Multi-model assessment of the impact of soil moisture initialization on mid-latitude summer predictability

Abstract

Land surface initial conditions have been recognized as a potential source of predictability in sub-seasonal to seasonal forecast systems, at least for near-surface air temperature prediction over the mid-latitude continents. Yet, few studies have systematically explored such an influence over a sufficient hindcast period and in a multi-model framework to produce a robust quantitative assessment. Here, a dedicated set of twin experiments has been carried out with boreal summer retrospective forecasts over the 1992–2010 period performed by five different global coupled ocean–atmosphere models. The impact of a realistic versus climatological soil moisture initialization is assessed in two regions with high potential previously identified as hotspots of land–atmosphere coupling, namely the North American Great Plains and South-Eastern Europe. Over the latter region, temperature predictions show a significant improvement, especially over the Balkans. Forecast systems better simulate the warmest summers if they follow pronounced dry initial anomalies. It is hypothesized that models manage to capture a positive feedback between high temperature and low soil moisture content prone to dominate over other processes during the warmest summers in this region. Over the Great Plains, however, improving the soil moisture initialization does not lead to any robust gain of forecast quality for near-surface temperature. It is suggested that models biases prevent the forecast systems from making the most of the improved initial conditions. © 2017 Springer-Verlag Berlin Heidelber

The synergy between drought and extremely hot summers in the Mediterranean

“…Despite the very different nature of this SM database, it is worth noting that the identified hot spots bewteen the NHN and NHD and the ERA-Interim/Land SM dataset agree well with the previous results for NHD/NHN in the Balkans and Iberia in May, June and July. The NHD results are also in accordance with model-based studies investigating the role of SM initial conditions on temperature predictability (Prodhomme et al 2016, Ardilouze et al 2017 which identifies the Balkans hotspot for forecasts initialized in May and valid for June-July. However, those studies did not find any clear signal over Iberia, as our results suggest.…”

“…These results are of high importance for climate modelers (Ardilouze et al 2017) and responsible authorities, as the occurrence of drought induced extreme temperatures, in particular heatwaves, can have costly impacts (Díaz et al 2006Sánchez-Benítez et al 2017. The hotspots in the BKS and northern Italy were previously identified and analyzed for SM-temperature feedbacks (Whan et al 2015, Ardilouze et al 2017.…”

“…June July consecutive months (figures 1-3) allows to identify that there is a spatial consistency on certain areas where consecutive months' present significant correlation values. This allows for the identification of hotspots of predictability of extreme hot temperatures and heatwaves in summer which are preceeded by drought conditions in the spring or early summer (figure 5) which is of highly importance for seasonal forecasting (Ardilouze et al 2017). In the case of NHD, it is possible to identify four major hotspots, namely the IP, northern Italy, northern Africa and the BKS.…”

Ocean and atmosphere influence on the 2015 European heatwave

“…Studies have shown that land surface properties such as soil moisture also influence heatwaves (e.g. Quesada et al 2012, Ardilouze et al 2017), and may therefore provide an important source of predictability for heatwaves. However, since our experiments require a coupled high-resolution prediction model, we decided to focus all our available computational resources on ocean, sea-ice and atmosphere initialisation only.…”

Declining U.S. regional and continental trends in intra‐annual and interannual extreme temperature swings

“…Having identified these characteristics of extreme temperature transitions, future research is necessary to determine the relationship between transitions and the ambient circulation features. For instance, understanding whether similar circulation features result in transitions in different regions of the country or during different times is necessary to ascribe a mechanism to the observed changes in extreme temperature variation and potentially explain the geographic patterns of change, which may be related large scale factors such as preferred wave patterns or local features such as regional soil moisture trends (e.g., Ardilouze et al, 2017).…”