Theme 7: Drought

LWR 314Prof Sue Walker

Summary

• What is drought?Definitions

• Planning for Drought10 step plan

• Monitoring DroughtIndices

• Predicting droughtSeasonal forecastsLong-term Rainfall analysis

• Mitigation of droughtWater conservation

What is Drought?

• It is a normal, recurrent feature of climate. • occurs almost everywhere, but features vary from region to

region. Defining drought is therefore difficult - • it depends on differences in regions, needs, and disciplinary

perspectives. • many definitions in the literature, • for example,

– drought in Libya occurs when annual rainfall is less than 180 mm, – but in Bali, drought occur after a period of only 6 days without rain!

Drought is an insidious (inconspicuous but harmful) hazard of nature. • Whatever the definition, it is clear that drought cannot be

viewed solely as a physical phenomenon.

What is drought?

Definitions – a) Meteorological droughtb) Agricultural droughtc) Hydrological droughtd) Socio-economical drought

Drought DefinitionsMany definitions, • Originates from a deficiency of precipitation over an extended period of time,

usually a season or more. This deficiency results in a water shortage for some activity, group, or environmental

sector.• should be considered relative to some long-term average condition of balance

between precipitation and evapotranspiration (i.e., evaporation + transpiration) in a particular area, a condition often perceived as “normal”.

• also related to timing (i.e. principal season of occurrence, delays in the start of the rainy season, occurrence of rains in relation to principal crop growth stages) and the effectiveness (i.e., rainfall intensity, number of rainfall events) of the rains.

• Other climatic factors such as high temperature, high wind, and low relative humidity are often associated & can significantly aggravate its severity.

Whatever the definition, it is clear that drought cannot be viewed solely as a physical phenomenon.

=> both conceptual and operational definitions

Definitions – conceptual

Conceptual Definitions of Drought• formulated in general terms, to help people understand the

concept of drought– For example: Drought is a protracted period of deficient precipitation

resulting in extensive damage to crops, resulting in loss of yield.• important in establishing drought policy

– For example, Australian drought policy incorporates an understanding of normal climate variability into its definition of drought. The country provides financial assistance to farmers only under “exceptional drought circumstances,” when drought conditions are beyond those that could be considered part of normal risk management. Declarations of exceptional drought are based on science-driven assessments. Previously, when drought was less well defined from a policy standpoint and less well understood by farmers, some farmers in the semi-arid Australian climate claimed drought assistance every few years.

Definitions – operational• help people identify beginning, end, & degree of severity of a drought. • specify degree of departure from average of precipitation over some time period.Usually compare current situation to historical average, often based on a 30-year period. • threshold identified usually established somewhat arbitrarily, rather than on the basis

of its precise relationship to specific impacts – e.g. beginning of a drought 75% of average precipitation over a specified time period

For agriculture compare daily precipitation values to evapotranspiration rates to determine rate of soil water depletion, then express these relationships in terms of drought effects on plant behavior (i.e., growth and yield) at various stages of crop development.

• Used in operational assessment of drought severity & impacts by tracking meteorological variables, soil water, & crop conditions during growing season, continually reevaluating potential impact of these conditions on final yield.

Also used to analyze drought frequency, severity, & duration for a given historical period. • But require weather data & impact data (e.g., crop yield), according to nature of

definition applied. • Developing a climatology of drought for a region provides a greater understanding of

its characteristics & probability of recurrence at various levels of severity. • Infor extremely beneficial in the development of response & mitigation strategies &

preparedness plans.

Definitions – Meterological Drought

usually on basis of degree of dryness (compared to “normal” or average amount) and duration of dry period.

Must be considered as region specific since atmospheric conditions that result in deficiencies of precipitation are highly variable from region to region.

• identify periods of drought on basis of number of days with precipitation less than some specified threshold.

• But only appropriate for regions characterized by a year-round precipitation regime such as a tropical rainforest, humid subtropical climate, or humid mid-latitude climate. Locations such as Manaus, Brazil; New Orleans, Louisiana (U.S.A.); & London, England.

• For areas with a seasonal rainfall pattern, such as the central USA, northeast Brazil, West Africa, and northern Australia. Extended periods without rainfall are common in Omaha, Nebraska (U.S.A.); Fortaleza, Ceará (Brazil); and Darwin, Northwest Territory (Australia),

• Above definition unrealistic in these cases. • Other definitions may relate actual precipitation departures from average

amounts on monthly, seasonal, or annual time scales.

