Europe 1901-2000 : Tx, Tn précipitations

[charles.muller]

Une analyse 1901-2000 des Tn, Tx et précipitations extrêmes sur l'Europe (Ouest > 60E)

- Augmentation de 1°C des T en hiver, 0,8°C en été

- Augmentation plus soutenue des Tx que des Tn pour l'hiver (mais larges différences régionales)

- Augmentation plus soutenue des Tx que des Tn pour l'été en Europe centrale seulement

- Hausse de 12% des précipitations en hiver

- Pas de hausse des fortes précipitations (90, 95, 98 percentiles)

- Pas de tendance des précipitations en été

- Légère tendance non significative (mais régionale) à des précipitations plus intenses mais moins fréquentes en été

- Les auteurs soulignent que les données restent hétérogènes, avec des zones mal couvertes historiquement

Le point que je retiens est que ni la sécheresse ni les pluies extrêmes ne sont globalement au rendez-vous pour 1901-2000, malgré un réchauffement plus important que le reste du globe (hors Arctique). Mais le pessimisme n'est pas interdit pour 2001-2100

**

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, D22106, doi:10.1029/2006JD007103, 2006

Indices for daily temperature and precipitation extremes in Europe analyzed for the period 1901–2000

Anders Moberg (et une vingtaine d'auteurs)

Abstract - We analyze century-long daily temperature and precipitation records for stations in Europe west of 60°E. A set of climatic indices derived from the daily series, mainly focusing on extremes, is defined. Linear trends in these indices are assessed over the period 1901–2000. Average trends, for 75 stations mostly representing Europe west of 20°E, show a warming for all temperature indices. Winter has, on average, warmed more (∼1.0°C/100 yr) than summer (∼0.8°C), both for daily maximum (TX) and minimum (TN) temperatures. Overall, the warming of TX in winter was stronger in the warm tail than in the cold tail (1.6 and 1.5°C for 98th and 95th, but ∼1.0°C for 2nd, 5th and 10th percentiles). There are, however, large regional differences in temperature trend patterns. For summer, there is a tendency for stronger warming, both for TX and TN, in the warm than in the cold tail only in parts of central Europe. Winter precipitation totals, averaged over 121 European stations north of 40°N, have increased significantly by ∼12% per 100 years. Trends in 90th, 95th and 98th percentiles of daily winter precipitation have been similar. No overall long-term trend occurred in summer precipitation totals, but there is an overall weak (statistically insignificant and regionally dependent) tendency for summer precipitation to have become slightly more intense but less common. Data inhomogeneities and relative sparseness of station density in many parts of Europe preclude more robust conclusions. It is of importance that new methods are developed for homogenizing daily data.

[Invité]

Le point que je retiens est que ni la sécheresse ni les pluies extrêmes ne sont globalement au rendez-vous pour 1901-2000, malgré un réchauffement plus important que le reste du globe (hors Arctique).

pourtant si je lis ceci:

0,8°C en été

et ceci:

Pas de tendance des précipitations en été

cela veut bien dire qu'en été il fait plus chaud et qu'il ne pleut pas plus.

C'est bien une tendance à la sécheresse en été.

nota

si on regarde les données NOAA cette fois pour l'Europe de l'ouest entre 10W et 20E et 35-60N, de 1976 à 2005, on a:

Tm annuelle:+0.46°C/décennie

Tm JJA:+0.63°C/décennie

Tm DJF:+0.29°C/décennie

avec globalement une augmentation annuelle des précipitations sur la période de 0.52mm/décennie, ce qui est très modéré.

Une augmentation de température de 1.4°C sur la période entraîne une augmentation de l'évaporation de pas loin de 10%, non-compensée par une augmentation des précipitations < à 1%.

Il y a donc diminution du taux d'humidité des sols.

Si j'en crois ces données bien entendu. /emoticons/wink@2x.png 2x" width="20" height="20">

PS: pour les 10% je suis loin d'être sûr.

[charles.muller]

Tu as raison sur la sécheresse, quoiqu'il faut sans doute la définir plus précisément en termes météo (un épisode de sécheresse au sens propre ou une tendance à la sécheresse). Disons que plus de chaleur à précipitation égale, cela augmente sans doute ce risque de sécheresse, même si les précipitations peuvent être assez réparties pour qu'il n'y ait jamais une période de X semaines sans pluie.

Sinon, je parlais du XXe siècle, pas des 30 dernières années. Je pense cependant que si 1975-2000 avait changé la tendance, on le repérerait dans les analyses 1901-2000.

