Hydrology and Earth System Sciences Discussions www.hydrol-earth-syst-sci-discuss.net 1812-2108 1812-2116 6 5 2009 10.5194/hessd-6-6455-2009 http://www.hydrol-earth-syst-sci-discuss.net/6/6455/2009/ http://www.hydrol-earth-syst-sci-discuss.net/6/6455/2009/hessd-6-6455-2009.html http://www.hydrol-earth-syst-sci-discuss.net/6/6455/2009/hessd-6-6455-2009.pdf 6455 6501 2009-10-22 Multilevel and multiscale drought reanalysis over France with the Safran-Isba-Modcou hydrometeorological suite J.-P. Vidal E. Martin L. Franchistéguy F. Habets J.-M. Soubeyroux M. Blanchard M. Baillon CNRM/GAME, Météo-France and CNRS, 42 avenue Coriolis 31057 Toulouse Cedex 1, France Météo-France, Direction de la Climatologie, 42 avenue Coriolis 31057 Toulouse Cedex 1, France UMR-SISYPHE, Mines-Paristech, Centre de géosciences, équipe SHR, 35 rue St honoré 77305 Fontainebleau, France Physically-based droughts can be defined as a water deficit in at least one component of the land surface hydrological cycle. The reliance of different activity domains (water supply, irrigation, hydropower, etc.) on specific components of this cycle requires drought monitoring to be based on indices related to meteorological, agricultural, and hydrological droughts. This paper describes a high-resolution retrospective analysis of such droughts in France over the last fifty years, based on the Safran-Isba-Modcou (SIM) hydrometeorological suite. The high-resolution 1958–2008 Safran atmospheric reanalysis was used to force the Isba land surface scheme and the hydrogeological model Modcou. Meteorological droughts are characterized with the Standardized Precipitation Index (SPI) at time scales varying from 1 to 24 months. Similar standardizing methods were applied to soil moisture and streamflow for identifying multiscale agricultural droughts – through the Standardized Soil Wetness Index (SSWI) – and multiscale hydrological droughts, through the Standardized Flow Index (SFI). Based on a common threshold level for all indices, drought event statistics over the 50-yr period – number of events, duration, severity and magnitude – have been derived locally in order to highlight regional differences at multiple time scales and at multiple levels of the hydrological cycle. Independent spatio-temporal drought events have then been identified and described by combining local characteristics with the evolution of area under drought. Summary statistics have finally been used to compare past severe drought events, from multi-year precipitation deficits (1989–1990) to short hot and dry periods (2003). This multilevel and multiscale drought climatology will serve as a basis for assessing the impacts of climate change on droughts in France. Albergel, C., Rüdiger, C., Pellarin, T., Calvet, J.-C., Fritz, N., Froissard, F., Suquia, D., Petitpa, A., Piguet, B., and Martin, E.: From near-surface to root-zone soil moisture using an exponential filter: an assessment of the method based on in situ observations and model simulations, Hydrol. Earth Syst. Sci. Discuss., 5, 1603–1640, 2008. Andreadis, K M., Clark, E A., Wood, A W., Hamlet, A F., and Lettenmaier, D P.: Twentieth-century drought in the conterminous United States, J. Hydrometeorol., 6, 985–1001, doi:10.1175/JHM450.1, 2005. Baghdadi, N., Aubert, M., Cerdan, O., Franchistéguy, L., Viel, C., Martin, E., Zribi, M., and Desprats, J.