Definitions – Agricultural DroughtLinks drought to agricultural impacts, • focusing on precipitation shortages, • differences between actual and potential evapotranspiration, • soil water deficits, • reduced ground water or reservoir levels, etcPlant water demand depends on prevailing weather conditions, biological

characteristics of the specific plant, its stage of growth, and the physical and biological properties of the soil.

Good agricultural drought definition should account for • variable susceptibility of crops during different stages of crop development,

from emergence to maturity. • deficient topsoil moisture at planting may hinder germination, leading to low

plant populations per hectare and a reduction of final yield.• But if topsoil water is sufficient for early growth requirements, deficiencies in

subsoil water at this early stage may not affect final yield if subsoil moisture is replenished as the growing season progresses or if rainfall meets plant water needs.

Definitions – Hydrological DroughtAssociated with effects of periods of precipitation (including snowfall) shortfalls on

surface or subsurface water supply (i.e. streamflow, reservoir and lake levels, ground water).

• frequency & severity often defined on a watershed or catchment or river basin scale.Hydrologists more concerned with deficiency through hydrologic system. Usually out of phase with or lag occurrence of met & agric droughts. • takes longer to show up in hydrological system such as soil water, streamflow, &

ground water & reservoir levels. • => impacts are out of phase with impacts in other economic sectors. • For example, a precipitation deficiency may result in a rapid depletion of soil water

that is almost immediately discernible to agriculturalists, but impact of this deficiency on reservoir levels may not affect hydroelectric power production or recreational uses for many months.

• Water in hydrologic storage systems (e.g., reservoirs, rivers) is often used for multiple & competing purposes (e.g., flood control, irrigation, recreation, navigation, hydropower, wildlife habitat), further complicating the sequence and quantification of impacts.

• Competition for water in these storage systems escalates during drought and conflicts between water users increase significantly.

Definitions – hydrological consequencesHydrological Drought and Land Use• Climate is a primary contributor but other factors such as changes in land use (e.g., deforestation), land

degradation, & construction of dams all affect the hydrological characteristics of the basin. • Because regions are interconnected by hydrologic systems, impact of met-drought extends beyond borders of

precipitation-deficient area. • USA example, met-drought severely affect portions of northern Rocky Mountains &northern Great Plains

region(USA). However, since Missouri River & its tributaries drain this region to south, can be significant hydrologic impacts downstream.

• Similarly, changes in land use upstream may alter hydrologic characteristics such as infiltration & runoff rates, => more variable streamflow & higher incidence of hydrol-drought downstream.

• Bangladesh example - an increased frequency of water shortages in recent years because land use changes occurred. Land use change = way human actions alter frequency of water shortage even when no change in the frequency of met- drought observed.

Sequence of Drought Impacts• impacts associated with met-, agric- & hydrological drought emphasizes differences. • When drought begins, agric sector is usually first affected due to heavy dependence on stored soil water which

is rapidly depleted during extended dry periods. • If precipitation deficiencies continue, then people dependent on other sources of water begin feel effects of

shortage. If rely on surface water (i.e., reservoirs and lakes) & subsurface water (i.e., ground water) usually last to be affected.

• A short-term drought may have little impact on these sectors, depending on hydrologic system & water use requirements.

• Sequence repeated when receive rain - recovery of surface & subsurface water supplies is delayed.• Soil water reserves are replenished first, followed by streamflow, reservoirs and lakes, and ground water. Drought impacts diminish rapidly in agric sector because of its reliance on soil water, but linger for months or even

years in other sectors dependent on stored surface or subsurface supplies. Ground water users, often last to be affected by drought during its onset, may be last to experience a return to normal water levels.

The length of recovery period is a function of intensity of drought, its duration, & precipitation received.

Definitions - Socioeconomic Drought• Associate supply & demand of some economic good affected by elements of drought. • differs because depends on time & space processes of supply & demand to identify or

classify droughts.The supply of many economic goods, such as water, forage, food grains, fish, and

hydroelectric power, depends on weather. • Due to natural variability of climate, water supply is ample in some years but unable to

meet human & environmental needs in other years. • occurs when demand for an economic good exceeds supply as a result of a weather-

related shortfall in water supply. – For example, in Uruguay in 1988–89, drought resulted in significantly reduced hydroelectric

power production because power plants were dependent on streamflow rather than storage for power generation. Reducing hydroelectric power production required the government to convert to more expensive (imported) petroleum and stringent energy conservation measures to meet the nation’s power needs.

