Lena M. Tallaksen
Drought under Climate Change
SoCoCA final workshop, 19-20 March 2013, Oslo
Global pressure on water
• Demographics and increasing
consumption are the most important drivers
or pressure on water
• Agriculture is the largest consumer of
freshwater by far – about 70% of all
freshwater withdrawals go to irrigated
agriculture
• About 20% of water used globally is from
groundwater, and this share is rising rapidly,
particularly in dry regions
• Water scarcity may limit food production
and supply, putting pressure on food prices
• Water availability is lower during drought
• Climate change is expected to make the
situation worse.
The 2011-12 drought in the US
The US drought is
a global problem
According to the UN, food prices
jumped 6% in July, whereas corn
prices surged nearly 23%,
following the severe deterioration
of maize crop prospects in the US
(9 Aug. 2012).
Drought under Climate Change
Outline
• What is drought?
– drought definition
– drought propagation
– drought indices
• Drought and water resources
– current climate
– future projections
• Concluding remarks
Photo: Scott Olson / Getty Images
What is Drought?
Deviation from normal conditions:
• occurrence of below average natural water
availability
• occurs in all hydroclimatological regions
• sustained and regionally extensive
• creeping disaster
• different types of drought (meteorological,
soil water, groundwater, streamflow)
Do not confuse with:
• aridity
• water scarcity
Water resources – global distribution
Gudmundsson et al., 2011
Drought impacts
• Economic losses from climate-related disasters have increased
due to increasing exposure
• Economic losses are higher in developed countries
• Fatalities are higher in developing countries
• Drought is a complex phenomenon that must be described in
terms of several variables to assess the wide ranging impacts
on environment, economy and society.
The 2003 drought in Europe
• More than 100 million people
affected (a third of the EU territory)
• Heat wave in Southern Europe
(~30.000)
• Total cost at least € 8.7 billion
(forest fires, crop loss)
• Navigation problems on large rivers
• Lowest water level in Danube in
160 years and the Rhine v/Lobith
• Death of fish (almost 300C)
• Closure of power plants
• Damage of buildings due to
subsidence
Drought on the European agenda!
Drought propagation
Meteorological
Situation
Natural climate variability
Persisting anticyclonic
pressure systems
Less / no
precipitation
Meteorological
Drought
Agricultural
Drought
Precipitation
deficiency
High temperature, low
humidity, greater
sunshine, etc.
Increased evaporation and
transpiration
Soil water deficiency
Plant water stress,
reduced biomass
and yield
Reduced recharge
Hydrological
Drought
Streamflow
deficiency
Depletion of groundwater
reservoirs
Tallaksen & van Lanen, 2004
Droughts are regional events
and recent severe droughts pose questions like:
•
•
•
•
•
In a global context, what are the main
impacts of drought on the economy,
society and environment?
Is drought a growing problem?
What is the forecast trend for drought
frequency/severity?
Which regions will be hardest hit?
What can be done to alleviate drought
risk?
Drought covers large spatial and temporal
scales, and thus requires transnational
data for its analysis
How to index drought - SPI
How to index drought - PDSI
How to index drought - classes
Does Not Replace Local Information
U.S. Drought Monitor
Climatological Drought Indices
Drought Indices (normalised for direct comparison):
SPI – transform accumulated precipitation to std normal
• recommended by WMO, different time lags (1, 3, 6,12 month)
SPEI – transform climatic water balance (P-PET) to std normal
• Relatively new, a more complete estimate of available water
EU project on Drought (DROUGHT-R&SPI) :
• Drought indices will be link to climate predictors, impacts, etc.
• Choice of distribution for the pan-European scale (SPI, SPEI)
• SPEI relies on choice of PET algorithm
 Requires rigorous testing
Global change
Two main approaches to assess the impact of global
(climate and human impacts) change on freshwater
resources:
i)
Analysis of observed data for changes
and trends
i)
Climate projections using physicallybased models
The latter requires that the models being used have been
evaluated for the current climate.
Climate change - observations
Warming of the climate system in recent decades is evident
from observations
• Hot days, hot nights and heat waves have become more
frequent in the last 50 years
• Precipitation over land has generally increased in high northern
latitudes and decreased in the subtropics (10-30oC) since
1970s
• Globally a decrease in streamflow is seen in parts of West
Africa, Southern Europe and southern parts of South America
(but, overall increase).
