DETERMINING THE ONSET AND CESSATION OF SEASONAL RAINS IN SHIRE VALLEY, SOUTHERN MALAWI

Agricultural activities in Malawi depend largely on rainfall-fed. Rainfall onset is defined as the period, at the beginning of the rainy season, when rainfall distribution has become adequate for crop development while rainfall cessation refers to the period, towards the end of the rainy season, when rainfall distribution may no longer sustain crop growth. Malawi has a tropical savannah climate with distinct rainy season from November to April during which 95% of the seasonal precipitation takes place and dry seasons from May to October, however from May to July it is relatively cool and in some high altitude areas drizzles (chiperoni rains) are common. This study determined the onset and cessation of seasonal rains in shire valley, southern Malawi, with the objectives of characterizing the rainfall variables for seasonal rains in Shire Valley, southern Malawi from 1990 to 2019, analyzing the trends in the onset, cessation and length of rainy season and classifying onset and cessation dates. Daily rainfall data from 1990-2019 were obtained from the Department of Climate Change and Meteorological services. The onset and cessation dates were generated by using R-Instat. The summary of the averages of onset dates and cessation dates shows that rainfall first occur in Nsanje on 28 November followed by Ngabu on 7 December then Nchalo on 9 December. The cessation date of rainfall is almost the same in all stations with Nchalo and Ngabu on 3 April while Nsanje has its cessation date as 5 April. It has been noted that the majority of the years lie within the normal category however some years are observed to have early or late onset which could be linked to global interconnections e.g. Lanina or El-Niño. The Mann-Kendall analysis, it shows that Ngabu and Nsanje has an increasing trend that indicates a delayed start of rains but insignificantly while Nchalo shows a decrease in trend which means that there is early onset in the station. The onset dates have shifted but insignificantly. There is an increase in trend in the cessation for the three stations which means that there is late withdraw of rains. Ngabu and Nchalo show an increasing trend in the length of the growing season while Nsanje shows a decreasing trend in the length of the growing season. These findings would therefore contribute significantly to the effective management and sustainable development of the national and district social economic activities.

Rainfall onset is defined as the period, at the beginning of the rainy season, when rainfall distribution has become adequate for crop development while rainfall cessation refers to the period, towards the end of the rainy season, when rainfall distribution may no longer sustain crop growth. Malawi has a tropical savannah climate with distinct rainy season from November to April during which 95% of the seasonal precipitation takes place and dry seasons from May to October, however from May to July it is relatively cool and in some high altitude areas drizzles (chiperoni rains) are common. This study determined the onset and cessation of seasonal rains in shire valley, southern Malawi, with the objectives of characterizing the rainfall variables for seasonal rains in Shire Valley, southern Malawi from 1990 to 2019, analyzing the trends in the onset, cessation and length of rainy season and classifying onset and cessation dates. The Mann-Kendall analysis, it shows that Ngabu and Nsanje has an increasing trend that indicates a delayed start of rains but insignificantly while Nchalo shows a decrease in trend which means that there is early onset in the station.

The study was conducted in shire valley, southern Malawi. It constitutes district such as: Chikwawa, Mangochi, Nsanje, Balaka and Machinga this is according to Department of Climate Change and Meteorological Services categorization. The shire valley is located in south western Malawi and extends into Mozambique as part of the Great Rift Valley systems of Africa. It covers an area of some 250, 000 ha in the two administrative districts such as Chikwawa and Nsanje. The valley has an elongated plain with a width of between 8 to 40km and lies altitudes of between 30 and 150m above seas level (Phiri & Saka, 2008). According to Vanya (2012) also said to that variability in climate associated with increased weather extremes resulted in shifts of rainfall onset dates, reducing crop growing period.

Traditional authority: TA Makhwira

District: Chikwawa

Coordinates: -16.2776, 35.0011