CLIMA EN ESPAÑA: PASADO, PRESENTE Y FUTURO Contribución a un Informe de Evaluación del Cambio Climático Regional Febrero 2009 Presentación: Salat & Pascual

Posible efecto de la diferencia de calentamiento entre el mar y el aire a las precipitaciones en la cuenca mediterránea Possible effect of air-sea differential warming trends on the Mediterranean basin precipitation seasonality Jordi SALAT y Josep PASCUAL Institut de Ciències del Mar de Barcelona (CSIC) P. Marítim, E Barcelona. ¿VOLVERÁN LAS LLUVIAS DE PRIMAVERA?

¿Planeta Tierra? Vista centrada sobre 4°S 154°W

¿Where is the water? Oceans: km 3 Continents: km 3 Atmosphere:0, km 3 Global water cycle On land: Rivers, lakes, etc:0, km 3 Continental ice: km 3 Groundwater:5, km 3

Water exchanges (hm 3 /s)? -3,512,2Atmosphere 2,2-1,3Continent 13,5--Ocean AtmosphereContinentOceanFrom↓ To→ Percents on global water cycle: Precipitation on land:3,5/15,7=22% Rivers:1,3/15,7= 8% Global water cycle

Turnover times: Continental* water:35/0,069 ≈ 500 a Marine water:1350/0,041 ≈ a(66x) Precipitation on land from evaporation on continents:2,2 hm 3 /s=0, km 3 /a (63%) ocean:1,3 hm 3 /s=0, km 3 /a (37%) *including permanent ice caps and ground water Global water cycle

37 % of precipitation on the continents is originated in the ocean through evaporation Global water cycle

However, Most research programs on the Global Water Cycle do not properly treat the ocean’s role. Small components of the terrestrial water cycle receive great attention, yet elements of the much larger oceanic water cycle are ignored! So that, We know rather little about oceanic freshwater fluxes because Water Cycle research has focused on land and atmospheric processes, and neglected the much larger oceanic component.

Evaporation over the ocean On what depends? 1.Sea surface temperature must be higher than air temperature and 2. Evaporation will +Increase with sea sea surface temperature +Increase with wind —Decrease with relative humidity of the air Recall: 37 % of precipitation on the continents is originated in the ocean through evaporation

If the Earth is retaining heat, warming the air is faster than the ocean. Because: Specific heat of the ocean is 1100 times higher than the atmosphere. Thus: 1. Air may allow more water vapour 2. Evaporation may increase 3. Water cycle is accelerating Global warming But… The ocean retains heat for longer

As warming the air is going faster than the ocean, the occurrence of sea surface warmer than the air will be less frequent. Hence: Evaporation over the ocean will decrease and Precipitation on the continent originated from the sea could decrease. Global warming This is the point! As warming the air is going faster than the ocean, the occurrence of sea surface warmer than the air will be less frequent. Hence: Evaporation over the ocean will decrease and Precipitation on the continent originated from the sea could decrease.

The Mediterranan View centered on 55°N 0°

The Mediterranean The Mediterranean isn’t the sea between the lands … but the sea between mountains

Dry south Dominant cold & dry northerly winds The Mediterranean

Surrounded by mountains Small river basins* Part of the southern side is very dry (desertic) Frequent strong and dry winds in northern side Evaporation exceeds precipitation over the basin 1.It imports sea water from the ocean, and 2. exports fresh water to other basins *excluding the Nile river and Black sea basins The Mediterranean

Water balance Net export of water out of the basin through the atmosphere:1, km 3 /a (must equal net input)

The Mediterranean Is a big desalination plant producing ~ 5500 m 3 /s for the neighbours That’s solidarity! But... may this change with “Global Warming” ?

Local scale: Observations since 1974 at L’Estartit

air Sea surface Sea at 80 m Monthly temperature series

Summary of trends °C/a AnnualWinterSpringSummerFall Air Temp. 0,0540,0450,0820,0620,053 Sea surface Temp. 0,0360,020 0,011 min. 0,043 0,060 max. 0,034 0,049 max. 0,034 0,025 min. Sea 80 m 0,0230,0160,0190,0150,040 Mean Temp (0-80 m) 0,0320,0190,0320,040 Air Temp. - SST 0,0310,0240,0530,0240,021

Annual Cycle

Annual cycle

“Summer period” length

Annual cycle

Air and sea surface temperature series (April-May)

“Dry period” length

Summary of trends

Trends in local precipitation

Conclusions 1.A warming trend has been observed in the air and in all the sampled levels at sea (0-80 m) 2.The maximum trend has been observed in spring 3.Warming trend is higher in the air than at sea 4.The sea stratified period (summer) has been extended for 49 days in 34 years (24 days anticipated) 5.The period with air warmer than sea surface has been extended for 75 days in 35 years (41 days anticipated) 6.This evolution is unfavourable to evaporation during spring. 7.These changes may cause a reduction of spring rainfall, which accounted for ~30% of the total annual in the Mediterranean basin. 8.The marine component of the Water Cycle is quite relevant but still not well understood.

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