Hydrological hazards (Droughts)

Unique characteristic of drought in NZ

Usually short lived

Definition of drought

Drier than normal conditions

Are all arid areas in drought

No, an area can be arid, and not be in drought, it is the deviation from average conditions that makes a drought

How do droughts impact LDCs

leads to famine which can lead to death and huge economic loss

How do droughts impact MDCs

Droughts don’t kill people but cause significant economic and agricultural losses

The severity of drought impacts depends on

The nation’s wealth

Multifactorial elements of drought

climate, politics, conflict, energy. Causes and consequences of drought are difficult to isolate and understand

How should drought be viewed

Should be seen as a process not an event (slow onset)

What areas can experience drought

All areas, it’s all relative and about the access to usable water

Why is it difficult to predict droughts

Variability in rainfall patterns (year to year), changes in trends (longer term wetter or drier)

Meteorological drought

Based on rainfall shortfall, does not directly equate to plant stress or a decrease in water resources, depends on region

Minimum duration of rain-free period before considered drought in Bali

6 days

Minimum duration of rain-free period before considered drought in Southern Canada

30 days

Minimum duration of rain-free period before considered drought in Lybia

2 years

Hydrological drought

Low stream flow or ground water levels, brought about when the water reserves available in sources like aquifers, lakes, and reservoirs fall below average levels, occurs slowly

Steps in a drought cycle and how meteorological drought causes hydrological drought

1. 1) Meteorological drought

   1. Prolonged period of poor precipitation

2. 2) Propagation

   1. reduced soil moisture, reduction in ground water, reduction in discharge

3. 3) Hydrological drought

   1. sustained low groundwater, low soil moisture, low discharge

4. 4) Meteorological drought breaks

   1. precipitation improves, improved surface water availability

5. 5) Lag time

   1. time delay between meteorological drought ending and hydrological drought ending

6. 6) Hydrological drought ends

   1. Ground water and soil moisture levels return to normal

Where is the Aral Sea

Central Asia, Kazakhstan, Uzbekistan

What happened with he Aral Sea

Significant river diversions for irrigation (particularly the Amu Dar’ya and Syr Dar’ya rivers, up to 90% in 1960s), water was used for Soviet era central planning and cotton cropping, only 12% of the canals were sealed (incurred high loss of water) causing sea to shrink and salinity to increase

What was the size of the Aral sea by 2007

10% of its original size

How much did salinity increase in the Aral Sea due to diversions

from 10 g/l to 100 g/l (seawater is 35 g/l), caused fishery collapse

What happened to the Aral Sea between 1989 and 1990

It split into two parts (the large and small areas)

What happened to the environment in the Aral Sea

Aquatic ecosystem largely destroyed, environmental toxicity of the exposed lakebed, land was used for weapons testing, industrial projects, was subject to pesticides and fertilizer runoff

What were the social impacts of what happened to the Aral Sea

deflation of salt and sand lead to pasture destruction, unemployment and population exodus, affected the health of 5 million people (spikes in anemia, asthma and typhoid), life expectancy dropped from 64 to 51, 100,000 people displaced

What organization is trying to save the Aral Sea

International Fund for Saving the Aral Sea (IFAS) established by heads of central Asian states (Kazakhstan, Uzbekistan, Turkmenistan, Tajikistan, Kyrgyz)

When was IFAS established

1993

Definition of famine

Famine is a situation in which a substantial proportion of the population of a country or region are unable to access adequate food, resulting in widespread acute malnutrition and loss of life by starvation and disease

How meteorological drought leads to famine

Rainfall deficit → streamflow/groundwater deficit → soil moisture deficit → Food deficit

Milankovitch cycles

Describe the collective effects of changes in the Earth’s movements on its climate over thousands of years. Earth’s orbit around the sun varies between nearly circular and mildly elliptical due to gravitational forces from other bodies. Elliptical orbits cause more variability in the amount of solar radiation. Tilt of the earth also varies slightly which changes intensity of seasons (greater tilt more extreme season)

