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Meteorological, hydrological Meteorological, hydrological

and drought indicatorsand drought indicators

Clia Gouveia

Instituto Dom Luiz, Faculdade Cincias Universidade de Lisboa, Portugal


Drought Complexity

Drought impacts

Drought Assessment Vegetation Indices

Drought indicators: PDSI

Drought indicators: SPI

Drought indicators: SPEI

Drought Severity and Warming

Dryness and shrubland degradation

20-05-2014 2

Drought Complexity

Drought is challenging to identify over space and time

Quantification of droughts include intensity, magnitude, duration and surface extent. This quantification is an hard job!

There is no a variable that we can use to measure drought droughts are identified by means of impacts

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Drought Impacts

Drought is the most damaging meteorological hazard affecting large areas.

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Drought Impacts

Drought mortality is concentrated in developing countries, while absolute economic losses are largest in developed regions

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Drought Impacts

Droughts also cause several environmental impacts: forest decline, forest fires, soil degradation, wetland degradation, desertification

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Drought impacts: Mediterranean area

Climatic droughts are frequent in Iberian Peninsula, as well as in all the Mediterranean region, as a consequence of the large temporal variability of precipitation.

The strong dependence of vegetation dynamics on water availability has been for long recognized in the Mediterranean regions.

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Drought Impacts

However, unlike other natural disasters, such as earthquakes, droughts can be predictable, usually developing over several years.

This makes it more easy to respond to droughts as they occur.

Thus, assessing and monitoring droughts become of crucial importance.

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Drought Assessment

Traditional methods of drought assessment and monitoring rely on rainfall data as recorded in meteorological and hydrological networks.

The role of remote sensing in drought monitoring has been reinforced in recent years due to the availability of reliable satellite imagery covering wide regions over long periods.

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Vegetation Indices

NDVI was successfully tested (e.g., in regions characterized by Mediterranean climates) to monitor vegetation dynamics




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Vegetation Indices

NDVI was successfully tested (e.g., in regions characterized by Mediterranean climates) to monitor vegetation dynamics



Gouveia et al. (2008)Gouveia et al. (2008)GIMMS NDVI from 1982GIMMS NDVI from 1982--20022002


Monthly time-series of NDVI (19992006) for different land cover types


During 2004/2005, the Iberian Peninsula was hit by one of the two worst drought episodes in the last 60 years.

Vegetation Indices

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Monthly means of NDVI (1999-2006) from September to August

Vegetation Indices

Gouveia et al. (2009)Gouveia et al. (2009)

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NDVI anomalies from September to August of the year 2004/2005.

Vegetation Indices

Gouveia et al. (2009)Gouveia et al. (2009)

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Drought persistence was evaluated by adding up (for each pixel) the number of months with corrected NDVI anomalies lower than a specific threshold (-0.025).

Vegetation Indices

Gouveia et al. (2009)Gouveia et al. (2009)20-05-2014 15

Monthly time-series (19992009) averaged over Iberian Peninsula for all pixels (black), for pixels of non-irrigated arable land (red) and for pixels of needle-leaved forest (green).

Vegetation Indices

Gouveia et al. (2012)Gouveia et al. (2012)20-05-2014 16

Number of months from September 2004 to July 2005 with NDVI anomaly < -0.025

65% of Iberia in vegetative stress and low water availability conditions during spring and early summer

Drought Indices

A large number of indices have been developed to assess intensity, frequency, duration and surface extent of droughts, using different meteorological variables

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Drought Indices

The most famous drought index is the Palmer Drought Index (PDSI).

However this index presents several limitations: Strong dependence of the index with the calibration

period. To avoid these problems the calibration period should be higher than 50 years.

Many parameters of PDSI are obtained empirically for the USA region. This situations limits the applications to other regions.


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Drought Indices

Well et al. (2004) have developed the self calibrated PDSI (scPDSI). The calibration of the modified index is made based on the original dataset, improving its performance.

Maps of the monthly self-calibrating Palmer drought severity index (scPDSI) have been calculated for the period 19012002 for United States (2050N; 13060W) and Europe (3570N; 10W60E) with a spatial resolution of 0.50.5(

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Drought Indices


Mean annual scPDSI absolute trends, using CRU (Climatic Research Unit) high-resolution (0.5 lat0.5 long) dataset for the 19012002 period.

Sousa et al., 2010 Sousa et al., 2010 (Natural Hazards and (Natural Hazards and Earth System Sciences)Earth System Sciences)


Drought IndicesDrought intensity and duration

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From May to August 2012 almost all the country ( 50% in extreme drought and 20% in severe drought) was in drought. October 2012 was normal. From November 2012 to April 2013 the main territory is slightly wet, being March the wettest month with 60% of the mainland moderately wet.

Source: IPMASource: IPMA

Drought IndicesDrought intensity and duration

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From June to September 2013 a large percentage of the territory was in drought. October 2013 was a little wet but from November 2013 was dry again. From December 2013 to April 2014 the situation of dry weather was decreasing

Source: IPMA Source: IPMA 2013


Drought Indices

However the different systems responds to water scarcity with different temporal scales.

Flexible indicators to quantify the drought impacts given the different response times of hydrological, agricultural, economic systems to drought are needed .

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Drought Indices

The Standardised Precipitation Index (SPI), based on precipitation data, permit the analysis of the drought at different temporal scales.

SPI is very adjustable index, extremely useful for drought monitoring and assessing impacts.

Heim (2002). Bulletin of the American Meteorological Society.Heim (2002). Bulletin of the American Meteorological Society.

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Drought Indices

Time series of the 6 month Standardized Precipitation Index (SPI) averaged over Namibia (top) and Melbourne, Australia (bottom) between 1980-2012.

Hao et al. (2014). Hao et al. (2014). doi:10.1038/sdata.2014.1doi:10.1038/sdata.2014.120-05-2014 25

Drought Indices

SPI at Boulder, Colorado (USA) from 1894-2010 for 3, 6, 12, 24, 36 and 48 months. The original data were from (Climate Data Guide; D. Shea)

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Drought Indices

SPI for 1 month (top) and 6 months (bottom) over Iberia for 2001(left) and 2005(right)

Colorbar: blue=dry;


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20012001 20052005

Drought Indices

However, SPI is only based on precipitation and doesnt take in account variables such as temperature or evapotranspiration.

What will happen if the temperature increase significantly?

What will happen in the case of extreme events, such as heat waves?

What will happen in the case of the possible scenarios of increase temperature?

VicenteVicente--Serrano et al., 2010Serrano et al., 201020-05-2014 28

Drought Indices

Vicente-Serrano et al. (2010) have developed a new multi-scale index, the Standardized Precipitation and Evapotranspiration Index (SPEI)

SPEI uses as input precipitation and temperature

VicenteVicente--Serrano et al., 2010Serrano et al., 2010

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Drought Indices

The 3-, 12- ,18- and 24-month SPEI at Lisbon, Portugal, 19012012.

The main drought episodes occurred in the decades of 1920-30 (prolonged

drought), 1940, 1980, and 2000.

The year 2005 is extremely striking, reaching most of cases very low SPEI (

Drought Indices

Drought Severity and Duration

Number of drought

months for Lisbon,


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Drought Indices

Temperature and Evapotranspiration for the IP for March 2005 from CRU TS3.21

The 3- and 12- SPEI at IP

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Drought Indices


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Example of drought evolution on different time scales as assessed by the SPEI. The serie


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