-F.: Operational mapping of soil moisture using synthetic aperture radar data: application to the Touch basin (France), Sensors, 7, 2458–2483, doi:10.3390/s7102458, 2007. Bellocq, A.: La~sécheresse de l'automne 1978 en France – Aspect pluviométrique, La Météorologie, 16, 229–256, 1979. Besleaga, N.: La~sécheresse en France: 1976–1990 (Drought in France: 1976–1990, in French), no 1 in Phénom$\grave\rm e$nes remarquables, Direction de la Météorologie Nationale, Service Central Exploitation Météorologique, 1992. Bessemoulin, P., Bourdette, N., Courtier, P., and Manach, J.: La canicule d'ao$\hat\rm u$t 2003 en France et en Europe (The August 2003 heat wave in France and Europe, in French), La Météorologie, 46, 25–33, 2004. Blanchard, M., Franchistéguy, L., Habets, F., Martin, E., and Noilhan, J.: Typology of droughts over France and tools for estimation of water resources used at Météo-France, Rev. Fr. Géotech., 120–121, 11–20, 2007. Bordi, I., Fraedrich, K., Gerstengarbe, F.-W., Werner, P C., and Sutera, A.: Potential predictability of dry and wet periods: Sicily and Elbe-Basin (Germany), Theor. Appl. Climatol., 77, 125–138, doi:10.1007/s00704-003-0029-0, 2004. Bréda, N. and Badeau, V.: Forest tree responses to extreme drought and some biotic events: Towards a~selection according to hazard tolerance?, C. R. Géosci., 340, 651–662, doi: 10.1016/j.crte.2008.08.003, 2008. Bremond, R.: L'incidence du déficit de pluie sur l'écoulement des rivi$\grave\rm e$res (Effect of precipitation deficits on river flows, in French), Ponts Chauss. Mag., 12, 49–58, 1976. Briffa, K R., Jones, P D., and Hulme, M.: Summer moisture variability across Europe, 1892–1991 – An analysis based on the Palmer Drought Severity Index, Int. J. Climatol., 14, 475–506, doi:10.1002/joc.3370140502, 1994. Brochet, P.: Aspects climatiques de la sécheresse 1976 (Climatic aspects of the 1976 drought, in French), La~Météorologie, 7, 81–103, 1976. Brown, L D., Cai, T T., and DasGupta, A.: Interval estimation for a~binomial proportion, Stat. Sci., 16, 101–133, doi:10.1214/ss/1009213286, 2001. Buisson, G.: $\acute\rm E$valuation des co$\hat\rm u$ts des sécheresses au niveau national (National-scale cost assessment of droughts, in French), Lettre $\acute\rm E$valuationvaluation du Minist$\grave\rm e$re de l'Écologie, de l'Énergie, du Développement Durable et de l'Aménagement du Territoire, 8, 3–4, http://www.ecologie.gouv.fr/Lettre-Evaluation-no8-fevrier-2007.html, 2007. Choisnel, E.: Le bilan hydrique et le bilan d'énergie du sol (The soil water and energy budgets, in French), La~Météorologie, 11, 103–159, 1977. % Céron, J.-P., Tanguy, G., Franchistéguy, L., Martin, E., Regimbeau, F., and Vidal, J.-P.: Hydrological seasonal forecast over France: feasibility and potentialities, Atmos. Sci. Lett., accepted, 2009. de~Rosnay, P., Calvet, J.-C., Kerr, Y., Wigneron, J.-P., Lema$\hat\rm i$tre, F., Escorihuela, M J., Sabater, J M., Saleh, K., Barrié, J., Bouhours, G., Coret, L., Cherel, G., Dedieu, G., Durbe, R., Fritz, N. E D., Froissard, F., Hoedjes, J., Kruszewski, A., Lavenu, F., Suquia, D., and Waldteufel, P.: SMOSREX: A long term field campaign experiment for soil moisture and land surface processes remote sensing, Remote Sens. Environ., 102, 377–389, doi:10.1016/j.rse.2006.02.021, 2006. Direction de la Météorologie Nationale: Résumé mensuel du temps en France – Mars 1961 (Monthly weather summary in France – March 1961, in French), Tech. rep., Direction de la Météorologie Nationale, 1961. D'Odorico, P., Ridolfi, L., Porporato, A., and Rodriguez-Iturbe, I.: Preferential states of seasonal soil moisture: The impact of climate fluctuations, Water Res. Res., 36, 2209–2219, doi:10.1029/2000WR900103, 2000. Dutra, E., Viterbo, P., and Miranda, P. M A.: ERA-40 reanalysis hydrological applications in the characterization of regional drought, Geophys. Res. Lett., 35, L19402, doi:10.1029/2008GL035381, 2008. European Commission: Water Scarcity and Droughts: In-Depth Assessment, Interim Report 2, European Commission, http://ec.europa.eu/environment/water/quantity/pdf/comm_droughts/2nd_int_report.pdf, 2007. Gandin, L V.: Objective analysis of meteorological fields, Israel Program for Scientific Translations, Jerusalem, Israel, 242~pp., 1965. Guttman, N B.: Accepting the Standardized Precipitation Index: A calculation algorithm, J. Am. Water Res. Assoc., 35, 311–322, doi:10.1111/j.1752-1688.1999.tb03592.x, 1999. Habets, F., Noilhan, J., Golaz, C., Goutorbe, J.