Agroclimatological risk assessment of rainfed maize production for the Free State Province of South Africa

Abstract

English: The risks associated with climate and its variability over the Free State Province is the major determining factor for agricultural productivity, and has a major impact on food security across the province. To improve productivity of agricultural lands, producers and decisions makers have to be provided with relevant agrometeorological information that will enable them to make appropriate decisions. This has lead to the investigation of this agroclimatological risk assessment for maize production in the Free State. The ultimate goal was to characterize the agroclimatological risks impacting negatively on dryland maize production and develop a climate risk tool that will assist the stakeholders in their management of agricultural lands. First, meteorological data needed to perform this study was prepared by looking specifically at filling the missing data gaps and using alternative data in cases where measured data was not available to obtain good spatial distribution of weather stations. Frost was identified as one of the climate hazards affecting the maize plant in the Free State. Three frost severity categories were analysed, namely 2°C, 0°C and -2°C representing light, medium and heavy frost respectively. The onset of frost for all the thresholds was earlier over the northern, eastern and far southeastern parts of the Free State province while places over the western and southwestern parts of the province the first frost dates are later. The northern and eastern parts are also marked by late cessation of frost giving a shorter frost-free period (220-240 days at medium frost severity). The western and southwestern areas mostly have earlier cessation of frost resulting in relatively long frostfree period with ranges from 241 to 300 days at medium frost severity level. Cessation of frost occurring later than normal over the Free State can impact negatively on the maize crop if planted in October and early November, especially over the highlands. Productivity of the crops can also be hampered by earlier than normal onset of frost that affects maize at silking and grain-filling stages. The onsets and cessation of rains together with the duration of the rainy season also play an important role in agricultural planning. Over 300 stations across the Free State were analysed to characterize the rainy season. The onsets of rains were found to be early over the eastern parts of the province with median onsets on or earlier than 10 October. In most areas over the Fezile Dabi and Motheo districts, onsets are between 11 to 30 October while over the Lejweleputswa onsets are mostly between 21 October and 10 November. Most of the western parts of Xhariep experience later than 21 November at 50% risk level. The cessation of rains does not vary much over the Free State with most places having their median last rains between 21 April and 30 April. Rainy season lengths are longer over the Thabo Mofutsanyane district with over 200 days in some places. The ENSO episodes are related to Free State seasonal rainfall variability but only have slight effect on the cessation of rains while onsets of rains showed no differences between El Niño or La Niña phases as compared to all the years. In El Niño years the seasonal rainfall amount is lower than normal, being higher than normal in La Niña years which support findings from other studies. The cessation of rains occurs earlier in El Niño years and later than normal in La Niña years. Agricultural drought is one of the most devastating hazards affecting maize production in most growing periods depending on the location. It is important to plant during periods which minimise drought conditions. In this study a simple water balance model developed by FAO called WRSI was used to quantify drought risk. When using the 120-day maize cultivar as a reference, drought index over most parts of the Lejweleputswa, Xhariep and eastern parts of the Motheo district show high vulnerability (WRSI<40) for October planting dates while other areas have relatively low risk of drought. In December and January planting dates drought index over most parts of the province showed much improvement but places that showed low risk are over the Thabo Mofutsanyane, Fezile Dabi and pockets of northern Lejweleputswa district. Poone AgroClimatic Suitability Index (PACSI) was introduced to integrate all the climate hazards affecting maize production in the Free State. The index in made from the combination of frost probability over the growing period, non-exceedence probability of onset of rains and agricultural drought index. The index was further used to delineate the suitable areas across the Free State for planting maize variety requiring 1420 growing degree days (heat units) to maturity. The findings obtained from the resulting maps show areas of high maize production suitability over the Thabo Mofutsanyane district for mid-October to early November planting dates. Places over Fezile Dabi and northern parts of the Lejweleputswa district also showed high suitability of maize especially for planting from mid-November to end of December. The western and southern Xhariep district area is not suitable for planting maize while other marginal dryland maize production areas include western Motheo, southwestern Lejweleputswa and most parts of the central and eastern Xhariep. To conclude the study, the Free State Maize Agroclimatological Risk Tool (FS-MACRT) was developed to provide agroclimatological risk information important to the production of rainfed maize in the Free State Province. The tool is to be used by the farmers, extension officers, policy-makers and agricultural risk advisors. The tool has two main parts, 1) climatological risk and 2) forecasting. The climatological risk enables the user to obtain drought stress risk for the 100-day, 120-day and 140-day maize cultivars for planting window starting in October to January. The best planting dates based on the risk associated with the climatology onset and cessation of both rains and frost can be determined. Using climate forecasts obtained from the national forecasting centres, drought index can be predicted for different planting dates giving the farmer valuable information when planning for the coming season. The tool also has the functionality of predicting onsets of rains using weather and climate forecasts.

