MaRIUS has investigated the following aspects of droughts, related to the human and environmental domains:

What are droughts?

Droughts are natural events which occur when a period of low rainfall creates a shortage of water. Each drought is different, with the nature, timing and impacts varying according to location and which sectors are affected such as public water supply, agriculture, the environment or industry. Water scarcity describes the relationship between water demand and availability.

Drought events can also be defined based on the duration of the rainfall deficit and the particular impacts that evolve over time. The Environment Agency identify three main types of drought which may occur separately or together:

  • An Environmental Drought happens as a result of a shortage of rainfall which has a detrimental impact on the environment. For example, reduced river flows, exceptionally low groundwater levels and insufficient moisture within soils.
  • An Agricultural Drought occurs when there isn’t enough rainfall and moisture in soils to support crop production or farming practices such as spray irrigation.
  • A Water Supply Drought is an exceptional  shortage of rainfall causes water companies concern about supplies for their customers.

Identifying drought events

Drought indices can incorporate various climate and hydrological data within a single indicator that can be used for analysing trends and relaying information to stakeholders, policy makers and the public in a clear format. The drought index value is often presented as a single number, which can be far easier to understand and use than raw data. In MaRIUS we used the Standardized Precipitation Evapotranspiration Index (SPEI) to determine drought. The SPEI reflects changes in rainfall as well temperature on water demand through the inclusion of potential evapotranspiration (PET).

The SPEI can be calculated for different time periods so that the dynamics of different types of drought (environmental, agricultural, or water supply drought) can be assessed. Drought onset, severity, and duration are categorised based on the SPEI values, with negative values below a set threshold used to determine drought.


There has been a number of droughts in England over the past 40 years. The most recent notable droughts were 1975-1976, 1989-1992, 1995-1996, 2004-2006 and 2010-2012. Over-abstraction to meet the needs of growing populations, agricultural and industrial use, and the effects of climate change are causing multiple challenges in many water-stressed regions, and these are likely to increase in the future.


However, a study of historical events alone does not provide sufficiently diverse and extreme conditions to study the full range of possible drought conditions and impacts that may occur in the future. As such, MaRIUS has developed an extensive ‘drought event set’ covering the past, present day and future drought conditions.

The event set has been used to provide a range of possible weather time series and assess projected changes in drought characteristics for different time-periods that:

  • could have occurred in the past (‘Baseline’, 1900-2006)
  • might occur in the near future (‘Near Future’, 2020-2049)
  • might occur in the far future (‘Far Future’, 2070-2099)