Soil Moisture Drought in Europe: A Compound Event of Precipitation and Potential Evapotranspiration on Multiple Time Scales

Abstract

Compound events are extreme impacts that depend on multiple variables that need not be extreme themselves. In this study, we analyze soil moisture drought as a compound event of precipitation and potential evapotranspiration (PET) on multiple time scales related to both meteorological drought and heat waves in wet, transitional, and dry climates in Europe during summer. Drought indices that incorporate PET to account for the effect of temperature on drought conditions are sensitive to global warming. However, as evapotranspiration (ET) is moisture limited in dry climates, the use of such drought indices has often been criticized. We therefore assess the relevance of the contributions of both precipitation and PET to the estimation of soil moisture drought. Applying a statistical model based on pair copula constructions to data from FluxNet sites in Europe, we find at all sites that precipitation exerts the main control over soil moisture drought. At wet sites PET is additionally required to explain the onset, severity, and persistence of drought events over different time scales. At dry sites, where ET is moisture limited in summer, PET does not improve the estimation of soil moisture. In dry climates, increases in drought severity measured by indices incorporating PET may therefore not indicate further drying of soil but the increased availability of energy that can contribute to other environmental hazards such as heat waves and wildfires. We therefore highlight that drought indices including PET should be interpreted within the context of the climate and season in which they are applied in order to maximize their value.

Impact of precipitation and increasing temperatures on drought in eastern Africa

“…Simple correlations between monthly precipitation, temperature, PET, and soil moisture (not shown) support the conclusions of Manning et al (2018) on the influence of precipitation and PET on soil moisture at dry sites. They found that at waterlimited sites the influence of precipitation on soil moisture is much larger than the influence of temperature, via PET, on soil 20 moisture.…”

Increased probability of compound long-duration dry and hot events in Europe during summer (1950–2013)

“…The results may also have implications for the persistence of soil moisture drought conditions. High amounts of precipitation are required for recovery from large moisture deficits induced by intense drying , Manning et al 2018 while general increases in evaporation can push environments towards a climatically drier state (Samaniego et al 2018).…”

“…The joint occurrence of extremely long-duration and high magnitude events may thus lead to higher soil moisture deficits than events where only one characteristic is extreme. Larger deficits can produce longer lasting soil moisture droughts as higher amounts of precipitation are then required for drought recovery , Manning et al 2018.…”

Unraveling the influence of atmospheric evaporative demand on drought and its response to climate change

“…The indirect effects are more important given that under unlimited soil water content more AED usually means more plant transpiration. These hydrological effects are usually complex since they depend on the runoff generation processes and the length of the dry period, but more ET will generally reduce soil moisture (Manning et al, ; Teuling et al, ). This AED effect could propagate throughout other parts of the hydrological cycle and cause a streamflow reduction (Vicente‐Serrano, Azorin‐Molina, Sanchez‐Lorenzo, Revuelto, López‐Moreno, et al, ; Vicente‐Serrano, Azorin‐Molina, Sanchez‐Lorenzo, Revuelto, Morán‐Tejeda, et al, ; Vicente‐Serrano, Lopez‐Moreno, et al, ).…”