What are physical factors that change climate and drought probability

Large scale circulation systems are inherently variable which changes climate (can experience variability on short and long scales), Milankovitch cycles,

El Nino Southern Oscillation

The cycle of El Nino and La Nina in the central and eastern tropical pacific, loosely operates over timescales of 1-8 years

El nino

Warm conditions in the tropical pacific (west coast of north and south America) due to weak trade winds letting warm ocean water travel back to that area. Can cause storms and flooding in southern US and sunny dry conditions in Northern US

La nina

Strong trade winds blow warm water west toward Indonesia and Australia allowing cold water to upwell along the west coast of north and south America (eastern pacific), can lead to drought in southern US, and cooler temps, heavy rain, and flooding in north western US

Effects of El Nino in Australia

Low rainfall

Effects of La Nina in Australia

High rainfall

Effects of El Nino in NZ

Summer more westerly, drier east coast

Effects of La Nina in NZ

Summer more NE, wetter east coast

What is the Southern Annular Mode (SAM)

Is a ring of climate variability that encircles the South Pole and extends over New Zealand, involves alternating windiness and storm activity. Has two phases (positive and negative)

Positive SAM

Associated with higher than normal air pressure in New Zealand, brings light winds and tranquil weather conditions, windiness and storm activity is increased over Southern Ocean and Antarctica

Negative SAM

Usually results in lower than normal air pressure around New Zealand and higher pressure well to the south of the country. Cause cooler and wetter conditions in the west of both islands

Human causes of drought

Deforestation, overgrazing, improper water use management, urbanization, high poverty makes areas more susceptible because they don’t have the option to make sustainable descisions

Technological responses to drought

Rainfall seeding (not viable for high populations), groundwater (difficult to manage sustainably), Dams, Shifting water through pipelines and aqueducts (more common in MDCs), Desalinization (expensive and energy intense)

Characteristics of All American Canal

Irrigates 250,000 ha of land, has 8 hydro plants, resulted in 500 deaths

Community-based drought responses and adaptations

Agricultural diversification, increase/decrease livestock in sync, debt for farmers to get through, crop improvement

Predicting and forecasting droughts

Important to understand meteorology and climatology (closely related to drought, some intergovernmental agencies responsible for predicting and forecasting, Importance of early warning and mitigation

Example of an agency that assists with drought

Global Information and Early Warning Systems (GIEWS) — Food and Agriculture organization (FAO) since 1975 improving food security in 22 drought-prone African nations

Sustainable drought practices to deal with droughts

Lower stocking rates, soil conservation measures (cover crops, no till), less intensive land use, use of ponds (artificial recharge or aquifers)

Impact of climate change on drought

The impacts like the Milankovich cycle are predictable but climate change is causing deviations from this cycle. Temperatures are rising and the hydrological cycle is becoming more volatile

Climate change impacts on irrigation and food production

Some regions will be able to produce more food, some will be able to produce similar or more by increasing irrigation, some regions will produce less food, increased conflict over water resources, higher likelihood of agricultural drought and hydrological drought

Hydropower makes up what percent of NZ’s power grid

60%

What is the Waitaki scheme

Is a hydropower scheme consisting of eight power stations along the Waitaki river. Generates enough energy to power about 832,000 average homes annually

What plays an important role in the Waitaki scheme

Spring snowmelt recharges reservoir levels which maintains river levels and energy output

What is New Zealand energy production vulnerable to

Short term variability in precipitation and hydrological drought

Impacts of climate change on climate system and drought

Increased variability in the climate system, potential increased in frequency, intensity, and duration of drought conditions due to changes in thermo-dynamic forcings and land atmosphere feedbacks, reduced precipitation in some regions, increased precipitation deficits due to increase in evaporation in others, weakening of the water cycle, initiation of negative feedback loops that reinforce drought conditions, increases in global land area affected by meteorological drought from 10% in 1990 to 30% in 2025

Where do most famine droughts occur

Africa