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GRoW – WATER AS A GLOBAL RESOURCE
ABSTRACT
In times of drought, water resources are insufficient. These water shortages often have negative effects on agricultural produc-
tivity and on associated socioeconomic factors, causing reduced income, food shortages and even famines. The overall objective
of GlobeDrought is to develop an integrated drought risk information system which will adequately describe causal links in the
formation and development of droughts, connections between the various types of drought hazards (meteorological, hydrolo-
gical and soil moisture), and associated vulnerabilities. With its planned monitoring and experimental early warning system, the
project aims to reduce the time between satellite-based data collection, identification of a drought risk and the implementation
of potential countermeasures by political decision-makers and those involved in international humanitarian aid. The global-scale
analyses focusing on drought impacts on agricultural systems will be supplemented by detailed analyses for regions heavily
affected by droughts such as Southern Africa (South Africa and Zimbabwe), Eastern Brazil, Western India, and the Missouri River
Basin of the United States. The results of literature reviews and expert consultations show that it is very important how drought
risk analyses are conceptualized and that there is no consolidated, commonly shared framework and methodology for drought
risk assessments at the moment. GlobeDrought is therefore also going to contribute to methodological improvements and more
precise terminology in drought risk and impact assessments. First outcomes of the global and regional studies show that the
modeling tools and sensor data used in GlobeDrought provide a consistent picture of drought development across the domains
meteorology, hydrology, agronomy and economy.
GlobeDrought: A global-scale tool for characterising
droughts and quantifying their impact on water resources
GlobeDrought – towards improved drought risk
analysis and projection at global and regional scales
Stefan Siebert , Natalie Cornish, Petra Döll, Olena Dubovyk, Olga Engels, Ehsan Eyshi-Rezaei, Helena Gerdener, Javier
Gonzalez, Valerie Graw, Michael Hagenlocher, Claudia Herbert, Jürgen Kusche, Tobias Landmann, Isabel Meza, Hamideh
Nouri, Eklavyya Popat, Daniel Rupp
Full information on author affiliations can be found p. 68
Keywords: Integrated risk assessment, vulnerability, agricultural systems, water supply, drought
INTRODUCTION
Drought is considered a major determinant of variability in
crop yields and crop production worldwide. In particular
regions that are less integrated into the world market face
challenges to ensure sufficient food supply when exposed to
drought. Historically, one adaptation to aridity or frequent
drought events was the development of irrigation infrastruc-
ture to protect crops and farms against missing rainfall. The
global area equipped for irrigation increased from about 63
million hectares in year 1900 to more than 306 million hecta-
res in year 2005. It is estimated that about 90% of the global
consumptive freshwater use is for irrigation (Döll et al., 2012).
In particular during droughts irrigation water requirement is
high so that meteorological droughts caused by missing rain-
fall can translate faster into hydrological droughts charac-
terized by declining water storage in surface water bodies and
aquifers. Shortage in water supply for irrigation schemes can
then transfer a hydrological drought into a soil moisture
drought, characterized by low soil moisture and low crop
yields. It is therefore essential to monitor the drought situation
and to propose useful countermeasures when critical thresh-
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GlobeDrought
olds are surpassed. Operational early warning systems for
droughts try to address the problem. However, they are most-
ly only capable of characterizing the status quo, or offer limit-
ed forecasts for droughts in the near future – e.g. the next
three to six months. These early warning systems generally do
not sufficiently integrate variables and drought indicators. In
particular, they do not adequately describe causal links in the
formation and development of droughts, connections
between the various types of droughts (meteorological,
hydrological and soil moisture), and socioeconomic and
ecological factors as key drivers of exposure and vulnerability.
The project intends to fill this gap by developing an integrat-
ed drought risk information system, including a monitoring
and experimental early warning system. The overall objective
is to gain a better understanding of the development of
droughts and the links between different drought types,
including the role of the socio-economic setup affecting the
vulnerability and exposure to drought. Existing drought risk
analyses and impact frameworks will be evaluated and an
improved drought risk analysis framework will be implement-
ed into the new drought risk information system. The drought
information system will provide general information at global
scale and more detailed region specific information for project
regions with a distinct socio-economic setup and distinct
environmental and climatic conditions. Consequently, target
groups differ and comprise organizations with the mandate
to inform policy makers such as the Global Drought Observa-
tory (GDO) of the European Union, organizations involved in
international humanitarian aid, regional and national water
management organizations or farmers in the project regions.
METHODS
To analyze drought risks and drought impacts, an improved
drought risk analysis framework is being developed and used,
comprising of indicators for drought hazard, exposure and
vulnerability which together determine drought risk and rela-
ted impacts (Figure 1). Indicators for drought hazard, exposure
and vulnerability are specific to the impacts to be analyzed.
The drought risk information system will comprise of both, a
global component and regional components, providing more
specific analyses for the regions Southern Africa (South Africa
and Zimbabwe), Western India (Maharashtra), Eastern Brazil
(Ceará) and the Missouri River Basin in the United States. The
information system will be developed and tested using histori-
cal data for climate, satellite based water storage anomalies,
land use, crop yields, water use, trade and socio-economic indi-
cators complemented with vegetation health analyses, using
remote sensing. The experimental early warning system will
provide data, maps and tools for near real time drought moni-
toring. In addition, a projection of the development of droughts
within the next year will be provided, based on ensembles of
historical climate data as a replacement of climatic data for the
future. Probabilities will be calculated to quantify how likely it is
that a drought becomes more severe, remains similar, be-
comes less severe or disappears within the projected time
period. The drought hazard analysis will be complemented by
an indicator-based assessment of present-day vulnerabilities as
a major determinant of sectoral drought impacts.
