The objective of this study was to characterise meteorological droughts in the Central Region of South Africa using Standardised Precipitation Evapotranspiration Index (SPEI) and to examine if there is a relationship between drought and El Ni？o events. The SPEI was used to quantify the precipitation deficit over time and space across the catchment for the time-scales that are important for planning and management of water resources. Based on 12-month time-scale, the total number of drought events identified in the area using SPEI ranged between 13 and 20 during the period of analysis (1952–1999). Considering the effects of event magnitude and duration as severity parameters, the most severe drought event was identified during 1973 followed by 1995 based on 12-month time-scale. Moreover, it was also found that the number of moderate, severe, and extreme drought events identified by SPEI follows increasing trend with decade during the period of analysis. Results of Spearman’s rank correlation test revealed that the trends exhibited by mild (SPEI-3 and SPEI-6), moderate (SPEI-12), severe (SPEI-12), and extreme (SPEI-3) drought categories are statistically significant at 5% significance level. The study also revealed that drought events in the central region of South Africa are preceded by El Ni？o events in the tropical Pacific (Nino 3.4) with an average lag time of 8 months between the onsets of the two events. It was found that hydrological drought events in the study area lag behind meteorological drought events with an average lag time of 7.4 months. Findings of this study can be used to forecast drought events in the area for the proper planning and management of water resources. 1. Introduction It is well established that precipitation characteristics have changed, and they will continue to change towards more intense and intermittent spells [1]. This translates into more frequent and more severe water-related extreme events. For example, Rouault and Richard [2] reported an increase in the spatial extent of drought in southern Africa since the 1970s due to stronger relationship between El Ni？o Southern Oscillation (ENSO) and the southern African rainfall. Janowiak [3] reported that positive rainfall departures in equatorial East Africa and negative departures in South Africa followed ENSO events. Nicholson and Kim [4] made a comprehensive assessment of the rainfall response to ENSO episodes over Africa and reported that the strongest signals have appeared in southern, eastern, and far northern Africa and the weakest in the Sahel. Nicholson and
References
[1]
S. P. Simonovic, Managing Water Resources: Methods and Tools for a Systems Approach, UNESCO, Paris, France; Earthscan James & James, London, UK, 2009.
[2]
M. Rouault and Y. Richard, “Intensity and spatial extent of droughts in southern Africa,” Geophysical Research Letters, vol. 32, no. 15, Article ID L15702, 2005.
[3]
J. Janowiak, “An investigation of interannual rainfall variability in Africa,” Journal of Climate, vol. 1, no. 3, pp. 240–255, 1988.
[4]
S. E. Nicholson and J. Kim, “The relationship of the El Ni？o/Southern Oscillation to African rainfall,” International Journal of Climatology, vol. 17, pp. 117–135, 1997.
[5]
S. E. Nicholson and D. Entekhabi, “Rainfall variability in equatorial and southern Africa: relationships with sea surface temperatures along the southwestern coast of Africa,” Journal of Climate & Applied Meteorology, vol. 26, no. 5, pp. 561–578, 1987.
[6]
S. E. Nicholson, “An analysis of the ENSO signal in the tropical Atlantic and western Indian Oceans,” International Journal of Climatology, vol. 17, no. 4, pp. 345–375, 1997.
[7]
C. J. C. Reason and M. Rouault, “ENSO-like decadal variability and South African rainfall,” Geophysical Research Letters, vol. 29, no. 13, pp. 1–4, 2002.
[8]
M. Rouault, P. Florenchie, N. Fauchereau, and C. J. C. Reason, “South East tropical Atlantic warm events and Southern African rainfall,” Geophysical Research Letters, vol. 30, no. 5, pp. 9–4, 2003.
[9]
C. J. C. Reason, S. Hachigonta, and R. F. Phaladi, “Interannual variability in rainy season characteristics over the Limpopo region of southern Africa,” International Journal of Climatology, vol. 25, no. 14, pp. 1835–1853, 2005.
[10]
F. D. Richardson, B. D. Hahn, and M. T. Hoffman, “Modelling the sustainability and productivity of pastoral systems in the communal areas of Namaqualand,” Journal of Arid Environments, vol. 70, no. 4, pp. 701–717, 2007.