-P., Lacarr$\grave\rm e$re, P., Leblois, E., Ledoux, E., Martin, E., Ottlé, C., and Vidal-Madjar, D.: The ISBA surface scheme in a~macroscale hydrological model applied to the Hapex-Mobilhy area – Part II: Simulation of streamflows and annual water budget, J. Hydrol., 217, 97–118, doi:10.1016/S0022-1694(99)00020-7, 1999. Habets, F., Boone, A., Champeaux, J.-L., Etchevers, P., Franchistéguy, L., Leblois, E., Ledoux, E., Le~Moigne, P., Martin, E., Morel, S., Noilhan, J., Quintana~Segu\'i, P., Rousset-Regimbeau, F., and Viennot, P.: The SAFRAN-ISBA-MODCOU hydrometeorological model applied over France, J. Geophys. Res., 113, D06 113, doi:10.1029/2007JDOO8548, 2008. Hannaford, J., Lloyd-Hughes, B J., Keef, C., Parry, S., and Prudhomme, C P.: Examining the large-scale spatial coherence of European drought using regional indicators of rainfall and streamflow deficit, Hydrol. Proces., submitted, 2009. Hisdal, H. and Tallaksen, L M.: Estimation of regional meteorological and hydrological drought characteristics: a~case study for Denmark, J. Hydrol., 281, 230–247, doi:10.1016/S0022-1694(03)00233-6, 2003. Hisdal, H., Tallaksen, L M., Clausen, B., Peters, E., and Gustard, A.: Hydrological drought characteristics, in: Hydrological drought – Processes and estimation methods for streamflow and groundwater, vol 48 of Developments in Water Science, chap. 5, Elsevier, Amsterdam, The Netherlands, 139–198, 2004. Hosking, J. R M.: $L$-moments: analysis and estimation of distributions using linear combinations of order statistics, J. R. Stat. Soc. B, 52, 105–124, 1990. Koster, R D., Guo, Z., Dirmeyer, P A., Yang, R., Mitchell, K., and Puma, M J.: On the nature of soil moisture in land surface models, J. Clim., 22, 4322–4335, doi:10.1175/2009JCLI2832.1, 2009. Lana, X., Serra, C., and Burgueño, A.: Patterns of monthly rainfall shortage and excess in terms of the standardized precipitation index for Catalonia (NE Spain), Int. J. Climatol., 21, 1669–1691, doi:10.1002/joc.697, 2001. Larivi$\grave\rm e$re, G.: La~sécheresse en France en septembre 1985 (The drought in France in September 1985, in French), La~Météorologie, 10, p 54, 1985. Le~Roy~Ladurie, E.: Histoire humaine et comparée du climat, vol. III Le réchauffement de 1960 $\grave\rm a$ nos jours, Fayard, Paris, 461~pp., 2009. Ledoux, E., Girard, G., De~Marsily, G., and Deschenes, J.: Spatially distributed modeling: conceptual approach, coupling surface water and ground-water, in: Unsaturated flow hydrologic modeling: theory and practice, edited by: Morel-Saytoux, H J., vol. 275 of NATO ASI Series C, Kluwer, Norwell, Massachussets, 435–454, 1989. Liang, X., Lettenmaier, D P., Wood, E F., and J., B S.: A simple hydrologically based model of land-surface water and energy fluxes for general-circulation models, J. Geophys. Res., 99, 14415–14428, 1994. Lloyd-Hughes, B. and Saunders, M A.: A drought climatology for Europe, Int. J. Climatol., 22, 1571–1592, doi:10.1002/joc.846, 2002. Lloyd-Hughes, B., Hannaford, J., Parry, S., Keef, C., Prudhomme, C., and Rees, G.: The spatial coherence of European droughts – Stage 1: UK and European drought catalogues – Methodology, Science Report SC070079/SR1, Environment Agency, Bristol, UK, 2009a. Lloyd-Hughes, B., Hannaford, J., Parry, S., Keef, C., Prudhomme, C., and Rees, H G.: Drought catalogues for UK and Europe, Science Report SC070079/SR, Environment Agency, 2009b. Loukas, A. and Vasiliades, L.: Probabilistic analysis of drought spatiotemporal characteristics in Thessaly region, Greece, Nat. Hazards Earth