The regional drought assessments will be adapted in a co-
design process to the requirements of partners and stake-
holders in the project regions. Therefore, the regional drought
information systems will be more precise and of higher spatial
resolution while the indicators used and the impacts studied
will vary for the specific regions. In contrast, the global infor-
mation system will facilitate comparisons of drought impacts,
drought risks and drought conditions across the globe.
To quantify drought hazard and drought impacts, a set of
hydrological and crop models will be combined with
advanced methods to generate drought related information
from remote sensing. Total water storage anomalies detected
from the gravity satellite mission GRACE are used to improve
trends in water storages simulated by the hydrological model
WaterGAP. Further, we also compute hydrological indicators
by using total water storage changes from GRACE directly.
Spatial patterns and interannual variability in sowing and
Figure 1: The conceptual framework used in the GlobeDrought project to
analyze drought risk and drought impacts at global and regional scale.
GRoW – WATER AS A GLOBAL RESOURCE
50
Figure 2: Accumulated drought months per year from 3−Month−SPEI in RSA (A), accumulated water storage deficit volume calculated with the model
WaterGAP (B), deviation of AET/PET ratio from long-term mean for maize calculated with GCWM (C) for year 2005. Drought Severity Index (Zhao et al., 2017)
for the project regions using total water storage changes from GRACE gravity measurements (D) for period 2003-2017.
harvest dates for major crops determined by MODIS satellite
data are used to inform the crop model solution SIMPLACE
<LINTUL5,SLIMWater,SLIMRoots> to improve the simulation
of drought impacts on crop productivity and irrigation water
requirement.
INTERIM RESULTS AND DISCUSSION
Indicators to be considered for drought hazard, exposure, and
vulnerability analysis and hence for characterizing the risk of
specific drought impacts, were selected based on a compre-
hensive literature review (Hagenlocher et al., submitted),
internal discussions during an indicator workshop held at the
University of Bonn on 16 Feb 2018, and expert consultations
during the first stakeholder workshop (03/04 May 2018) at
United Nations University in Bonn, Germany. The specific rele-
vance of each indicator was evaluated using an online survey
which was designed in collaboration with the Global Drought
Observatory (GDO) of the European Commission, and sent to
124 international drought experts. A set of more than 50 indi-
cators was defined and out of this indicator set specific indica-
tors are selected, depending on the drought impact to be
studied, the project region and the relevance identified by the
experts. Based on the response of the regional and global
experts it was decided that drought impacts on agricultural
systems (irrigated agriculture, rainfed agriculture, agro-pastoral
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GlobeDrought
LIST OF REFERENCES
Döll, P., Hoffmann-Dobrev, H., Portmann, F. T., Siebert, S., Eicker, A., Rodell, M., Strassberg, G.,Scanlon, B. R. (2012). Impact of water with-
drawals from groundwater and surface water on continental water storage variations. Journal of Geodynamics, 59–60, 143-156.
Eyshi Rezaei, E., & Siebert, S. (2018). Global patterns of agronomic drought risk. Mitt. Ges. Pflanzenbauwiss. 30, 45-46.
Hagenlocher, M., Meza, I., Anderson, C., Min, A., Renaud, F. G., Walz, Y., Sebesvari, Z. (submitted). Assessing drought vulnerability and risk
across spatial and temporal scales: persistent gaps and research agenda. Environmental Research Letters.
Zhao, M., Geruo, A., Velicogna, I. and Kimball, J.S. (2017). A global gridded dataset of GRACE drought severity index for 2002-14: comparison
with PDSI and SPEI and a case study of the Australia millennium drought. Journal of Hydrometeorology, 18, 2117-2129.
Contact
Coordinator: Prof Dr Stefan Siebert
University of Göttingen, Institute for Crop Sciences
Tel.: +49 551 39 24359
E-mail: stefan.siebert@uni-goettingen.de
Website: https://grow-globedrought.net/
BMBF Project ID: 02WGR1457A-F
systems) and drought impacts on water supply will be studied
at the global scale. In addition, depending on the relevance
and local user needs, more specific impacts will be studied at
the regional level. A publication, describing the novel drought
risk analysis framework and the indicators selected so far, is
under preparation.
By analysing remote sensing based indicators and the output
of the global hydrological and crop models, we found that the
different, independent data sources provide consistent infor-
mation on the development of different types of drought
(Figure 2). There is also a good agreement to survey data for
agricultural production. For example, crop production in
Zimbabwe and South Africa was extremely low in year 2005,
identified as severe drought for Southern Africa (Figure 2). The
results of the crop model applied at global scale showed that
the severity of drought impacts differs between the specific
crops, for example between crop cultivated in the winter or
summer season or those cultivated in the wet or dry season,
so that crop specific information needs to be considered in
drought impact assessments (Eyshi Rezaei & Siebert, 2018).
The GlobeDrought teams could also make considerable
progress with the coupling of models and the assimilation of
remote sensing data into hydrological and crop models. This
is of major importance for the more detailed analyses to be
performed at regional level. Results were presented so far at
four international conferences and in four journal articles.
Additional publications in journals are under preparation. The
project received considerable attention in the media, for
example it was featured in WaterSolutions (issue 03/18).
The indicator data obtained from analyses at global scale are
currently being categorized and implemented into the
web-based drought information system hosted by Remote
Sensing Solutions. Metadata descriptions have already been
collected, the data itself are now being structured according
to the conceptual framework shown in Figure 1.
CONCLUSIONS & OUTLOOK
The results of the global drought risk analysis and first regional
results are promising. The indicator data are now being trans-
ferred to the web-based information system to be presented
and discussed at the second stakeholder workshop of the
project which will take place in autumn 2019.