Precipitation response to extreme soil moisture conditions over the Mediterranean

Abstract

The intimate link between soil moisture and precipitation makes it a “chicken-and-egg situation” that challenges climate studies of the continental water cycle. This association is particularly acute over the Mediterranean, increasingly exposed to droughts with climate change. This study aims at deciphering the impact of spring soil moisture state in the Mediterranean on subsequent warm season precipitation. In an idealized setup, two distinct climate models are used to generate extreme dry or wet soil conditions, and run climate simulations initialized and/or forced by these conditions. Changes in precipitation distribution and persistence are analyzed and where applicable compared to composites from a reanalysis. Spring soil moisture anomalies are found to be very persistent, but the precipitation response is largely model dependent. Overall, dry soils lead to a reduction of precipitation for early summer months and conversely for wet soils although with a fainter and less robust signal. On the other hand, wet soils tend to favor the persistence of precipitation throughout summer over several sub-regions. Our results highlight the stringent need to reduce the wide array of uncertainties associated to soil moisture, land-atmosphere coupling and convection in climate models, before ascertaining that soil moisture initialization could provide more skillful sub-seasonal to seasonal precipitation prediction.

Summer temperature response to extreme soil water conditions in the Mediterranean transitional climate regime

“…Most of these experiments are also described and used in the Ardilouze et al (2020) companion study, which analyzes the precipitation response to soil water extreme conditions. The large perturbation for initialization of the dry and wet experiments was necessary to reach very low water content in the soil, close to the wilting point (SXP-DI) and field capacity (SXP-WI) by the beginning of the summer.…”

“…7c, d) become remarkable after the end of the summer: while in the coupled SXPs Tmax90 is indistinguishable from EXP-B0, in the prescribed runs the difference between Tmax90 DP and Tmax90 B0 increases in September-October. The impact on Tmax and Tmax90 is further reinforced by an increase in sensible heat flux, due to a marked precipitation reduction (Ardilouze et al 2020).…”

Spatiotemporal and cross-scale interactions in hydroclimate variability: a case-study in France

“…The differences between regions are both dependent on the local expression of the climate forcing and watershed characteristics. Because those physical processes are interacting, studying cross-scale interactions in precipitation brings more insight on the dynamics behind the spectral characteristics of each region (Boé, 2013;Materia et al, 2021;Bellucci et al, 2015;Ardilouze et al, 2020).…”

“…6a), which in contradiction with recent literature. For instance, in the Mediterranean region, Ardilouze et al (2020) found no negative soil moisture precipitation feedback for interannual scales; however, the authors used two climate models to simulate soil moisture sensitivity to precipitation forcing and note that this variability is much larger in century-long reanalysis, such as NOAA's 20CR. For other regions, interannual negative soil moisture feedback was found by Boé (2013), while Sejas et al (2014) found negative ocean-land temperature differences in precipitation feedback.…”

“…In addition, all studies mentioned above either isolated particular timescales of variability or averaged the variability across timescales (e.g., global wavelet spectra), which is equivalent to a linearization of the system (Hubert et al, 1989). These studies thus ignore potential feedback mechanisms, e.g., between soil moisture, precipitation, and temperature (Materia et al, 2021;Ardilouze et al, 2020;Bellucci et al, 2015). In the presence of feedback mechanisms, interactions occur over different timescales, which are also called cross-scale interactions (Christophe Bouton, 2017).…”