Precipitation response to extreme soil moisture conditions over the Mediterranean

Constantin Ardilouze,Chloé Prodhomme,Lauriane Batté,Stefano Materia,Marianna Benassi

doi:10.1007/s00382-020-05519-5

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.

Highlights

Despite large uncertainties across the globe, the Mediterranean area is one of the few where climate projections consistently foresee an increased frequency of soil moisture and precipitation droughts (Orlowsky and Seneviratne 2013)
Realism of initialized simulations Despite the idealized protocol, we attempt to assess the realism of the simulations initialized with wet or dry soil conditions by means of a composite analysis based on the Mediterranean spring soil moisture state in a century reanalysis
This composite analysis is built from the 110-year long reanalysis ERA-20C, for which years are sorted according to the value of a soil moisture index defined over the MED domain

Summary

Introduction

Despite large uncertainties across the globe, the Mediterranean area is one of the few where climate projections consistently foresee an increased frequency of soil moisture and precipitation droughts (Orlowsky and Seneviratne 2013). The impact of soil-moisture on precipitation is mostly local (Wei and Dirmeyer 2012), the sign and intensity of the feedback can be found contradictory between studies based on different evaluation methods. Local atmospheric convection and precipitation is enhanced (e.g. Schär et al 1999; Koster et al 2006) This positive feedback due to moisture recycling can compete with a negative feedback associated to boundary layer dynamics and mesoscale circulation prone to favor precipitation over dry (Taylor et al 2012) and heterogeneous soils (Guillod et al 2015). The study from Tuttle and Salvucci (2016) reveals an opposite feedback sign between the West of the United States, where increased (decreased) soil moisture favors increased (decreased) precipitation, and the East where the land precipitation feedback is negative. The contribution of soil water content to precipitation anomalies is difficult to evaluate because it is entangled with other ’non-land’ contributions such as remote sea surface temperature anomalies (Orth and Seneviratne 2017) and atmospheric dynamics (Tuttle and Salvucci 2017)

Objectives

Methods

Results

Conclusion