Projected changes in droughts and extreme droughts in Great Britain strongly influenced by the choice of drought index

Abstract

Abstract. Droughts cause enormous ecological, economical and societal damage, and are already undergoing changes due to anthropogenic climate change. Understanding, anticipating and communicating these changes is essential to a wide range of stakeholders. In this study, the projected impacts of climate change on future atmospheric droughts in Great Britain were assessed for two warming levels (2 °C and 4 °C above pre-industrial levels) using the UKCP18 regional climate projections. As projected changes can be very sensitive to the choice of drought index, two indices were compared: the Standardized Precipitation Index (SPI), and the Standardized Precipitation Evapotranspiration Index (SPEI, which unlike the SPI, accounts for increasing potential evapotranspiration). The SPI and SPEI were used to quantify drought frequency, extent and duration of all droughts and of only extreme droughts. To provide context, aridity and seasonal precipitation and potential evapotranspiration changes were also assessed, as well as seasonal contributions to dryness at a yearly time scale. The UKCP18 regional simulations project (strongly) increasing drought frequency and extent due to climate change based on the SP(E)I almost everywhere in Great Britain. Importantly, the relative increase in frequency and extent is much more pronounced for extreme droughts than for more moderate droughts. Increasing longer-term dry conditions can be attributed mostly to more frequent dry and extremely dry summers, for which normal to wet winters are decreasingly able to compensate (even where winters are projected to become wetter). In general, using the SPEI results in far greater increases in drought frequency and extent than using the SPI. These differences are so substantive that at +2 °C the SPEI6-based projected changes reach a similar magnitude to the SPI6-based changes at +4 °C. Finally, projected changes in the distribution of drought durations depend on the drought index, region and warming level. These results illustrate that the choice of atmospheric drought index can have a decisive influence on changes in projected drought characteristics, and therefore users of these indices should be aware of the importance of potential evapotranspiration in their intended context when choosing a drought index. The stark differences between SPI- and SPEI-based projections highlight the need to understand the interplay between increasing atmospheric evaporative demand and moisture availability under a changing climate.

Propagation and Characteristics of Hydrometeorological Drought Under Changing Climate in Irish Catchments

“…For instance, SPI is widely applied and can detect drought conditions at different timescales, ranging from monthly to multi‐annual (Mckee et al., 1993). However, SPI is based on precipitation alone and fails to consider the role of temperature on drought events and frequencies (Reyniers et al., 2022) and may not be suitable for drought projections and changes under climate change (Vicente‐Serrano, et al., 2020a). Similarly, for hydrological drought, Standardized Streamflow Index (SSI) only considers streamflow, whereas water managers may be interested in other hydrological components such as groundwater that may be critical in understanding the development and duration of drought events (Wossenyeleh et al., 2021).…”

Assessment of Artificial Neural Network through Drought Indices

“…The UK has suffered clusters of drought in the form of long and short drought series [79,80]. The following conclusions were drawn with the recent study carried out for the UK indicating projected changes in droughts using SPEI and SPI: increase in drought risk with increasing global mean surface temperature, drought frequency seasonality, duration greatly varies spatially, increase in English regions and Wales, decreases in North and West Scotland, and a large difference between SPI and SPEI was observed [81]. SPEI-6 was the best predictor of drought impacts on agriculture in UK regions compared to the reported drought impacts, however, the findings indicate that the relationship varies spatially between the large heterogeneous regions and needs smaller spatial units [82].…”

Propagation from Meteorological Drought to Hydrological Drought Using SPI and SPEI Combined with the Adapted Threshold Level Method

“…Therefore, there is a growing advocacy for the adoption of the SPEI over SPI, as the former includes the evapotranspiration component influenced by rising temperatures (Reyniers et al, 2022;Tomasella et al, 2022;Vicente-Serrano et al, 2022).…”