Determination of onset, cessation of rains and hydrological growing season in Dadin Kowa and Gombe for agricultural planning
This study determined the onset, cessation of rains and length growing season (HGS) in the Sahel Sudan of northeastern Nigeria. Two stations were selected for the study; Gombe town in Gombe LGA and Dadin Kowa in Yamaltu Deba LGA of Gombe State. Daily rainfall data was obtained from NIMETS and Upper Benue River Basin, Dadin Kowa, Gombe State. The rainfall cumulative model was adopted for this study. The first step of the method was to derive the daily rainfall that occured at each five-day interval in a year. A rainy day in this study is a day with zero point two five millimeters that occured within twenty-four hours. This is followed by computing the total of the five-day period. Finally, when the cumulative rainfall total is plotted against time through the year, the first point of maximum positive curvature on the graph corresponds to the time of rainfall onset, while the last point of maximum negative curvature corresponds to rainfall cessation. The difference between the onset and cessation in days is hydrological growing season (LGS). Result shows that onset dates for Gombe town and Dadin Kowa are 25 and 30 May, with a variability of +10 and +15 days, respectively. While cessation dates, is 12 October, for Gombe town and Dadin Kowa with a variability of + 10 days. The hydrological growing seasons is 140 days with a variability of + 10 days for Gombe town and 137 days with a variability of + 15 days for Dadin Kowa. A radar diagram was used to compare onset, cessation and length of growing season in the two locations temporally from 2001 to 2017. Results revealed that onset and length of growing season followed same trend with Gombe town having the dominant late onset while Dadin Kowa had the longest length of rainy season between 2001 and 2017. In terms of cessation from 2001 to 2017, Dadin Kowa on the average had late cessation. The results of this study would be useful to farmers and other stakeholders in planning agricultural calendars.
Keywords: Onset, Cessation, Hydrological Growing Season (HGS) and radar diagram