[11]
S. Vetter, “Drought, change and resilience in south africa's arid and semi-arid rangelands,” South African Journal of Science, vol. 105, no. 1-2, pp. 29–33, 2009.
[12]
C. Vogel, “(Mis)management of droughts in South Africa,” South African Journal of Science, vol. 90, pp. 4–6, 1994.
[13]
J. E. Ellis and D. M. Swift, “Stability of African pastoral ecosystems: alternate paradigms and implications for development,” Journal of Range Management, vol. 41, no. 6, pp. 450–459, 1988.
[14]
M. Burns, M. Audouin, and A. Weaver, “Advancing sustainability science in South Africa,” South African Journal of Science, vol. 102, no. 9-10, pp. 379–384, 2006.
[15]
C. Seymour and P. Desmet, “Coping with drought: do science and policy agree?” South African Journal of Science, vol. 105, no. 1-2, pp. 18–19, 2009.
[16]
R. R. Heim Jr., “A review of twentieth-century drought indices used in the United States,” Bulletin of the American Meteorological Society, vol. 83, no. 8, pp. 1149–1165, 2002.
[17]
V. U. Smakhtin and D. A. Hughes, “Review, automated estimation and analyses of drought indices in South Asia,” IWMI Working Paper N 83-Drought Series Paper N 1, Colombo, Sri Lanka, 2004.
[18]
L. G. Du Pisani, H. J. Fouché, and J. C. Venter, “Assessing rangeland drought in South Africa,” Agricultural Systems, vol. 57, no. 3, pp. 367–380, 1998.
[19]
S. M. Vicente-Serrano and J. I. López-Moreno, “Hydrological response to different time scales of climatological drought: an evaluation of the Standardized Precipitation Index in a mountainous Mediterranean basin,” Hydrology and Earth System Sciences, vol. 9, no. 5, pp. 523–533, 2005.
[20]
D. C. Edossa, M. S. Babel, and A. D. Gupta, “Drought analysis in the Awash River Basin, Ethiopia,” Water Resources Management, vol. 24, no. 7, pp. 1441–1460, 2010.
[21]
F. Fiorillo and F. M. Guadagno, “Karst spring discharges analysis in relation to drought periods, using the SPI,” Water Resources Management, vol. 24, no. 9, pp. 1867–1884, 2010.
[22]
L. Vasiliades and A. Loukas, “Hydrological response to meteorological drought using the Palmer drought indices in Thessaly, Greece,” Desalination, vol. 237, no. 1–3, pp. 3–21, 2009.
[23]
J. Lorenzo-Lacruz, S. M. Vicente-Serrano, J. I. López-Moreno, S. Beguería, J. M. García-Ruiz, and J. M. Cuadrat, “The impact of droughts and water management on various hydrological systems in the headwaters of the Tagus River (central Spain),” Journal of Hydrology, vol. 386, no. 1–4, pp. 13–26, 2010.
[24]
Y. E. Woyessa, W. A. Welderufael, J. D. M. Kinyua, G. Kundhlande, and O. P. Tsumake, “Land-water linkages: agent-based modelling of land use and its impact on water resources,” Water Research Commission Report No. 1753/1/10, 2011.
[25]
W. A. Welderufael, Y. E. Woyessa, and D. C. Edossa, “Impact of rainwater harvesting on water resources of the modder river basin, central region of South Africa,” Agricultural Water Management, vol. 116, pp. 218–227, 2013.
[26]
S. D. Lynch, “The development of a raster database of annual, monthly and daily rainfall for Southern Africa,” Report 1156/1/04, Water Research Commission, Pretoria, South Africa, 2004.
[27]
C. W. Thornthwaite, “An approach toward a rational classification of climate,” Geographical Review, vol. 38, no. 1, pp. 55–94, 1948.
[28]
L. Vermes, How to Work out a Drought Mitigation Strategy, ICID Guide, 309/1998, Bonn, Germany, 1998.
[29]
L. T. Dube and M. R. Jury, “Structure and precursors of the 1992/93 drought in KwaZulu-Natal, South Africa from NCEP reanalysis data,” Water SA, vol. 29, no. 2, pp. 201–207, 2003.