IPCC Fourth
Assessment Report
Climate change - projections
IPCC Technical Paper on Water (2008)
• Global warming is projected to be in the range 1.8 – 4.0oC
and mean precipitation will increase (5% over land)
• Heat waves will continue to become more frequent
• Precipitation decrease in some subtropical and lower
mid-latitude regions (particular in summer);
• Annual river runoff will decrease over some dry regions at
mid-latitudes and in the dry tropics and increase at high
latitudes and eastern temperate latitudes;
• Seasonality will continue to change, particular in cold
climates
• more severe hydrological extremes is expected as a a
a result of an intensifying of the hydrological cycle;
• Little is know on groundwater
Modelled observed changes in runoff – Projected
Trends 1963 – 2000
Stahl et al. (2012)
1971-2000 versus 2071-2100
Gudmundsson et al. (2011)
Gudmundsson et al., 2011
Change in variability, CV (annual)
Gudmundsson et al., 2011
Hydrological droughts (runoff)
Model performance (eight large-scale models): weekly
persistence in drought area for the European domain
Tallaksen & Stahl, submitted
Hydrological droughts
Model performance and variability
The best performing models also have the
highest persistence. This can likely be
related to the conceptualization of
hydrological processes, in particular water
storage and release, in the models.
The choice of model influences the estimated drought
characteristics, and care should be taken when
analysing the output from only one or a limited number
of models.
Tallaksen & Stahl, submitted
Climate change
Observed changes – Drought (PDSI)
Palmer Drought Severity Index
Dai, 2011
PDSI – sensitivity to EPOT
Temp. based
Pen-Mon
Sheffield et al., 2012
Drought drivers
Seneviratne, 2012
Future climate
Hot-spot: Mediterranean region
Changes in Standardized Precipitation Index (SPI12) and Soil
Moisture Anomalies (SMA) as projected by CMIP5 Models
Orlowsky and Seneviratne, 2013
EDC Website – www.geo.uio.no/edc
Drought Reference Database
• Continuous (SPI, SPEI,
Runoff) and event based
drought statistics (indicators)
• Linked to Impact Database
• Goal is to implement a
dynamic site structure
(PHP/SQL) to better handle
updates
Concluding remarks
Drought is likely to become a larger threat to
mankind as:
– climate change scenarios predict more frequent and
extreme droughts in regions that are already dry
– there is an increasing pressure on water resources
Drought is a natural hazard that cannot be prevented,
but knowledge and good management practice can
assist in minimizing the impact of drought
Drought forecasts combined with improved water
management are needed.
Thank you for your attention!
SoCoCA final workshop, 19-20 March 2013, Oslo
References
Dai, A. (2011) Drought under global warming: a review. Advanced review, 2, 45-65, John Wiley
& Sons, Ltd.
Dai, A. (2013) Increasing drought under global warming in observations and models. Nature
Climate Change 3, 52-58.
Gudmundsson, L., Tallaksen, L.M. & Stahl, K. (2011) Projected changes in future runoff
variability - a multi model analysis using The a2 emission scenario. WATCH Technical
Report 49 (www.eu-watch.org).
Orlowsky, B. & Seneviratne, S.I. (2012) Elusive drought: uncertainty in observed trends and
short- and long-term CMIP5 projections. Hydrol. Earth Syst. Sci. Discuss., 9, 13773–13803.
Seneviratne, S.I (2012) Historical drought trends revisited. Nature 49, 338-339.
Sheffield, J., Wood, E.F. and Roderick, M.L. (2012) Little change in global drought over the past
60 years. Nature 491, 435-438.
Stahl, K., Tallaksen, L.M., Hannaford, J. & van Lanen, H.A.J. (2012) Filling the white space on
maps of European runoff trends: estimates from a multi-model ensemble. Hydrol. Earth
Syst. Sci. Discuss., 9, 2005–2032.
Tallaksen, L.M. & van Lanen, H.A.J. (2004) (Eds) Hydrological Drought – Processes and
Estimation Methods for Streamflow and Groundwater. Developments in Water Sciences
48. Elsevier B.V., the Netherlands, 580p.
Tallaksen, L.M., Stahl, K. : High model variability in reproducing large-scale hydrological
droughts in Europe. ERL (submitted March 2013).