Abstract
The ever increasing population and consequently increase in demand for food and the increasing exploitation of the land justifies the need for adequate studies on rainfall as an important factor affecting agricultural production. The date of the onset of rains is an important factor in planning agricultural operations such as land preparation and sowing. The study conducted agro-statistical analysis of rainfall characteristics over three different zones of Nigeria. Daily rainfall data were collected for the period between 1971 and 2005 for 6 stations and were subjected to standard analysis to determine trends and variations in the onset dates, cessation dates, length of rainy season, number of wet days, drought episodes. The results showed that the inter-annual variability of the onset dates is higher than that of cessation dates with a progressive shift in both onset and cessation dates. The length of rainy season varied from 77-291 days in Guinea zone, 77-243 days for Savannah and 73-155 days for the Sahel. Changes in the length of growing season ranged between -9 and -10 for Guinea zone, -21 and 11 days for Savannah zone and -28 and 20 days for the Sahel. Similarly, the numbers of wet days have declined over Nigeria. The information presented in this study are to serve as input for proper land and water resources management for productive agricultural enterprise across the three major agro-ecological zones of Nigeria.
Highlights
Knowledge of trends and variations of current and historical hydro-climatological variables is pertinent to the future development and sustainable management of water resources of a given region especially within the context of global warming
Enugu ranges from 77 days to 215 days and the number of dry days (NDD) in Enugu ranges from 221 days to 290 days while the number of wet days (NWD) ranges from 75 days to 144 days
The onset of rain in Ondo ranges from 9th of February (68 DOY) to 1st of May (121 DOY) as shown in Table 2, while the earliest cessation date in Ondo was 28th of September (271 DOY)
Summary
Knowledge of trends and variations of current and historical hydro-climatological variables is pertinent to the future development and sustainable management of water resources of a given region especially within the context of global warming. One of the very important necessities of research into climate change (Houghton et al, 1996) is to analyze and detect historical changes in the climatic system. Rainfall is a principle element of the hydrological cycle, so that understanding its behavior maybe profound social and economic significance. The detection of trends and oscillations in precipitation time series yields important information for the understanding of climate. Several studies have been carried out on different temporal scales and in different parts of the globe. Existing analysis of daily series, show for some areas a positive trend in daily precipitation intensity and a tendency toward higher frequencies of heavy and extreme rainfall in the last few decades (Houghton et al, 1996). Many authors analyzed the precipitation pattern in several parts of Europe.
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