ASSESSMENT OF ONSET, CESSATION AND DROUGHT EVENTS FOR RAINFED WHEAT (TRITICUM AESTIVUM SSP.) PRODUCTION: THE CASE OF MISHA WOREDA, SNNPR, ETHIOPIA

Abstract

Agriculture in Ethiopia is heavily dependent on rainfall. However,the rainfall is highly varying spatially and temporally affecting cropping calendar and productivity. Drought has a great impact on agricultural, hydrological, economic,environmental and social systems.The existence of long dry spells has been the leading challenge of agricultural productivity and hydrological balance for decades in the country in general and southern region in particular. Therefore, assessment of rainfall characteristics and drought event in the southern regionof Ethiopia has got a special attention currently.This paper examined the onset and cessation dates of the rainy season over Misha woreda using rain gauge data from NMA over the period of 1987-2016. In addition, the inter annual variability of the onset and cessation dates for each climatic zone was assessed using Instat softwareversion 3.37.The onset and cessation dates were identified by using water balance techniques for two stations in Misha Woreda. To analyze the trend of rainfall, the widely used modified Mann-Kendall test was run at 5% significance level on time series data for each of the stations for the time period,1987to2016.The standardized precipitation index (SPI) was used to estimate drought events. According to the result, the average onset and cessation of rainfall were April 23 and October 30 at Fonko while April 14 and November 1 at Hosanna respectively. Different models like FAO (1978) and Reddy (1990) were used to analyze the onset, end and length of growing periods for ideal crop. Mean while, the growing periods were characterized for some selected crop,commonly grown in the study areas.Furthermore Markov Chain Model was used to assess the distribution of dry and wet spells inthe area.The result of crop water requirement of wheat showed that it doesn’t vary by planting date in the study area and the total water requirement ranged between 483.6 mm and 512.2 mm during the growing season.The assessment of different indices and using advanced tools, betterunderstanding and better response can be generated to mitigate the impacts. The results of analysis obtained both from the Markov Chain model and Reddy indicated higher probabilities of dry spell occurrences during Belg. Results of analysis of drought in the area revealed that during both Kiremt and Belg seasons relatively higher f requency occurrence of moderate drought event followed by severe drought event was found to occur at both stations and time scales except for some deviations. Moreover, both stations were found to experience all drought severity levels and respond differently to the 1, 3 and 6 month time scales in different manner. Since, dry events are found to be more probable than wet spell events for belg season so that for a given crop allocation of supplemental irrigation, particularly at critical growing stages is crucial and implementing water conservation measures such as mulching and other moisture conservation practices to reduce soil evaporation and conserve moisture in the soil is necessary as well.