Mostly demand for economic goods is increasing as a result of increasing population and per capita consumption. Supply may also increase because of improved production efficiency, technology, or construction of reservoirs that increase surface water storage capacity.

If both supply & demand are increasing, critical factor is relative rate of change. Is demand increasing more rapidly than supply? If so, vulnerability & incidence of drought

may increase in the future as supply and demand trends converge.

Understanding Your Risk or Impacts of Drought

direct = Reduced crop, rangeland, and forest productivity; increased fire hazard; reduced water levels; increased livestock and wildlife mortality rates; and damage to wildlife and fish habitat

indirect = consequences• eg a reduction in crop, rangeland, and forest productivity may

result in reduced income for farmers • increased prices for food and timber, unemployment, reduced

tax revenues because of reduced expenditures, increased crime, foreclosures on bank loans to farmers and businesses, migration, and disaster relief programs.

http://www.drought.unl.edu/risk/impacts.htm

Understanding Your Risk or Impacts of Drought

Direct or primary impacts are usually biophysical. • categorized as economic, environmental, or social.Can be positive impact also provide water-related services• income loss is another indicator • Environmental losses • Social impacts mainly involve public safety, health, conflicts between water

users, reduced quality of life, and inequities in the distribution of impacts and disaster relief.

Drought represents one of the most important natural triggers for malnutrition and famine,

• Economic Impacts• Environmental Impacts• Social Impacts • http://www.drought.unl.edu/risk/impacts.htm

Planning for Drought

Use Wilhite 10 step plan from USA National Drought Mitigation Center

Consider impacts on various sectorsHow & why of monitoring droughtPossible mitigation measures to put in place

Wilhite Ten Step Plan

• 1) Appointment of drought task team• 2) Purpose and objectives of drought plan• 3) Seek participation and resolve conflict• 4) Inventory / list of resources and groups• 5) Develop structure and prepare drought plan• 6) Integrate science and policy• 7) Publicize plan • 8) Implement plan• 9) Develop education programmes• 10) Post-drought evaluation

http://www.drought.unl.edu/plan/handbook/process.htm

Mitigation of drought

For who? By who? Do what?= taking action in advance of drought to reduce

long-term risk & effects or impactNeed a wide range of tools• Policies• Activities• Plans• Programmes

Mitigation of drought

Agronomic practises• Change planting dates • Change tillage & mulch practices• Change fertiliser/kraal manure applications• Intercropping• Short season cultivars or Shorter season crops• Disease & pest managementWater management• storage of runoff water in earthen dams• water harvesting• mini-in-field catchments• organic mulch between rows

Useful Websites• Donald A. Wilhite, Michael J. Hayes, & Cody L. Knutson

Drought Preparedness Planning: Building Institutional Capacityhttp://drought.unl.edu/plan/handbook/10step_rev.pdfhttp://www.drought.unl.edu/whatis/what.htm

• South African website for seasonal forecastshttp://www.gfcsa.net/csag.htmlData - Stats for RSA stationhttp://old.weathersa.co.za/Menus/MSClimData.jspSAWS seasonal forecasthttp://old.weathersa.co.za/FcastProducts/LongRange/images/PCP_SEA_SA.gif

• Australian Bureau of Meteorology – Drought– http://www.bom.gov.au/climate/drought/livedrought.shtml

• NOAA – Drought Information Center– http://www.drought.noaa.gov/– http://www.droughtoutlook.com/

• US National Drought Mitigation Center– http://drought.unl.edu/index.htm

• Glossary of definitions– http://drought.unl.edu/kids/glossary.htm

Understanding Your Risk of Drought

Economic Impacts

Costs and losses to agricultural producers

Crops• annual and perennial crop losses • Damage to crop quality • Income loss for farmers due to reduced crop

yields • Reduced productivity of cropland (wind

erosion, long-term loss of organic matter, etc.)

