawater through semi-permeable membranes under high pressure — widely used) and multi-stage flash distillation (heating seawater and condensing the steam — older technology, energy intensive). Saudi Arabia, UAE, Kuwait, Israel, and Singapore all rely heavily on desalinated water.

   Effectiveness: Extremely reliable and scalable — Saudi Arabia produces over 7 million m³ of desalinated water per day. Not dependent on rainfall, so unaffected by drought. Israel meets ~75% of its domestic water from desalination (Sorek plant, world's largest, produces 600,000 m³/day).

   Limitation: Very energy-intensive — currently mostly powered by fossil fuels. Large carbon footprint; reverse osmosis uses 3–10 kWh per m³ of water. Only viable for coastal countries or those with saline groundwater; not usable for landlocked countries. Expensive: cost per m³ ($0.5–2) is 2–5× that of conventional water treatment. Concentrated brine discharged to sea causes local marine pollution.

3. Step 3

   Strategy 3 — Inter-basin water transfer: Water is moved from water-surplus river basins to water-deficit regions through canals, tunnels, aqueducts, and pumping stations — creating an artificial redistribution of freshwater.

   Effectiveness: Can dramatically increase water supply in deficit regions. China's South-North Water Transfer Project (the world's largest water diversion scheme) moves approximately 10 billion m³/year from the water-rich Yangtze River basin to the water-scarce North China Plain, supplying Beijing and other northern cities. California's State Water Project transfers water from northern California to the dry south, supporting agriculture and cities.

   Limitation: Extremely expensive to construct and maintain (China's project cost over $80 billion). Creates ecological impacts on source rivers (reduced flow, altered temperature, sediment starvation downstream). Political conflicts between water-source and water-receiving regions are common (California's north-south water politics; similar tensions between Indian states over river sharing). Does not address the root cause — unsustainable water demand — and may encourage greater water use in deficit areas, worsening long-term scarcity.

Question

Step-by-step solution

1. Step 1

   Physical and human factors making the drought devastating:

   Physical factors: (1) Exceptional severity: The 2006-2010 drought was the most severe in Syria's instrumental record (going back ~100 years). Annual rainfall in the agriculturally important northeastern region (the Jazirah 'breadbasket') fell to 20–40% of normal for four consecutive years — sustained multi-year drought is far more damaging than a single dry year because there is no recovery period. (2) Climate change linkage: Research published in the Proceedings of the National Academy of Sciences (Kelley et al., 2015) concluded that anthropogenic climate change made a drought of this severity 2–3 times more likely in the eastern Mediterranean region, by increasing temperatures (higher evapotranspiration) and reducing winter rainfall. (3) High evapotranspiration: Temperatures in Syria during the drought period were above average, accelerating the drying of soil and reducing crop water availability beyond what rainfall deficit alone would cause.

   Human factors: (1) Over-extraction of groundwater: Prior to the drought, Syrian agricultural policy encouraged deep-well irrigation of cotton and wheat, subsidising diesel fuel for water pumps. This led to massive over-extraction of groundwater — water tables in the northeast fell 15 m between 2002 and 2010. When the drought struck, the groundwater buffer that could have sustained farming was already largely depleted. (2) Lack of drought-resistant crops: Irrigation-dependent commercial agriculture (cotton, wheat) replaced more drought-tolerant traditional cropping systems. When irrigation water became unavailable, entire harvests failed. (3) Government policy failures: Syrian agricultural subsidies were removed beginning in 2008, precisely during the drought, as an IMF-recommended economic reform. Diesel and fertiliser subsidies were cut — reducing farmers' capacity to drill deeper wells or adapt to drought conditions.

2. Step 2

   Sequence of events from drought to conflict:

   (1) Agricultural collapse (2007-2010): Crop failures and livestock deaths affected approximately 800,000 farming families. An estimated 60% of Syrian villages lost their entire harvest; the livestock population in the northeast fell by 85%.

   (2) Rural-urban migration (2008-2010): Approximately 1.5 million people — farmers, farmworkers, and their families — migrated from drought-stricken rural areas (primarily the northeast: Deir ez-Zor, Raqqa, Hassaka governorates) to the outskirts of major cities (Damascus, Aleppo, Homs, Daraa). These migrants settled in informal 'poverty belts' around Syrian cities.

   (3) Urban social pressure (2009-2011): The sudden influx of displaced rural people — many of whom had lost their livelihoods and were food-insecure — into cities that were already experiencing economic difficulties (unemployment rate ~20%, poverty rate ~35% among youth) created concentrated social pressure. These migrants were competing for scarce low-skill urban jobs and public services.

   (4) Political discontent and protest (2011): The combination of drought-induced poverty, economic discontent, government corruption, and political repression provided the social conditions in which the Arab Spring protests sparked mass demonstrations in Syria (beginning March 2011, starting in Daraa — a city that had received many drought migrants from its rural surroundings). The Assad government's violent repression of protests triggered armed uprising.

   (5) Civil war and refugee crisis: Armed conflict beginning in 2011 forced the displacement of approximately 6.6 million refugees by 2016 (UNHCR), primarily to Turkey, Lebanon, Jordan, and Europe — one of the largest refugee crises in modern history.

3. Step 3

   Evaluation — was drought the primary cause of the conflict?

