EC Conference: Land as a Resource Narrative for the Presentation: Land-use changes and their impact on extreme events by Millán Millán

Transcription

1 EC Conference: Land as a Resource Narrative for the Presentation: Land-use changes and their impact on extreme events by Millán Millán Most of the contents come from the Paper in press: Extreme hydrometeorological events and climate change predictions in Europe. J. Hydrol. (2014), /j.hydrol Slide #1 Slide #2 Slide #3 Slide #4 Slide #5 Europe in spring (May?). This is intended to illustrate the brown and green parts of Europe. World s Main Catchment Basins. It shows that most of Europe is straddled over two main basins, one Atlantic and the other Mediterranean. It also illustrates the real extent of the Mediterranean Catchment Basin to Central- Eastern Europe and Africa. Detail of the Continental Water Divide over Europe, and the first two messages. First, Europe has two (very) different hydrological cycles. On the Atlantic side, up to 100% of precipitation is of Atlantic origin (IR, UK), and land-use effects on precipitation increase towards the Continental Water Divide (to 80% direct, 20% recycled). On the Mediterranean side, up to 100% of precipitation is from water recycled within the same basin, and land use is the key factor determining the amount of recycling, and precipitation. Example of precipitation component disaggregation (Millán et al. 2005a; b) in the Valencia Region of Spain, which extends from the coast to the European Continental-Water Divide (EC-WD) inland. The message is that 80% of the total precipitation in the area shown is from water recycled from the Mediterranean Basin itself. The precipitation components and percentages change towards the centre of the Mediterranean Catchment Basin. Thus in Greece and Turkey, the Atlantic component is negligible, and nearly 100% of precipitation is Mediterranean recycled water (storms or Med. cyclogenesis). A confusing issue here is that the upper atmospheric perturbations that drive the precipitation do come from the upper latitudes (eg. the North Atlantic), and they also bring a carrier component of water vapour. However, after crossing the EC-WD, that amount is not sufficient to condense readily below 2000 m. Thus, a trigger component, evapo-transpirated from the basin itself, is required to condense and precipitate. Finally, the amount precipitated is of the order (or less than) the trigger amount contributed from within the basin itself. The European Continental-water Divide, again to illustrate a point in the next Slide. Slide #6 Back trajectories for the August 11-13, 2002 flood event (Ulbrich et al. 2003) Together with the previous Slide, it illustrates that this event took place near the European Continental Divide with water vapour coming from the Western Mediterranean Basin. Trajectories of this type were compiled by van Bebber in 1891, but at that time it was difficult to explain how the Mediterranean, with

2 an average temperature of ºC at the end of summer, could evaporate so much water. We will present how this can occur. Slide #7 Possible ends of the Combined up-slope and seabreeze, henceforth the Combined breeze (CB), around the Western Mediterranean Basin (WMB). The first point is that: these circulations become self-organised over all the coasts surrounding the WMB during the day, almost every day, in summer. This self-organisation confines their vertical development and, per unit width along the coast, it limits the volumes of air involved. Land-use along the path of the CB determines whether the airmass reaches its condensation level at an altitude comparable to the mountain ridges. If it does, precipitation can occur. If it does not, the surface airmass becomes injected directly into shallow return flows aloft and forms layers over the sea. Land-use perturbations, e.g., increased heating or lower evapo-transpiration, caused by deforestation and soil sealing, build up (accumulate) along the path of the CB. This is important in more than one way, since the effects of possible solutions, e.g., afforestation to compensate the other wrongs, will also accumulate within a defined watershed. The third concept is the idea of a carrier component for the water vapour coming from the sea ( 14 g/kg), and a trigger component, provided by evapo-transpiration along the path of the CB. This latter component ( 7 g/kg) is required to compensate the heating of the airmass and keep the condensation level below the height of injection into the return flows aloft. Finally, the fourth point is the recycling of water. The most water a moist airmass can yield in the form of precipitation is about one third of the moisture it contains. Thus, in this example, the air in the CB requires a mixing ratio of 21 g/kg to reach condensation below 2000 m, and the most it can return is 1/3, i.e., 7 g/kg - which happens to be the same amount evaporated along the CB path, required to trigger the precipitation. Therefore, under the best conditions the water precipitated at the headwaters is about the same as the additional amount collected along the CB path, and the water becomes recycled within this circulatory system. These concepts could be combined to restore the summerstorm part of the hydrological system in Mediterranean landscapes. Slide #8 Fully developed storm at the end of the combined breeze on July 27, Open-type circulation. Mountain reference at centre. Slide #9 Fully developed storm at the end of the combined breeze on July 04, Open-type circulation. Mountain reference at centre. Slide #10 Slide #11 Slide #12 Aborted storm at the end of the combined breeze, Late development because of insufficient moisture. Open-type circulation. Mountain reference at centre. Closed-type circulation. The airmass in the combined breeze directly follows the return flows aloft due to insufficient moisture to trigger moist convection. Same mountain reference at left. At present, and most times, there is not enough water vapour to condense and, thus, to visualise the returning flows. Resulting accumulation of layers (water vapour and pollutants) over the Mediterranean Sea, observed at about sunset. As a reference, the mountain to the left is 798 m high.