• Insect infestation & Plant disease • Wildlife damage to crops • Increased irrigation costs • Cost of new or supplemental water resource

development (wells, dams, pipelines)

Timber• Loss from timber production• Tree disease • Insect infestation • Impaired productivity of forest land • Direct loss of trees, especially young ones

http://www.drought.unl.edu/risk/economic.htm

Livestock• Costs and losses to livestock producers• Reduced productivity of rangeland • Reduced milk production • Forced reduction of foundation stock • Closure/limitation of public lands to grazing • High cost/unavailability of water for livestock• High cost/unavailability of feed for livestock • Increased feed transportation costs • High livestock mortality rates • Disruption of reproduction cycles (delayed

breeding, more miscarriages) • Decreased stock weights • Increased predation • Range & Wildland fires Fisheries• Loss from fishery production• Damage to fish habitat • Loss of fish and other aquatic organisms due

to decreased flows

General economic effects• Decreased land prices • Loss to industries directly dependent on agricultural production (e.g., machinery and fertilizer

manufacturers, food processors, dairies, etc.) • Unemployment from drought-related declines in production ; Rural population loss • Strain on financial institutions (foreclosures, more credit risk, capital shortfalls) • Revenue losses to federal, state, and local governments (from reduced tax base) • Reduction of economic development • Fewer agricultural producers (due to bankruptcies, new occupations) Recreation and tourism industry• Loss to manufacturers and sellers of recreational equipment • Losses related to curtailed activities: hunting and fishing, bird watching, boating, etc. Energy-related effects• Increased energy demand and reduced supply because of drought-related power curtailments • Costs to energy industry & consumers associated with substituting more expensive fuels for

hydroelectric power Water Suppliers• Revenue shortfalls and/or windfall profits • Cost of water transport or transfer • Cost of new or supplemental water resource development Transportation Industry• Loss from impaired navigability of streams, rivers, and canals • Decline in food production/disrupted food supply• Increase in food prices • Increased importation of food (higher costs)

Environmental Impactshttp://www.drought.unl.edu/risk/environment.htm

• Damage to animal species & Disease • Reduction and degradation of fish and

wildlife habitat • Lack of feed and drinking water • Greater mortality due to increased

contact with agricultural producers, as animals seek food from farms and producers are less tolerant of the intrusion

• Increased vulnerability to predation (from species concentrated near water)

• Migration and concentration (loss of wildlife in some areas and too many wildlife in other areas)

• Increased stress to endangered species • Loss of biodiversity • Hydrological effects• Lower water levels in dams, reservoirs,

lakes,

• Reduced flow from springs & streamflow• Loss of wetlands • Estuarine impacts (e.g., changes in salinity levels)

• Increased groundwater depletion, land subsidence, reduced recharge

• Water quality effects (e.g., salt concentration, increased water temperature, pH, dissolved oxygen, turbidity)

• Damage to plant communities• Loss of biodiversity • Loss of trees - urban landscapes,

shelterbelts, wild conservation areas • Increased number and severity of fires• Wind and water erosion of soils, reduced

soil quality• Air quality effects (e.g., dust, pollutants)

• Visual and landscape quality (e.g., dust, vegetative cover, etc.)

Social ImpactsHealth • Mental and physical stress (e.g., anxiety,

depression, loss of security, domestic violence)

• Health-related low-flow problems (e.g., cross-connection contamination, diminished sewage flows, increased pollutant concentrations, reduced fire fighting capability, etc.)

• Reductions in nutrition (e.g., high-cost food limitations, stress-related dietary deficiencies)

• Loss of human life (e.g., from heat stress, suicides)

• Public safety from forest and range fires • Increased respiratory ailments • Increased disease caused by wildlife

concentrations Increased conflicts -Water user & Political &

Management & Other social conflicts (e.g., scientific, media-based)

• Reduced quality of life, change lifestyle

• Increased poverty in general • Population migrations (rural to urban areas,

migrants into RSA) • Loss of aesthetic values • Reduction or modification of recreational

activities • Disruption of cultural belief systems (e.g.,

religious and scientific views of natural hazards)

• Reevaluation of social values (e.g. priorities, needs, rights)

• Public dissatisfaction with government drought response

• Perceptions of inequity in relief, possibly related to socioeconomic status, ethnicity, age, gender, seniority

• Loss of cultural sites• Increased data/information needs,

coordination of dissemination activities• Recognition of institutional restraints on

water use • http://www.drought.unl.edu/risk/social.htm

Drought Practical• Go to USA - UCAR webpage & work through • “Undertsanding Drought” module & • then complete quiz. • Be sure to fill in Catherine Odendaal’s email address (kovsiekat@gmail.com )

as your “supervisor’s email” so it can count as you practical mark for this week.

• • Go to the following webpage:• http://www.meted.ucar.edu/climate/drought/index.htm• first register as a user before you can complete the module.• listened to module, • Complete “quiz” to • Submit as practical assignment• • This must be completed by midnight on Thursday 17 March 2011.