VariationsV6N3 12/9/08 11:56 AM Page 1 us CLIVAR U.S. CLIVAR December 2008, Vol. 6, No. 3 VARIATIONS Drought Reigns Summer Drought and Heat Waves in by David M. Legler, Director Southern Africa: Observations and recent workshop in Lincoln, Nebraska on Drought turned Coupled Model Behavior Aout to be a tremendously interesting and unprecedented gath- Bradfield Lyon ering of the operational modeling International Research Institute for Climate and Society, and forecasting community (e.g. Columbia University, NY, NY NCEP), those who deve lop rou- tine/operational products and out- tively correlated is of course well looks (e.g. NCEP, the National uring the severe summer known with the physical linkage being Drought Mitigation Ce nter), and the drought of 1991-92 in via changes in the surface energy budg- research community who are help- southern Africa it is esti- et. Drier-than-average conditions reduce ing to provide new insight and mated that as much as 3 soil moisture favoring an increase in the deve lop new capabilities. Working Dmillion tons of grain production were surface sensible heat flux and thus high- together and in harmony, these lost in this predominately rain-fed agri- er surface air temperature. In southern groups are mining for improve d cultural region (Dilley and Heyman Africa the tendency for below-average predictability of long-term drought, 1995). The extreme high temperatures rainfall and above-average temperatures exploring the causes of drought, that accompanied the drought not only are often seen, for example, during El and discussing how best to improve contributed to the crop losses but also to Niño events which tend to be associated the products and knowledge that widespread livestock mortality with the near-synchronous occurrence can be conveyed through a suite of (Sivakumar 2006) and stresses on of deficient rainfall and elevated surface services. regional water supplies (IPCC 2001). air temperatures on the seasonal time The joint occurrence of these two cli- scale (as in 1991-92). However, the rela- This issue of Variations pro- mate extremes is of consequence in any tionship between shorter periods (i.e. vides examples of some of the find- region of the globe although research several days) of extreme high tempera- ings of the US CL IVAR Drought has largely focused on the two phenom- tures (heat waves) and the occurrence of Working Group. The model runs the ena considered in isolation. As part of meteorological drought is less clear as Working Group deve loped are now the U.S. CLIVAR-led Drought in daily maximum temperatures are also ava ilable for anyone to analyze , Coupled Models Project (DRiCOMP) a affected by variations in cloud cover, and since they are global runs, they study was undertaken to examine how proximity to large water bodies, prevail- are a potential source of new well climate models have performed in ing wind direction, thermal advection, knowledge about drought in many simulating the observed climate of the etc. Indeed, for some coastal locations regions of the world. Working 20th Century with respect to generating of southern Africa, this study finds that Group members are preparing drought, heat waves and their joint heat waves often occur in association nearly ten manuscripts describing occurrence. The models were then uti- with strong downslope flow generated lized to assess, at least within (a subset Continued on Page Two by propagating synoptic weather sys- of) coupled climate model space, how tems which are distinct from the larger the concomitant occurrence of heat scale anomalous atmospheric circula- IN THIS ISSUE waves and drought may change under tion associated with drought (not Summer Drought and Heat Waves in Africa increasing anthropogenic forcing. The shown). ...................................................................1 primary focus was on the subcontinent The joint occurrence of heat waves Drought Working Group Activities...........4 of southern Africa. and drought is also confounded by the Analysis of Drought Simulations ............6 On monthly and seasonal time prospect of climate change. For exam- Carribean Low Level Jet ..........................8 scales the tendency for summer rainfall ple, climate change scenarios are in gen- Calendar ..................................................12 and surface air temperature to be nega- eral agreement that land surface temper- U.S. CLIMATE VARIABILITY AND PREDICTABILITY (CLIVAR) 1717 Pennsylvania Avenue, NW, Suite 250, Washington, DC 20006• www.usclivar.org VariationsV6N3 12/9/08 11:56 AM Page 2 Continued from Page One U.S. CLIVAR their analysis indicating predictability atures will increase in the 21st Century, heat wave was defined as a period of at of major SST patterns and trends, as generally increasing the probability of least 3 consecutive days with the daily well as soil moisture. Pe gion and extreme daily temperatures (though not maximum surface air temperature (Tmax) Kumar