3 Slide #13 Slide #14 Slide #15 Slide #16 Slide #17 Slide #18 Slide #19 First feedback loop relating local storm development to the temperaturemoisture balance in the combined breeze. When the loop closes, and there are no storms, the result is: (1) increasing drought inland, which further reinforces the precipitation (storm) loss loop, and (2) the formation of the Accumulation Mode (AM) of water vapour over the WMB. MODIS-Terra monthly average of the water vapour Accumulation Mode over the Mediterranean for July The day Product shows the water vapour in the combined breezes around the WMB, as introduced in Slide 5, or Slide 6. MODIS-Terra monthly average of the water vapour accumulation mode over the Mediterranean for July The Day+Night Product shows approximately (i.e., 5/6) of the total water vapour accumulated over the WMB by the end of the diurnal cycle. The monthly average equals the accumulated water vapour column after 3-to-4 days of a vertical recirculation-accumulation period. Same as Slide 11 for July 2005, Day product. Same as Slide 12 for July 2005, Day+Night product. Accumulation Mode facts. UPPER PART: Selected areas for the satellite measurements of water vapour over the Mediterranean Basin, using the Day+Night Product. The areas are overlaid on the average surface pressure for July over Southern Europe. It shows the WMB under the influence of the Azores Anticyclone, which favours the development of meso-scale vertical recirculations. The Eastern Mediterranean Basin (EMB) is under the influence of the Asian (monsoon) Low which drives strong Aetesian winds over the Agean Sea, inhibiting the development of meso-scale recirculations. LOWER PART. Accumulation mode yearly evolution over the WMB and EMB, from averaged day-by-day values for the years It shows the differences resulting from the prevailing meteorological conditions over each basin, above. The AM reaches an intense peak over the WMB during summer. Over the EMB there are two weaker accumulation modes in spring and autumn. Thus, these basins operate differently regarding their hydrological cycles. Feedback Loops. Four concatenated effects can derive from the ACCUMULATION MODE. The first derives from the greenhouse heating of water vapour (some 47 times stronger than CO 2 ) and photo-oxidants (for example O 3 is some 200x stronger than CO 2 ). Thus, when they accumulate in layers over the sea, their combined greenhouse effect overheats the WMB during the summer (response time 3 to 4 months). Peak temperatures in the warmest large water pools appear to have increased from around 26º - 27ºC at the time of WW II, to more than 35ºC recently (end of August). Slide #20 Example: average monthly accumulated water vapour for August Slide #21 Sea Surface Temperatures (SST) in the WMB for four different days in August It shows that the SST is not uniform over the basin, but rather it