   Evidence that drought was a significant causal factor: (1) The drought demonstrably displaced 1.5 million people to cities, directly creating the concentrated social discontent that manifested as protest. The initial protests were heavily concentrated in areas with high concentrations of drought migrants. (2) The timing is compelling — the worst drought in a century immediately preceded the conflict. (3) The PNAS study (Kelley et al., 2015) established a causal chain: climate change → drought severity → agricultural collapse → rural-urban migration → social stress → conflict trigger.

   Evidence that drought was NOT the primary cause: (1) Political causes were deep-rooted and pre-existing: Syria under the Assad family (in power since 1971) had a long history of political repression, sectarian tensions (Sunni majority vs. Alawi-led government), economic mismanagement, and corruption. Many Syrians were politically alienated long before the drought. (2) The Arab Spring was regional: Revolutions occurred simultaneously in Tunisia, Egypt, Libya, Bahrain, and Yemen in 2010-2011 — many without significant drought. The broader regional political dynamic of Arab Spring clearly played a role beyond Syria's specific conditions. (3) Correlation is not causation: Many regions experience severe droughts without political collapse — Australia, Spain, and the USA have all experienced comparable multi-year droughts without civil war. The drought explains why conditions were especially severe in Syria, but political structures, governance quality, and pre-existing inequalities determined whether drought stress translated into conflict.

   Conclusion: Drought was a significant accelerant and trigger of the Syrian conflict — it sharpened and concentrated pre-existing political, economic, and social tensions rather than being the sole cause. This has broader implications: as climate change increases drought frequency and severity globally, it will interact with pre-existing political vulnerabilities to increase conflict risk in other water-stressed, politically fragile regions (Sahel, Yemen, Iraq).

Question

Step-by-step solution

1. Step 1

   Mechanism of El Niño:

   Under normal (La Niña) conditions in the Pacific Ocean, strong trade winds blow from east to west along the equator, pushing warm surface water westward — building up a pool of very warm water in the western Pacific (near Indonesia and Australia). Cold water upwells along the South American coast (bringing nutrient-rich water to the surface). The warm western Pacific promotes strong convection and heavy rainfall over Southeast Asia and Australia.

   During El Niño, the trade winds weaken (or even reverse). The warm water pool 'sloshes' back eastward across the Pacific — raising sea surface temperatures (SST) in the central and eastern Pacific (near Peru). Convection and rainfall follow the warm water — shifting from the western Pacific to the central/eastern Pacific. This shift in the major heat source and rainfall pattern alters atmospheric circulation patterns globally (teleconnections):

   (1) Walker Circulation (normally driving east-to-west trade winds) weakens. (2) Rising air over the central Pacific suppresses rising air elsewhere — causing sinking, stable air (and drought) over SE Asia, Australia, southern Africa, and NE Brazil. (3) The jetstream over North America shifts poleward, often causing drought in the southwestern USA and Canada.

   El Niño events occur every 3–7 years, typically lasting 9–12 months.

2. Step 2

   Regions experiencing drought during El Niño:

   (1) Southeast Asia and Australia: The most strongly affected regions. Indonesia, the Philippines, and eastern Australia experience significantly below-average rainfall during El Niño. The 1997-98 El Niño caused catastrophic droughts in Indonesia — crop failures, extremely low river levels, and forest fires that burned across Borneo (releasing massive carbon stores and causing an air pollution crisis). Australia's droughts of 2002-03 and 2006-07 were both El Niño-linked.

   (2) Southern Africa: Mozambique, Zimbabwe, Zambia, and South Africa typically experience drought during El Niño events — agricultural production falls, affecting food security across the region. The 2015-16 El Niño caused the worst Southern African drought in 35 years, requiring food aid for 14 million people.

   (3) Northeast Brazil: The semi-arid Nordeste region of Brazil regularly experiences drought during El Niño — reduced rainfall from displaced convection affects a historically poor region already vulnerable to water insecurity.

   (4) India (variable): Historically, El Niño has often (but not always) weakened the Indian summer monsoon — potentially causing agricultural drought in rain-fed farming regions. However, the relationship is inconsistent.

3. Step 3

   Challenges of using El Niño forecasts for drought management:

   (1) Forecast lead time: El Niño can be predicted 6–12 months in advance using sea surface temperature anomalies in the central Pacific (Niño3.4 region) — measured by ARGO floats and satellites. This provides some planning time — sufficient for governments to pre-position food aid and for farmers to choose drought-resistant crop varieties. Australia's Bureau of Meteorology provides seasonal drought outlooks based on ENSO state.

   (2) Forecast uncertainty — not all El Niños are equal: El Niño events vary greatly in intensity (the 1997-98 El Niño was far more severe than 2002-03). The relationship between ENSO and regional drought is probabilistic — El Niño increases the probability of drought in affected regions but does not guarantee it. Some El Niño events produce little drought in Australia; some droughts in SE Asia occur during neutral ENSO conditions.

   (3) Translating forecasts into action: Even accurate seasonal forecasts are only useful if governments, agricultural departments, and farmers act on them. Actions require: sufficient warning time to change cropping decisions (usually 2–3 months before planting season); farmers who trust and receive the forecasts; governments with financial resources to pre-position food aid or subsidise drought-resistant seeds; international humanitarian systems ready to respond.

   (4) Other drought causes: El Niño explains only one type of drought cause. Droughts also occur due to blocking anticyclones (unrelated to ENSO — UK 2022), long-term desertification, groundwater depletion, and climate change trends — none of which El Niño forecasts address. A comprehensive drought management system must monitor all these factors, not only ENSO.