Drought

Lake Chad has shrunk dramatically over the last four decades due to a decrease in rainfall and an increase in the amount of water used for irrigation projects. Its surface area was 25 000 sq km in the early 1960s, compared with 1350 sq km in 2001. Image acquired 19 December 2007 by the MERIS (Medium Resolution Imaging Spectrometer) instrument aboard ESA’s Envisat satellite. Image: ESA, CC BY-SA 3.0 IGO.

Definition

Drought may be considered in general terms a consequence of a reduction over an extended period of time in the amount of precipitation that is received, usually over a season or more in length. It is a temporary aberration, unlike aridity, which is a permanent feature of the climate. Seasonal aridity (i.e., a well-defined dry season) also needs to be distinguished from drought. It should be noted that drought is a normal, recurrent feature of climate, and it occurs in virtually all climatic regimes (UNDDR).

Facts and figures

Droughts are often predictable: periods of unusual dryness are normal in all weather systems. Advance warning is possible (WHO).

By 2025, 1.8 billion people will experience absolute water scarcity, and 2/3 of the world will be living under water stressed conditions (UNCCD).

Drought can be defined according to meteorological, agricultural, hydrological and socio-economic criteria.

  • Meteorological, when precipitation departs from the long-term normal
  • Agricultural, when there is insufficient soil moisture to meet the needs of a particular crop at a particular time. Agricultural drought is typically evident after meteorological drought but before a hydrological drought
  • Hydrological, when deficiencies occur in surface and subsurface water supplies
  • Socio-economic, when human activities are affected by reduced precipitation and related water availability. This form of drought associates human activities with elements of meteorological, agricultural, and hydrological drought (FAO).

Related content on the Knowledge Portal

Actualités

Screenshot of the FAO Hand-in-Hand geospatial platform.

The Food and Agriculture Organization of the United Nations (FAO) has launched a geospatial data platform that aims to help build stronger food and agriculture sectors post COVID-19. The Hand-in-Hand system provides access to a wide range of data on food, agriculture, socioeconomics and natural resources.

The platform features over one million geospatial layers and thousands of statistics series related to food security, crops, soil, land, water, climate, fisheries, livestock, forestry and more. It also includes information on COVID-19's impact on food and agriculture. A video describing the tool and its use cases is available online.

The data included in the system has been sourced from FAO and other leading public data providers across the UN and NGOs, academia, private sector... read more

Publishing date: 09/09/2020
Tropical cyclone Fani over the eastern coast of India on 2 May 2019. Image: NASA.

According to the latest issue of an annual disaster statistics report, floods were the deadliest type of disasters in 2019, followed by extreme temperature, while storms affected the highest number of people. Published by the Centre for Research on the Epidemiology of Disasters (CRED), “Natural disasters 2019 - Now is the time to not give up” draws on data recorded in the Emergency Events Database (EM-DAT), which saw the addition of 396 disasters that affected a total of 95 million and caused $103 billion in economic losses around the world. 

Accounting for 40 per cent of disaster events, Asia suffered the highest impact with 45 per cent of deaths and 74 per cent of total affected. India, which saw cyclone Fani cause destruction in 2019, was the country most affected... read more

Publishing date: 20/08/2020
Areas flooded and damaged following cyclone Idai, northwest of Beira. Image: European Union/Christian Jepsen.

In recent years, Mozambique has suffered severe floods and droughts that have impacted urban and rural communities throughout the country. In the March and April 2019, tropical cyclones Idai and Kenneth triggered major floods in Mozambique, Malawi, Zimbabwe, and Comoros.  The Port of Beira was hard hit, as cyclone Idai destroyed transmission lines and bridges, leaving the port without access to these lifelines for several days.   In contrast the powerful El Niño event of 2016 triggered major droughts that affected most of the country. Thousands of farmers lost their crops and their cattle and had to rely on humanitarian assistance to cope with the impacts of this event.

Taking into consideration the benefits of the use of satellite imagery to map the geographic extent of floods and to monitor the effects of drought on vegetation; the Federal University of Santa Maria of Brazil (UFSM), in its role as a UN-SPIDER Regional Support Office (RSO); and UN-SPIDER joined forces to... read more

Publishing date: 10/08/2020
Regional Support Offices mentioned:
Sentinel 3. Image: ESA.