4 includes large warm water pools that move from one day to the next within the basin. In the last graph the SST in the large pools are lower. Why? Slide #22 Slide #23 Slide #24 Feedback loops. The warm water pools can lead to autumn torrential rains over the islands, and/or over the coastal areas of the WMB. Lake effect. When cold air is advected over warmer water it picks up moisture that can participate in precipitation downwind. The amount of moisture recharged, and the intensity of the resulting precipitation, depend on the airwater temperature contrast and the size of the warm pool. The example is from the Stamberger Sea near Munich. Continuation of the lake effect showing the water vapour plume emerging from the warm water. It is intended to show that intense precipitation can occur downwind of the warm water but not to the sides, and illustrates how localised this type of precipitation can be (Millán et al. 1995). The evaporation of the water also cools the surface water and produces overturning of colder deeper water. This is the answer for the last graph in slide 21. Slide #25 Back trajectories for the intense precipitation event of September 5-7, 1989, and the SST for August 28 th (the last day with an unclouded satellite view). They show that the water recharge took place over warm water pools in the Tyrrenian Sea off the coast of Italy. Slide #26 Slide #27 Slide #28 Left, precipitation pattern for the September 5-7 intense precipitation event; the values at the focus were 550 L/m 2. Bottom right, simulated precipitation for that event using a modified RAMS meso-scale model and the actual SST measured several days earlier. The predicted maximum is 450 L/m 2, and the focus is displaced inland (Pastor et al. 2001). The point here is that these events can be forecasted reasonably well if the proper procedures are used. Current meteorological models, however, lack the resolution and the SST incorporation algorithms to be that specific. Final of the second feedback loop to desertification, and beginning of the third feedback loop towards continental scale effects, both resulting from the Accumulation Mode of water vapour over the WMB. LEFT. Monthly average of the accumulated water vapour over the Mediterranean and back trajectories for the August 11-13, 2002 event. This is the second effect of the Accumulation Mode. It explains the source of the water vapour in answer to van Bebber s queries in 1891, and Prof. Ulbrich s in The Mediterranean Sea does not evaporate as much water as the Gulf of Mexico (yet!), but it can accumulate evaporated water for several consecutive days before the (accumulated) water vapour becomes incorporated into a V b track event. And then, there is plenty of water vapour available. RIGHT. Water vapour trajectories from the V b event. The time delay between the onset of an accumulation mode, the water vapour buildup, and the precipitations in Central and/or Eastern Europe, i.e., if the airmass ends up going that way, is of the order of 10 days (Gangoiti et al 2011a; b).

5 Slide #29 Slide #30 Slide #31 The third effect of the Accumulation Mode is as follows: if the water vapour that should have precipitated in the WMB goes away and/or precipitates elsewhere, it increases the salinity of the WMB, and intensifies the Atlantic- Mediterranean Salinity valve at Gibraltar. Colder and lighter Atlantic water incomes to the Mediterranean at the surface, while warm and very salty water exits the Mediterranean towards the Atlantic (at some 300 m deep). Figure from an article in Nature including the Gibraltar Salinity Valve as one of the world s climate tipping points (Kemp, 2005). The outflow of very warm and very salty water at a depth of 150 m to 300 m, runs at this depth along the Portuguese seaboard and outflows somewhere from Brittany to the British Isles and seems to interfere with the Gulf Stream, the path of the Atlantic Depressions and thus, with weather in Atlantic Europe. Full feedback loops including postulated effects on the Atlantic side of the European Continental Divide (EC, 2007). Recapitulation about the propagation of land- use changes to Extreme Events at both sides of the European Continental-water Divide. The response times are as follows: The loss of storms can occur within days, e.g., results from a large forest fire (> Ha). Intense precipitations over Central Europe can occur within a week (+) after a vertical recirculatory Accumulation Period and the incorporation of the accumulated water vapour into a V b track. Mediterranean Cyclogenesis events in coastal areas and islands require a higher SST, after 2-to-4 months of increased greenhouse heating by the accumulated components. The fourth effect of the Accumulation Mode is the sulphatation and nitrification of Saharan dust involved in hurricanes in the SE-USA, and can take about one-totwo weeks (Gangoiti et al., 2001). In this case, the water vapour (and atmospheric pollutants) can travel along the Southern Atlas corridor towards the Central Atlantic (Millán et al., 1997; EC, 2001). Finally, the response of the salinity valve and its effects on the Atlantic Frontal Systems may take years, but this is not really known. Slides #32 and #33 Summary-conclusions. Slide #34 Thanks, and End. References, other than the paper above. European Commission, 2001: "A global Strategy for European atmospheric interdisciplinary research in the European research area (AIRES in ERA). Air Pollution Research Report No 76. Luxembourg: Office for Official Publications of the European Communities, 58 pp. European Commission, 2007: International Workshop on Climate Change Impacts on the Water Cycle, Resources and Quality. Report EUR Luxembourg: Office for Official Publications of the European Communities ISBN X. Gangoiti, G., L. Alonso, M. Navazo, J. A. García, M. M. Millán, 2006: North African soil dust and European pollution transport mechanisms to America during the warm season: Hidden links shown by a passive tracer simulation. J. Geophys. Res. 111, D10109, doi: /205jd