Syst. Sci., 4, 719–731, 2004. L$\acute\rm o$pez-Moreno, J I., Vicente-Serrano, S M., Beguer\'ia, S., Garc\'ia-Ruiz, J M., Portela, M M., and Almeida, A B.: Dam effects on droughts magnitude and duration in a~transboundary basin: The Lower River Tagus, Spain and Portugal, Water Res., 45, W02 405, doi:10.1029/2008WR007198, 2009. Luterbacher, J., Dietrich, D., Xoplaki, E., Grosjean, M., and Wanner, H.: European seasonal and annual temperature variability, trends, and extremes since 1500, Science, 303, 1499–1503, doi:10.1126/science.1093877, 2004. Masson, V., Champeaux, J.-L., Chauvin, F., Meriguet, C., and Lacaze, R.: A global database of land surface parameters at 1-km resolution in meteorological and climate models, J. Clim., 16, 1261–1282, doi:10.1175/1520-0442(2003)16<1261:AGDOLS>2.0.CO;2, 2003. Maurer, E P., Wood, A W., Adam, J C., and Lettenmaier, D P.: A long-term hydrologically based dataset of land surface fluxes and states for the conterminous United States, J. Clim., 15, 3237–3251, doi:10.1175/1520-0442(2002)015<3237:ALTHBD>2.0.CO;2, 2002. McKee, T., Doesken, N., and Kleist, J.: The relationship of drought frequency and duration to time scales, in: Preprints of the 8th Conference on Applied Climatology, Anaheim, California, 179–184, 1993. McKee, T B., Doesken, N J., and Kleist, J.: Drought monitoring with multiple time scales, in: Preprints of the 9th Conference on Applied Climatology, Anaheim, California, 233–236, 1995. Mo, K C.: Model-based drought indices over the United States, J. Hydrometeorol., 9, 1212–1230, doi:10.1175/2008JHM1002.1, 2008. Moreau, F.: Drought crisis management: Loire basin example, La~Houille Blanche, 4, 70–76, doi:10.1051/lhb:200404010, 2004. Mounier, J.: Aspects et fréquences de la sécheresse en Bretagne~: essai de définition de la sécheresse en Europe océanique (Specificities and frequency of drought in Britanny: proposition for defining drought in the western coastal part of Europe, in French), Rev. Géogr. Lyon, 52, 167–176, 1977. Mérillon, Y. and Chaperon, P.: La~sécheresse de 1989 (The 1989 drought, in French), La~Houille Blanche, 325–339, 1990. Météo-France: Bulletin Climatique – Avril 1997 (Climate bulletin, April 1997, in French), Tech. rep., Météo-France, 12~pp., 1997. Noilhan, J. and Lacarrére, P.: GCM grids evaporation from mesoscale modeling, J. Clim., 8, 206–223, doi:10.1175/1520-0442(1995)008<0206:GGSEFM>2.0.CO;2, 1995. Noilhan, J. and Mahfouf, J.-F.: The ISBA land surface parameterisation scheme, Global Planet. Change, 13, 145–159, doi:10.1016/0921-8181(95)00043-7, 1996. Olden, J D. and Poff, N L.: Redundancy and the choice of hydrologic indices for characterizing streamflow regimes, River Res. Appl., 19, 101–121, doi:10.1002/rra.700, 2003. Palmer, W C.: Meteorological Drought, Research paper~45, US Department of Commerce, US Weather Bureau, Office of Climatology, Washington, DC, http://lwf.ncdc.noaa.gov/oa/climate/research/drought/palmer.pdf, 1965. Paris Anguela, T., Zribi, M., Hasenauer, S., Habets, F., and Loumagne, C.: Analysis of surface and root-zone soil moisture dynamics with ERS scatterometer and the hydrometeorological model SAFRAN-ISBA-MODCOU at Grand Morin watershed (France), Hydrol. Earth Syst. Sci., 12, 1415–1424, 2008. Piccarreta, M., Capolongo, D., and Boenzi, F.: Trend analysis of precipitation and drought in Basilicata from 1923 to 2000 within a~southern Italy context, Int. J. Climatol., 24, 907–922, doi: 10.1002/joc.1038, 2004. Prudhomme, C. and Sauquet, E.: Modelling a~Regional Drought Index in France, Euraqua report, CEH and Cemagref, Wallingford, UK and Lyon, France, http://nora.nerc.ac.uk/1366/1/EuraquaDroughtForecastingFinalReport.pdf, 2007. Quintana-Segu\'i, P., Le~Moigne, P., Durand, Y., Martin, E., Habets, F., Baillon, M., Canellas, C., Franchistéguy, L., and Morel, S.: Analysis of near-surface atmospheric variables: Validation of the SAFRAN analysis over France, J. Appl. Meteor. Climatol., 47, 92–107, doi:10.1175/2007JAMC1636.1, 2008. Rüdiger, C., Calvet, J.