Intra-seasonal rainfall variability during the maize growing season in the northern lowlands of Lesotho Mphethe Isaac Tongwane & Mokhele Edmond Moeletsi
Theoretical and Applied Climatology ISSN 0177-798X Volume 120 Combined 3-4 Theor Appl Climatol (2015) 120:575-585 DOI 10.1007/s00704-014-1183-2
1 23
Your article is protected by copyright and all rights are held exclusively by SpringerVerlag Wien. This e-offprint is for personal use only and shall not be self-archived in electronic repositories. If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the original source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com”.
1 23
Author's personal copy Theor Appl Climatol (2015) 120:575–585 DOI 10.1007/s00704-014-1183-2
ORIGINAL PAPER
Intra-seasonal rainfall variability during the maize growing season in the northern lowlands of Lesotho Mphethe Isaac Tongwane & Mokhele Edmond Moeletsi
Received: 19 December 2013 / Accepted: 23 May 2014 / Published online: 18 June 2014 # Springer-Verlag Wien 2014
Abstract Intra-seasonal rainfall distribution was identified as a priority gap that needs to be addressed for southern Africa to cope with agro-meteorological risks. The region in the northwest of Lesotho is appropriate for crop cultivation due to its relatively favourable climatic conditions and soils. High rainfall variability is often blamed for poor agricultural production in this region. This study aims to determine the onset of rains, cessation of rains and rainy season duration using historical climate data. Temporal variability of these rainy season characteristics was also investigated. The earliest and latest onset dates of the rainy season are during the last week of October at Butha-Buthe and the third week of November at Mapoteng, respectively. Cessation of the season is predominantly in the first week of April making the season approximately 137–163 days long depending on the location. Average seasonal rainfall ranged from 474 mm at Mapoteng to 668 mm at Butha-Buthe. Onset and cessation of the rainfall season vary by 4–7 weeks and 1 week, respectively. Mean coefficient of variation of seasonal rainfall is 39 %, but monthly variations are higher. These variations make annual crop management and planning difficult each year. Trends show a decrease in the rainfall amounts but improvements in both the temporal distribution of annual rainfall, onset and cessation dates.
1 Introduction Rainfall in Lesotho and southern Africa is strongly determined by a number of atmospheric circulation patterns (Usman and M. I. Tongwane (*) : M. E. Moeletsi Agricultural Research Council, Institute for Soil, Climate and Water, Private Bag X79, Pretoria 0001, South Africa e-mail:
[email protected] M. E. Moeletsi Risks and Vulnerability Assessment Centre, University of Limpopo, Private Bag X1106, Sovenga 0727, South Africa
Reason 2004; Reason et al. 2006a; Davis 2011). The most favourable rainfall conditions over most of the region are provided by tropical temperate troughs extending from the west of the subcontinent forming large-scale bands of clouds (Usman and Reason 2004; Todd et al. 2004; Pohl et al. 2009). However, the occurrence of the Botswana Upper High pressure system can result in drought in Lesotho and southern Africa as a whole (Garanganga 2007; Davis 2011). Much of the central and subtropical subcontinent receives more than 60 % of its annual rainfall during the December–February period (Engelbrecht et al. 2009). During winter, the subtropical high-pressure belt is well-established over southern Africa resulting in limited rainfall in Lesotho (Johnsson 2004; Engelbrecht et al. 2009; Engelbrecht and Landman 2010). Winter rainfall is mostly attributed to the transient moisture from the mid-latitude cold fronts originating from the Atlantic Ocean. Lesotho receives approximately 85 % of its total rainfall in summer (October–April) and the remaining 15 % in winter (Ministry of Natural Resources 2000). Lesotho’s precipitation is characterized by high climate variability from year to year. The dominant climatic mode responsible for seasonal rainfall variability across central southern Africa has been pointed out to be the El-Nino Southern Oscillation (Manatsa et al. 2008). Besides the variability in climate, topography imposes severe constraints on crop production. In Lesotho, the consequences of large variability in climatic conditions and topography have led to great differences in agro-ecological zones (Lowlands, Highlands, Foothills and Senqu River Valley) and agricultural production (Moeletsi and Walker 2013). The lowlands are geographically situated on the western part of the country along the border with South Africa and can be further divided into two parts: northern and southern lowlands. Together with the foothills, the lowlands are areas of higher agricultural potential in the country (Dejene et al. 2011). The northern lowlands are the main agricultural production areas mainly
Author's personal copy 576
due to conducive environmental conditions (Crop and Food Security Assessment Mission 2006). They are characterized by relatively more seasonal rainfall and less variability than the southern lowlands and all the other zones. The other zones are more prone to severe dry spells during the main crop growing season. The prominent factors brought by the climate variability are the recurrent dry spells and hailstorms during the cropping season, heavy rainfall that causes soil erosion and frosts that damage the late planted crops mainly in the foothills and highlands. The combination of poor land use practices, rainfall regime and its variability promotes land degradation in the country which is already characterized by fragile alpine ecosystems. In addition to rainfall variability, there is increasing concern in southern Africa about the possible decline of rainfall as a result of global warming (Mazvimavi 2010). Decline in rainfall in the subcontinent and Lesotho in particular can have negative impacts that will compound to national food insecurity. Maize is the major source of food in southern Africa. In Lesotho, Malawi, South Africa, Zambia and Zimbabwe, the average consumption is over 100 kg/capita/year, amounting to more than 50 % of total calories in Lesotho, Malawi and Zambia; 43 % in Zimbabwe; and 31 % in South Africa (Shiferaw et al. 2011). However, a limited 0.2 % of agricultural land in Lesotho is permanently allocated to crop production (FAO 2013). National statistical reports show that in recent years, the northern lowlands (area extending from Berea to Butha-Buthe in this study) cultivated on average 30 % of the land planted with maize in the country (Bureau of Statistics 2010, 2012). Maize yields in metric tonnes per hectare have been on a decline since the beginning of the century from the average (0.5