6 Gangoiti, G., E. Sáez de Cámara, L. Alonso, M. Navazo, N. Gómez, J. Iza, J. A. García, J.L. Ilardia and M. M. Millán, 2011: Origin of the water vapour responsible for the European extreme rainfalls of August 2002: 1. High-resolution simulations and tracking of airmasses. J. Geophys. Res., 116, D21102, doi: /2010JD pp. Gangoiti, G., I. Gómez-Domenech, E. Sáez de Cámara, L. Alonso, M. Navazo, N. Gómez, J. Iza, J. A. García, J.L. Ilardia, M. M. Millán, 2011: Origin of the water vapour responsible for the European extreme rainfalls of August 2002: 2. A new methodology to evaluate evaporative moisture sources, applied to the August central European rainfall episode. J. Geophys. Res., 116, D21103, doi: /2010JD pp. Kemp, M., 2005: (H. J. Schellnhuber's map of global "tipping points" in climate change), Inventing an icon, Nature, 437, Millán M., M.J. Estrela, V. Caselles, 1995; Torrential precipitations on the Spanish East coast: The role of the Mediterranean sea surface temperature. Atmospheric Research, 36, Millán M.M., R. Salvador, E. Mantilla, G. Kallos, 1997; Photo-oxidant dynamics in the Western Mediterranean in Summer: Results from European Research Projects. J. Geophys. Res., 102, D7, Millán, M. M., Mª. J. Estrela, M. J. Sanz, E. Mantilla, M. Martín, F. Pastor, R. Salvador, R. Vallejo, L. Alonso, G. Gangoiti, J.L. Ilardia, M. Navazo, A. Albizuri, B. Artiñano, P. Ciccioli, G. Kallos, R.A. Carvalho, D. Andrés, A. Hoff, J. Werhahn, G. Seufert, B, Versino, 2005: Climatic Feedbacks and Desertification: The Mediterranean model. J. Climate, 18 (5), Millán, M. M., Mª. J. Estrela, J. Miró, 2005: Rainfall Components: Variability and Spatial Distribution in a Mediterranean Area. J. Climate, 18 (14), Pastor, F., Mª. J. Estrela, D. Peñarrocha, M.M. Millán, 2001: Torrential Rains on the Spanish Mediterranean Coast: Modelling the Effects of the Sea Surface Temperature. J. Appl. Meteor., 40, Ulbrich, U., T. Brücher, A. H. Fink, G. C. Leckebusch, A. Krüger and G. Pinto, 2003: The central European floods of August 2002: Part 2 - Synoptic causes and considerations with respect to cimatic change. Weather, 58,