-C., Gruhier, C., Holmes, T. R H., De~Jeu, R. A M., and Wagner, W.: An intercomparison of ERS-Scat and AMSR-E soil moisture observations with model simulations over France, J. Hydrometeorol., 10, 431–447, doi:10.1175/2008JHM997.1, 2009. Rodriguez-Iturbe, I., Entekhabi, D., and Bras, R L.: Nonlinear dynamics of soil moisture at climate scales 1. Stochastic analysis, Water Res., 27, 1899–1906, 1991. Santos, M J., Ver\'issimo, R., Fernandes, S., Orlando, M., and Rodrigues, R.: Overview of regional meteorological drought analysis on Western Europe, Technical Report to the ARIDE project no 10, Instituto de $\acute\rm A$gua (INAG), Lisbon, Portugal, http://www.hydrology.uni-freiburg.de/forsch/aride/navigation/publications/pdfs/aride-techrep10.pdf, 2000. Santos, M J., Ver\'issimo, R., Fernandes, S., Orlando, M., and Rodrigues, R.: Meteorological droughts focused on a~pan-European context, in: FRIEND 2002 – REgional Hydrology: Bridging the Gap between Research and Practice, edited by: van Lanen, H. A J. and Demuth, S., no. 274 in IAHS Red Books, IAHS, Wallingford, UK, 273–280, 2002. Sauquet, E., Gottschalk, L., and Krasovskaia, I.: Estimating mean monthly runoff at ungauged locations: an application to France, Hydrol. Res., 39, 403–423, doi:10.2166/nh.2008.331, 2008. Sheffield, J. and Wood, E F.: Characteristics of global and regional drought, 1950–2000: Analysis of soil moisture data from off-line simulation of the terrestrial hydrologic cycle, J. Geophys. Res., 112, D17 115, doi:10.1029/2006JD008288, 2007. Sheffield, J., Goteti, G., Wen, F., and Wood, E F.: A simulated soil moisture based drought analysis for the United States, J. Geophys. Res., 109, D24 108, doi:10.1029/2004JD005182, 2004. Sheffield, J., Goteti, G., and Wood, E F.: Development of a~50-year high-resolution global dataset of meteorological forcings for land, J. Clim., 19, 3088–3111, doi:10.1175/JCLI3790.1, 2006. Sheffield, J., Andreadis, K M., Wood, E F., and Lettenmaier, D P.: Global and continental drought in the second half of the 20th century: severity-area-duration analysis and temporal variability of large-scale events, J. Clim., 22, 1962–1981, doi:10.1175/2008JCLI2722.1, 2009. Shukla, S. and Wood, A W.: Use of a~standardized runoff index for characterizing hydrologic drought, Geophys. Res. Lett., 35, doi:10.1029/2007GL032487, 2008. Snelder, T H., Lamouroux, N., Leathwick, J R., Pella, H., Sauquet, E., and Shankar, U.: Predictive mapping of the natural flow regimes of France, J. Hydrol., 373, 57–67, doi:10.1016/j.jhydrol.2009.04.011, 2009. Soubeyroux, J.-M., Martin, E., Franchistéguy, L., Habets, F., Noilhan, J., Baillon, M., Regimbeau, F., Vidal, J.-P., Le~Moigne, P., and Morel, S.: Safran-Isba-Modcou (SIM) – Un outil pour le suivi hydrométéorologique opérationnel et les études (A hydrometeorological tool for operational monitoring and research: the Safran-Isba-Modcou application, in French), La~Météorologie, 63, 40–45, 2008. Soulé, P T.: Spatial patterns of drought frequency and duration in the contiguous USA based on multiple drought event definitions, Int. J. Climatol., 12, 11–24, doi:10.1002/joc.3370120103, 1992. Stahl, K.: Hydrological drought – A study across Europe, PhD Thesis, Albert-Ludwigs-Universität Freiburg, http://www.freidok.uni-freiburg.de/volltexte/202/pdf/stahl-diss.pdf, 2001. Stahl, K. and Demuth, S.: Method for regional classification of streamflow drought series: Cluster analysis, Technical Report to the ARIDE Project no 1, Institute of Hydrology, University of Freiburg, Freiburg, Germany, 