On determining the ‘real’ onset date of seasonal rains in the semi-arid and sub-humid areas of West Africa

An experiment in intra‐seasonal agricultural drought monitoring and early warning in the Sudano‐Sahelian Belt of Nigeria

“…AGRHYMET () used daily or decadal rainfall, potential evapotranspiration and soil water holding capacity above the wilting point, to give EW indicators of crop water balance. Another study, by Usman and Abdulkadir () also showed similar possibilities with respect to the 1970–1999 rainfall over Minna and Kano.…”

“…This study proposes a simple drought monitoring and EW methodology hinged on an Intra‐seasonal Rainfall Monitoring Index (IRMI) developed by Usman and Abdulkadir () as a tool for determining the real onset date of the summer monsoon rains. IRMI is computed on a pentad by pentad basis from the beginning of May using the expression, (Cpt) 2 /(hpt × Nb × 100), where Cpt is cumulative pentad rainfall since May 1, hpt is the highest pentad total rainfall since May 1, Nb is number of breaks in rainfall (pentads with less than 5 mm of rainfall) and 100 is a factor.…”

“…This way, the index rises gradually as the rains become steady and then falls as the rains cease. See Usman and Abdulkadir () for additional details. Consequently, IRMI is capable of determining the actual pentads of effective onset and cessation of the rains at the individual farm level with the simplest of daily rainfall records, a very clear superiority over the probabilistic seasonal onset forecasts that currently dominate agricultural decision‐making across the country.…”

“…The premise is that IRMI is computed on a pentad by pentad basis and its value of each pentad is a measure of the amount and spread of rain received and thus a good indication of the moisture situation. By inference, the presence or otherwise of agricultural drought, (Usman and Abdulkadir, ), the beginning (or onset) of drought and its corresponding intensity can be determined and its development monitored as the season progresses. A classification proposed in this regard is that classes 1 and 2 are indicative of abundant and adequate moisture conditions whereas classes 3, 4 and 5 are indicative of deficient, very deficient and extremely deficient moisture conditions as presented in Table .…”

Characterization of Monsoonal Rainfall in the Sudano-Sahelian Zone of Northwestern Nigeria

“…Water balance models have been extensively built and employed in determining RODs and RCDs by scholars (Kowal & Knabe, 1972;Walter, 1967;Fasheun, 1983;Samba, 1998;Omotosho et al, 2000;Ati et al, 2002;AGRHYMET, 2005;Usman & Abdulkadir, 2012). We can deduct from these works that, for sure, RODs and RCDs differ from place to place and they can be measured using varieties of quantitative analytical frameworks ranging from simple to complex mathematical equations.…”