Afrikaans: Die risikos wat geassosieer word met klimaat en die variasies in die Vrystaat provinsie is die hoof faktor wat landbou produksie beïnvloed en het „n groot impak op die voedsel sekuriteit. Om die produktiwiteit van die landbou produsente en die besluitmakers te verhoog moet die nodige agrometeorologiese inligting aan hulle verskaf word sodat die regte besluite geneem kan word. Dit het aanleiding gegee tot die ondersoek na die agroklimatologiese risiko assessering van mielie produksie in die Vrystaat. Die hoof doel was om die agroklimatologiese risiko te karakteriseer asook die negatiewe impak op droëland mielies en dan sodoende „n klimaat risiko instrument te ontwikkel wat kan help met die bestuur van hulle lande. Vir die studie is meteorologiese data voorberei deur die vermiste data te vervang met alternatiewe data waar geen gemete data beskikbaar was nie om die regte ruimtelike verspreiding van weerstasies te verkry. Ryp is geïdentifiseer as een van die klimaats hindernisse wat mielies beïnvloed in die Vrystaat. Drie hewige ryp kategoriee is geanaliseer naamlik 2oC, 0oC en -2oC wat ligte, medium en hewig ryp voorstel. Die eerste tekens van ryp begin in die noordelike, oostelike en ver suidoostelike dele van die Vrystaat waar ryp in die westelike en suidwestelike dele later voorkom. Die noordelike en oostelike dele word ook gekenmerk deur ryp op „n latere stadium wat aanleiding gee tot „n korter rypvrye periode (220-240 dae met medium ryp). In die westelike en suidwestelike dele vroeëre staking van ryp gee aanleiding tot in „n langer rypvrye periode wat wissel tussen 241-300 dae van medium ryp. Wanneer ryp later as gewoonlik voorkom in die Vrystaat het dit „n negatiewe impak op mielieproduksie in Oktober en begin November veral in die hooglande. Die produktiwiteit van gewasse kan ook gerem word deur ryp wat vroeër as gewoonlik plaasvind en dit kan die mieliebaard en graanvul period beïnvloed. Die begin, einde en periode van reën speel „n belangrike rol in landbou beplanning. Oor die 300 weerstasies in die Vrystaat is geanaliseer om die reënseisoen te karakteriseer. Die begin van die reënseisoen is vroeër in die oostelike dele van die provinsie terwyl die middelste gedeelte se reën om en by 10 Oktober begin. In die Fezile Dabi en Motheo distrikte begin die reënseisoen gewoonlik tussen 11 tot 30 Oktober, terwyl Lejweleputswa begin tussen 21 Oktober en 10 November. In Xhariep se westelike areas kom reën gewoonlik later as 21 November voor met „n 50 % risiko vlak. Die einde van die reënseisoen wissel nie baie in die provinsie nie, maar die meeste reën kom voor tussen 21 April en 30 April. Die langste reënseisoen kom voor in die omgewing van die Thabo Mofutsanyane distrik met meer as 200 dae in sommige dele. Die ENSO episodes is verwant aan die wisselende seisonale reënval maar het „n geringe effek op die einde van die reën periode terwyl die begin van die reënseisoen geen verskille toon tussen El Niño of La Niña tussen verskillende jare nie. Gedurende die El Niño jare is die seisonale reënval laer as normal, terwyl dit in die La Niña jare weer hoër is, wat verskeie studies ondersteun. Die einde van die reënseisoen is vroeër in El Niño years en later as normaal in La Niña jare. Droogte is een van die mees verwoestend gevare wat mielie produksie gedurende die groeiseisoen kan affekteer afhangende van die lokaliteit. Dit is belangrik om te plant gedurende periods met minimum droeër kondisies. In die studie is gebruik gemaak van „n eenvoudige water model bekend as WRSI wat ontwikkel is deur FAO om droogte risiko te kwantifiseer. Wanneer die 120-dae mielie kultivar as verwysing gebruik word, dui die droogte indeks aan dat die meeste dele van Lejweleputswa, Xhariep en die oostelike dele van die Motheo distrik vatbaar is vir droogte (WRSI<40) gedurende Oktober se planttye terwyl ander areas „n laer risiko het. Gedurende Desember en Januarie is die droogte plant indeks beter oor die grootste gedeelte van die provinsie met laer risikos oor Thabo Mofutsanyane, Fezile Dabi en dele van die noordelike Lejweleputswa distrik. Die Poone AgroClimatic Suitability Indeks (PACSI) is bekendgestel om alle klimaatsgevare te integreer wat mielie produksie in die Vrystaat kan beïnvloed.Die indeks bestaan uit „n kombinasie van die waarskynlikheid van ryp gedurende die groeiperiode, die waarskynlikheid van reën en die droogte indeks. Die indeks was ook gebruik om die regte areas oor die Vrystaat te skets om mielievariasies te plant wat 1420 dae (hitte eenhede) nodig het om volwassenheid te bereik. Die resultate toon areas met „n hoë mielie produksie oor die Thabo Mofutsanyane distrik van middel Oktober tot begin November. Dele van Fezile Dabi en die noordelike dele van Lejweleputswa distrik is ook hoogs geskik vir produksie van middel November tot einde Desember. Die westelike en suidelike Xhariep distrik is nie geskik vir mielie produksie nie terwyl matige droëland mielie produksie areas insluit die westelike dele van Motheo, suidwestelike Lejweleputswa en die meeste dele van sentrale en oostelike Xhariep. Gevolglik is die Vrystaatse Mielie Agroklimaats Risiko Apparaat (VS-MAKRA) ontwikkel om agroklimaatsrisiko inligting te verskaf vir die produksie van droëland mielies in die Vrystaat. Die apparaat moet gebruik word deur boere, voorligtingsbeamptes, landboupolishouers en landbou risiko adviseurs. Die apparaat het twee hoof dele, 1) klimaatrisiko en 2) voorspelling. Die klimaatrisiko stel die gebruiker in staat om „n droogte stres risiko te bepaal vir 100, 120 en 140 dag mielie kultivars gedurende die plant periode vanaf begin Oktober tot Januarie. Die beste plant datums gebaseer op die risiko geassosieer met die klimatologiese begin en einde van reën en ryp kan voorspel word. Deur gebruik te maak van voorspellings kan die droogte indeks voorspel word vir verskillende plant datums, wat dan waardevolle inligting vir die opvolgende groeiseisoen gee aan die boer. Die apparaat kan ook die begin van die reënseisoen voorspel deur gebruik te maak van verskeie weer en klimaatsvoorspellings.