Spatial variability and distribution of main rainy season onset, cessation and growing length at tekeze river basin, Ethiopia

Main rainy season onset, cessation and growing length are not the same for the entire Tekeze river basin. Knowledge on onset, cessation and growing length of the main rainy season in the river basin is very important for various decision making activities such as agricultural activities for sowing and harvesting, in optimum utilization of limited resources including water, labor and fertilizer, for efficient irrigation water utilization, for interpreting a given seasonal forecast and for drought risk identification and assessment. This study examined the spatial variability and distribution of Kiremt (June to September) season onset, cessation and growing length over Tekeze river basin, Ethiopia. Daily rainfall data were used over the basin based on data available from 23 meteorological stations. Data quality control was done for infilling missing values and main quality tests of outliers and homogeneity tests. Spatial distribution and variability were investigated using ordinary kirging interpolation technique. The results showed that: (1) The Kiremt onset (start of main rainy season) begins earlier in the west part of the Tekeze river basin and is distributed slowly to central and east parts of the basin; (2) Kiremt cessation (end of the main rainy season) is late in the south and west part of the river basin than the other parts; (3) Kiremt growing length which is the difference between Kiremt cessation and Kiremt onset is high over south and west part of the basin and is low over northeast part of the basin. Higher growing length over south part of the basin is due to late kiremt cessation over the area and high growing length over the west part of the basin is due to early kiremt onset and late kiremt cessation over the area. The reason of low kiremt growing length in the northeast part of the basin is due to late kiremt onset and early kiremt cessation over the area; (4) The spatial variability of kiremt onset is higher than the spatial variability of kiremt cessation especially in the east part of the river basin.