ROBUST ASSESSMENT OF THE EXPANSION AND RETREAT OF MEDITERRANEAN CLIMATE IN THE 21 st CENTURY.

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1 ROBUST ASSESSMENT OF THE EXPANSION AND RETREAT OF MEDITERRANEAN CLIMATE IN THE 21 st CENTURY. Andrea Alessandri, Matteo De Felice, Ning Zeng, Annarita Mariotti, Yutong Pan, Annalisa Cherchi, June-Yi Lee, Bin Wang, Kyung-Ja Ha, Paolo Ruti, and Vincenzo Artale Supplementary material Figure S1. Spatial distribution of Mediterranean (light green), other Warm Temperate (dark green), Snow (cyan) and Arid climates (olive green) following the Köppen-Geiger classification for the historical period. The climate type of each grid point was identified by applying the method to monthly-mean surface air temperature from ERA- Interim reanalysis and from CMAP precipitation dataset. The map in this figure was drawn using Matlab. 1

2 2 ROBUST EXPANSION AND RETREAT OF MEDITERRANEAN CLIMATE IN THE 21 ST CENTURY (a) Conditional observed frequency CMIP5 probability (b) Figure S2. (a) Probability of Mediterranean climate simulated by the CMIP5 models for the historical period (green). For each model the Mediterranean grid points are identified following the Köppen-Geiger classification. Then, for each grid point the ensemble average of the models is computed by using equal weights. The observed historical ( ) mediterranean climate presence/absence is shown as well (red). When green and red colors overlap (becoming brown), there is correspondence between observation and CMIP5. Only CMIP5 probabilities exceeding 0.5 can overlap with observations. (b) Reliability diagram for the dichotomous [1, 0] event of presence/absence of MED climate. The x-axis represents the modeled probability and the y-axis the observed conditional frequency. The y = x dashed line indicate theoretical perfect reliability. All land grid points are used in the computation. The map in this figure was drawn using Matlab.

3 ROBUST EXPANSION AND RETREAT OF MEDITERRANEAN CLIMATE IN THE 21 st CENTURY 3 Figure S3. JJA moisture budget analysis over Euro-Mediterranean region for (a) precipitation change at the end of 21 st century with respect to historical ( minus ) period. The contribution from (b) thermodynamic term, (c) dynamical term and (d) evaporation are reported. See text for explanation. The maps in this figure were drawn using Grid Analysis and Display System. Figures S3-S6 show the decomposition of the projected precipitation change ( minus ) for Euro-med (Figs. S3 and S4) and WNA (Figs. S5 and S6) and during both the winter (Figs. S4 and S6) and summer (Figs. S3 and S5) seasons. In order to decompose the precipitation change (P ) into its thermodynamic, dynamical and evaporation change (E ) components, the vertically integrated moisture budget is done in terms of the precipitation departures from the period, following the analysis published by [1, 2]: (1) P = ω p q + E + P dyn where prime represents the difference from the reference historical period, and the overbar denotes the climatology in the reference. The angle brackets stand for vertically integrated quantities through the troposphere. E is the evaporation and q is the specific humidity (in W/m 2 by absorbing the latent heat per unit mass L). The first term on the right-hand side of equation 1 corresponds to the thermodynamic precipitation change [1], which represents the direct moisture effect (i.e. the increase of moisture transport by assuming no change in atmospheric circulation). The third term corresponds to a dynamic precipitation change,

4 4 ROBUST EXPANSION AND RETREAT OF MEDITERRANEAN CLIMATE IN THE 21 ST CENTURY Figure S4. Same as Figure S3 but for the winter season. The maps in this figure were drawn using Grid Analysis and Display System. computed here as the residual term in 1 and contains the contribution of all the linear and non-linear atmospheric dynamics components [1].

5 ROBUST EXPANSION AND RETREAT OF MEDITERRANEAN CLIMATE IN THE 21 st CENTURY 5 Figure S5. Same as Figure S3 but for the western North America region. The maps in this figure were drawn using Grid Analysis and Display System. Figure S6. Same as Figure S5 but for the winter season. The maps in this figure were drawn using Grid Analysis and Display System.

6 6 ROBUST EXPANSION AND RETREAT OF MEDITERRANEAN CLIMATE IN THE 21 ST CENTURY Figure S vs difference of the ensemble-mean coldest winter month temperature (T min). Dashed lines represent the 3 C T min level for (red) and for (black). The map in this figure was drawn using Matlab.

7 ROBUST EXPANSION AND RETREAT OF MEDITERRANEAN CLIMATE IN THE 21 st CENTURY 7 Figure S8. (a) Spatial pattern of the wintertime (December-January-February) leading combined EOF (C-EOF) of 30-year running-mean precipitation (mm/d; shaded), sea level pressure (SLP; Pa; contours) and 850hPa vector wind (m/s). Scale for the vector wind is shown. (b) Standardized first combined principal component (C-PC1; red), Siberian High Index (SHI, average SLP over E, 45-70N; green) and Arctic Oscillation index (AO, leading principal component of the wintertime SLP computed poleward of 20 N; blue). C-PC1 and AO signs were reversed to compare with SLP drop over siberian high. SHI and AO were also computed on 30-years running-mean data. The map in this figure was drawn using Grid Analysis and Display System.

8 8 ROBUST EXPANSION AND RETREAT OF MEDITERRANEAN CLIMATE IN THE 21 ST CENTURY (a) (b) (c) Figure S9. Projected vs probability change of the Mediterranean climate over (a) South America, (b) South Africa and (c) Australia. Dashed line is the 0.5 contour for P MED during the reference period and the markers indicate the transitions from warm temperate to Mediterranean (Warm Temp. to MED; crosses), Mediterranean to arid (MED to ARID; circles) and snow to Mediterranean (SNOW to MED; triangles) climates. Symbols in bold indicate that at least 95% of the models that change climate type agree in the transition. Only the probability changes that passed a Monte Carlo significance test at the 5% level are shaded. The maps in this figure were drawn using Matlab.

9 ROBUST EXPANSION AND RETREAT OF MEDITERRANEAN CLIMATE IN THE 21 st CENTURY 9 References [1] Chou C., Neelin J.D., Chen C-A., Tu J-Y., 2009: Evaluating the rich-get-richer mechanism in tropical precipitation change under global warming. J Climate, 22, [2] Cherchi A., A. Alessandri, S. Masina, and A. Navarra, 2010: Effects of increased CO2 levels on monsoon circulations. Clim. Dyn., 37(1-2), , doi: /s