A new project of the European Space Agency (ESA) aims to combine data from two different Copernicus Sentinel missions to provide estimates of evapotranspiration at the scale of a single field. The European Space Agency’s Sentinels for Evapotranspiration (Sen-ET) project brings together optical data from the Sentinel-2 mission and thermal data from the Sentinel-3 mission to produce evapotranspiration maps at a resolution of 20m. This is not only relevant for sustainable agriculture, but also for water resource management, and can help understand and respond to climate variability, predict droughts and address heatwaves.

Evapotranspiration describes the process of water being transferred from the Earth’s land and ocean surfaces to the atmosphere through evaporation and transpiration from plants. Monitoring evapotranspiration helps identify crops... read more

Publishing date: 31/07/2020
Central-pivot agricultural fields along the Orange River in South Africa. Image: contains modified Copernicus Sentinel data (2016), processed by ESA.

A grantmaking collective committed to creating and mobilizing labeled datasets that facilitate the development of machine learning applications to address urgent problems has launched a new request for proposals (RFP) for funding. Lacuna Fund, which aims to support as many organizations as possible in using artificial intelligence for social good in low- and middle-income contexts, focuses on agriculture, health and languages. This latest request for proposals will fund labeled agricultural datasets for machine learning in sub-Saharan Africa, whether referenced to Earth observation data or related to other aspects of the crop and animal agricultural system.

Interested organizations headquartered in Africa or having a substantial partnership with organization(s) headquartered in Africa can submit their applications until 3 September 2020. Further details are available... read more

Publishing date: 29/07/2020
Report cover page. Image: UNESCAP.

The United Nations Economic and Social Commission for Asia and the Pacific (ESCAP) has published a policy study concerning the impending climate risk scenarios in South Asia and their intersection with the COVID-19 pandemic. The aim of this report is to facilitate policy actions that could protect communities at risk as well as to lay the foundations of resilient recovery of the most vulnerable in South Asia. 

ESCAP has published two additional reports this year, one on the “Impact and Policy Responses for COVID-19 in Asia and the Pacific”, which presents an initial assessment of the COVID-19 pandemic in Asia and sub-regional report entitled “COVID-19 and South Asia: National Strategies and Subregional Cooperation for Accelerated Inclusive, Sustainable and Resilient Recovery”, which provides a comprehensive situation analysis of South Asia. This newly published policy study is hence an addition to the previous reports and sheds light on how to manage... read more

Publishing date: 23/07/2020
Image: UNFPA.

In the latest example of anticipatory humanitarian action, the United Nations released $5.2 million from the Central Emergency Response Fund (CERF) to help communities in Bangladesh prepare themselves ahead of major monsoon floods. The allocation of funds to agencies in the country to prepare to deliver support was triggered by a forecast from the Global Flood Awareness System (GloFAS), which predicted areas having a greater than 50 per cent chance of experiencing a severe flood between 14 and 16 July. Following a second forecast by the Government’s Flood Forecasting & Warning Centre (FFWC) on 11 July, aid workers began distributing the aid.

The swift assistance provided in Bangladesh comes as United Nations Under-Secretary-General for Humanitarian Affairs and Emergency Relief Coordinator Mark Lowcock has agreed to allocate up to $140 million from the UN... read more

Publishing date: 21/07/2020

Événement

Synthetic Aperture Radar (SAR) data can be acquired day and night, even in cloudy conditions, providing a dense time-series suitable for trend analysis and change detection.  Environmental applications for SAR data include:

  •     forest inventory, biomass estimation and condition monitoring
  •     emergency response to floods and landslides
  •     habitat and crop mapping
  •     soil moisture monitoring
  •     offshore infrastructure and vessel monitoring
  •     detection of pollution such as oil spills and illegal waste

The Joint Nature Conservation Committee (JNCC) is organising a series of online training sessions on understanding, accessing and using SAR data. The training will be delivered by Iain Woodhouse, Professor of Applied Earth Observation at the University of Edinburgh and author of Introduction to Microwave Remote Sensing.

... read more

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