Si tu vas sur le bilan GIEC du XXe siècle, cela concorde plutôt avec l'analyse de Moberg et al. :

http://www.grida.no/climate/ipcc_tar/wg1/077.htm

Précipitations :

"Over the 20th century, annual zonally averaged precipitation increased by between 7 to 12% for the zones 30°N to 85°N and by about 2% between 0°S to 55°S (Figure 2.25(ii)). The increase in the Northern Hemisphere is likely to be slightly biased because adjustments have not been made for the increasing fraction of precipitation falling in liquid as opposed to frozen form. The exact rate of precipitation increase depends on the method of calculating the changes, but the bias is expected to be small because the amount of annual precipitation affected by this trend is generally only about a few per cent. Nevertheless, this unsteady, but highly statistically significant trend toward more precipitation in many of these regions is continuing. For example, in 1998 the Northern Hemisphere high latitudes (55°N and higher) had their wettest year on record and the mid-latitudes have had precipitation totals exceeding the 1961 to 1990 mean every year since 1995."

(...)

Humidité des sols en Eurasie :

"Soil moisture data for large regions of Eurasia (Robock et al., 2000) show large upward trends. The rate of increase is more than 1 cm/decade in the available soil moisture in the top 1 m of soil. These large positive trends occur simultaneously with positive trends in temperature that would normally reduce soil moisture. Increases in precipitation (and cloud cover, Section 2.5.5) are believed to have more than compensated for the increased losses due to evapotranspiration."

(...)

***

Sur la période récente, il y a le papier de Dai 2006 dans le J Clim sur l'humidité relative (RH) et l'humidité spécifique à la surface (q). Les deux sont en hausse significative sur l'Eurasie entre 1975 et 2005, mis pas de données précises sur l'Europe.

Il me semblait que j'avais vu un papier sur l'humidité des sols spécifiquement, mais je ne le retrouve plus.

Journal of Climate

Article: pp. 3589–3606 | Full Text | PDF (3.71M)

Recent Climatology, Variability, and Trends in Global Surface Humidity

Aiguo Dai11. National Center for Atmospheric Research,* Boulder, Colorado

ABSTRACT

In situ observations of surface air and dewpoint temperatures and air pressure from over 15 000 weather stations and from ships are used to calculate surface specific (q) and relative (RH) humidity over the globe (60°S–75°N) from December 1975 to spring 2005. Seasonal and interannual variations and linear trends are analyzed in relation to observed surface temperature (T) changes and simulated changes by a coupled climate model [namely the Parallel Climate Model (PCM)] with realistic forcing. It is found that spatial patterns of long-term mean q are largely controlled by climatological surface temperature, with the largest q of 17–19 g kg−1 in the Tropics and large seasonal variations over northern mid- and high-latitude land. Surface RH has relatively small spatial and interannual variations, with a mean value of 75%–80% over most oceans in all seasons and 70%–80% over most land areas except for deserts and high terrain, where RH is 30%–60%. Nighttime mean RH is 2%–15% higher than daytime RH over most land areas because of large diurnal temperature variations. The leading EOFs in both q and RH depict long-term trends, while the second EOF of q is related to the El Niño–Southern Oscillation (ENSO). During 1976–2004, global changes in surface RH are small (within 0.6% for absolute values), although decreasing trends of −0.11% ∼ −0.22% decade−1 for global oceans are statistically significant. Large RH increases (0.5%–2.0% decade−1) occurred over the central and eastern United States, India, and western China, resulting from large q increases coupled with moderate warming and increases in low clouds over these regions during 1976–2004. Statistically very significant increasing trends are found in global and Northern Hemispheric q and T. From 1976 to 2004, annual q (T) increased by 0.06 g kg−1 (0.16°C) decade−1 globally and 0.08 g kg−1 (0.20°C) decade−1 in the Northern Hemisphere, while the Southern Hemispheric q trend is positive but statistically insignificant. Over land, the q and T trends are larger at night than during the day. The largest percentage increases in surface q (∼1.5% to 6.0% decade−1) occurred over Eurasia where large warming (∼0.2° to 0.7°C decade−1) was observed. The q and T trends are found in all seasons over much of Eurasia (largest in boreal winter) and the Atlantic Ocean. Significant correlation between annual q and T is found over most oceans (r = 0.6–0.9) and most of Eurasia (r = 0.4–0.8), whereas it is insignificant over subtropical land areas. RH–T correlation is weak over most of the globe but is negative over many arid areas. The q–T anomaly relationship is approximately linear so that surface q over the globe, global land, and ocean increases by ∼4.9%, 4.3%, and 5.7% per 1°C warming, respectively, values that are close to those suggested by the Clausius–Clapeyron equation with a constant RH. The recent q and T trends and the q–T relationship are broadly captured by the PCM; however, the model overestimates volcanic cooling and the trends in the Southern Hemisphere.