1999. Svoboda, M., LeComte, D., Hayes, M., Heim, R., Gleason, K., Angel, J., Rippey, B., Tinker, R., Palecki, M., Stooksbury, D., Miskus, D., and Stephens, S.: The drought monitor, Bull. Am. Meteor. Soc., 83, 1181–1190, doi:10.1175/1520-0477(2002)083<1181:TDM>2.3.CO;2, 2002. Tallaksen, L M., Hisdal, H., and van Lanen, A. J H.: Space-time modelling of catchment scale drought characteristics, J. Hydrol., 375, 363–372, doi:10.1016/j.jhydrol.2009.06.032, 2009. Trnka, M., Dubrovsk\'y, M., Svoboda, M., Semerádová, D., Hayes, M., Žalud, Z., and Wilhite, D.: Developing a~regional drought climatology for the Czech Republic, Int. J. Climatol., 29, 863–883, doi:10.1002/joc.1745, 2009. van~der Schrier, G., Efthymiadis, D., Briffa, K R., and Jones, P D.: European Alpine moisture variability for 1800–2003, International J. Climatol., 27, 415–427, doi:10.1002/joc.1411, 2007. Vautard, R., Yiou, P., D'Andrea, F., de~Noblet, N., Viovy, N., Cassou, C., Polcher, J., Ciais, P., Kageyama, M., and Fan, Y.: Summertime European heat and drought waves induced by wintertime Mediterranean rainfall deficit, Geophys. Res. Lett., 34, doi:10.1029/2006GL028001, 2007. Vicente-Serrano, S M.: Differences in spatial patterns of drought on different time scales: An analysis of the Iberian Peninsula, Water Res. Manage., 20, 37–60, doi:10.1007/s11269-006-2974-8, 2006. Vicente-Serrano, S. M. and L$\acute\rm o$pez-Moreno, J. I.: Hydrological response to different time scales of climatological drought: an evaluation of the Standardized Precipitation Index in a mountainous Mediterranean basin, Hydrol. Earth Syst. Sci., 9, 523–533, 2005. Vidal, J.-P. and Moisselin, J.-M.: Impact du changement climatique sur les sécheresses en France (Impact of climate change on droughts in France, in French), in: Actes du XXIe colloque de l'Association Internationale de Climatologie: Climat et risques climatiques en Méditerranée, edited by: Vinet, F., AIC, Montpellier, France, 655–660, 2008. Vidal, J.-P. and Soubeyroux, J.-M.: Impact du changement climatique en France sur la sécheresse et l'eau du sol (Impact of climate change on drought and soil moisture in France, in French), in: SEC 2008 – International Symposium – Drought and constructions, vol 1, edited by: Magnan, J.-P., Cojean, R., Cui, Y.-J., and Mestat, P., Laboratoire Central des Ponts et Chaussées, Marne-la-Vallée, France, 25–31, 2008. Vidal, J.-P. and Wade, S D.: A multimodel assessment of future climatological droughts in the UK, Int. J. Climatol., doi: 10.1002/joc.1843, in press, 2009. Vidal, J.-P., Martin, E., Baillon, M., Franchistéguy, L., and Soubeyroux, J.-M.: A 50-year high-resolution atmospheric reanalysis over France with the Safran system, Int. J. Climatol., in press, 2009. Wang, A., Bohn, T J., Mahanama, S P., Koster, R D., and Lettenmaier, D P.: Multimodel ensemble reconstruction of drought over the continental United States, J. Clim., 22, 2694–2712, doi:10.1175/2008JCLI2586.1, 2009. Wilhite, D A. and Glantz, M H.: Understanding the drought phenomenon: The role of definitions., Water Int., 10, 111–120, 1985. Wilks, D S.: Statistical methods in the atmospheric sciences, vol 91 of International Geophysics Series, Academic Press, New York, 2nd edn., 2006. WMO: Manual for depth-area-duration analysis of storm precipitation, Tech. Rep. 237.TP.129, World Meteorological Organization, Geneva, Switzerland, 1969. Zaidman, M D. and Rees, H G.: Spatial patterns of streamflow drought in Western Europe 1960–1995, Technical Report to the ARIDE project no 8, Centre for Ecology and Hydrology, Wallingford, UK, http://www.hydrology.uni-freiburg.de/forsch/aride/navigation/publications/pdfs/aride-techrep8.pdf, 2000. Zaidman, M. D., Rees, H. G., and Young, A. R.: Spatio-temporal development of streamflow droughts in north-west Europe, Hydrol. Earth Syst. Sci., 6, 733–751, 2002.