present one such effort in this necessarily in a spatially uniform manner, exceeding the 90th percentile during the issue. Another highlight of the e.g., Meehl and Tibaldi 2004). Yet these D e c e m b e r-Fe bruary season. The T m a x Workshop was reviewing the findings same models diverge considerably in percentiles were obtained by ranking the of the Drought in Coupled Models their projected changes in precipitation, daily data over the periods 1961-2000, (DRICOM P) funded research activi- which in the case of southern Africa has 1981-2000, 2046-65 and 2081-2100. ties. They inve stigated mechanisms some showing a drier, and others wetter, Drought conditions were based on differ- important for drought. Ke rry Cook’s climate compared with the 20th century ent indicators including the three month paper in this issue focuses on the role (IPCC 2007). Therefore, in the coming Standardized Precipitation Index (SPI3), of the Caribbean Lo w Leve l Jet in century there could potentially be more a related standardized drought index regional drought. U.S .CLIVAR’s activ- heat waves even in regions with upward (WASP, Lyon and Barnston 2005), and ities in drought are now ready to be trends in rainfall (even in the absence of one based on precipitation minus evapo- documented and published. Watch drought), or decreased precipitation may ration (P-E). Observational data included for 13 manuscripts from DRI COMP lead to more frequent droughts, favoring daily maximum temperatures for stations PIs and others who attending the the joint occurrence of heat waves via across South Africa for 1961-2000 and Drought Workshop, along with the changes in surface heat fluxes. gridded monthly precipitation analyses Working Group manuscripts, that will The models utilized in the study were obtained from the Global Precipitation be collected into a special issue of primarily the GFDL2.0, ECHAM5, and Climatology Center (GPCC) for the same the Journal of Climate. CSIRO3.5 all of which were included in period. Drought-related research is the Coupled Model Intercomparison The observational results are general- not complete though. Much more Project (CMIP-3), their output data ly well-captured by the station analysis could be done to understand the cou- archived at the Program for Climate shown in Figure 1 for Kimberley, South pled ocean-atmosphere-land nature Model Diagnosis and Intercomparison Africa located in the central interior of the of drought and its forcings. (PCMDI) website. For comparison with country (see Figure 2c). The uncondi- Moreove r, we don’t fully know how observations the 20th Century Climate in tional probability (relative frequency of well long-term drought can be pre- Coupled Model (20C3M) runs were uti- occurrence) of a heat wave occurring dur- dicted and we have n’t yet fully con- lized. Climate change projections were ing any given month is 0.32. The proba- sidered how to develop early warn- based on output from the same models bility of drought, defined as occurring ing capabilities for drought and its forced with the A1B greenhouse gas sce- when SPI3 is < -1.0, is 0.16. However, evo lution. There is no doubt drought nario. The selection of the three models the conditional probability of a heat wave research will remain critical for used here was based on their general abil- occurring given that drought conditions advancing our capabilities. Only by ity to generate realistic ENSO character- exist is 0.77 or about 2.4 times the uncon- working with our colleagues in istics (e.g., AchutaRao and Sperber 2006) ditional probability (the conditional prob- GEWEX, and with the operational while also having daily maximum surface ability at Kimberley is greater than at sev- and observa tions/products communi- air temperature (and other) data available eral other stations, cf. Figure 2a, but in ties will we continue to make for both the 20C3M and A1B runs. A general it exceeds the unconditional prob- advancements that translate into improved products and services. Variations Published three times per year U.S. CLIVAR Office 1717 Pennsylvania Ave., NW Suite 250, Washington, DC 20006 (202) 419-3471 [email protected] Staff: Dr. David M. Legler, Editor Cathy Stephens, Assistant Editor and Staff Writer © 2008 U.S. CLIVAR Permission to use any scientific material (text and fig - Figure 1. Times series of SPI3 (bars) and occurrence of heat waves (red dots) for ures) published in this Newsletter should be obtained individual months of the DJF seasons 1960-2000 at Kimberley, South Africa. The from the respective authors. Reference to newsletter materials should appear as follows: AUTHORS, year. solid line represents the SST anomaly averaged over the Nino3.4 region. The Title, U.S. CLIVAR Newsletter, No. pp. (unpublished correlation between Nino3.4 SST anomaly and SPI3 is -0.53. The Pr(Heat Wave) manuscript). This newsletter is supported through contributions to = 0.32; Pr(Drought SPI < -1) = 0.16, Pr(Heat Wave | Drought) = 0.77.