In the sudan savanna of northern Nigeria, with its semi-arid climate, the ability to determine effectively or predict the start of actual productive rains cannot be overemphasized. Several methods exist for calculating the date of onset of the rains that may be taken as the start of the growing season. Five methods currently in use, which are relatively easy to apply on a large scale, were selected for comparison. One is a traditional technique (Ramadan method), two use accumulated rainfall totals (Walter's and Sivakumar's methods), and two use rainfall-evapotranspiration relationships (Kowal's and Benoit's methods). For the period 1961-91, the traditional technique performed most poorly. Walter's method gave quite early onsets and Sivakumar's method gave very late onsets, thereby seriously shortening the growing season. Kowal's and Benoit's determinations fell most often in between the results of Walter's and Sivakumar's methods in their performance. However, although generally to a lesser extent than the other methods, they are still significantly affected by false starts. To avoid incorrectly predicting the growing season's onset as far as possible, but to prevent an unacceptable shortening of the growing season, a combination of Kowal's and Sivakumar's criteria was used to develop an improved technique. This proved to work well for determining the onset date in the study area. However, because some false starts remain when using average onset dates, it is suggested that an operational advisory team should be constituted by the government. This team would be responsible for calculating onset dates in any year, on-line for the ongoing season, in a participatory approach with farmers, and for disseminating such dates to the farmers. This could be done for any place for which the appropriate data can be made available. In the future, improved climate prediction skill may replace the classical probabilistic approaches presently suffering from increasing rainfall variabilities.

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Abstract. In agrometeorology and management of meteorology related natural resources, many traditional methods and indigenous technologies are still in use or being revived for managing low external inputs sustainable agriculture (LEISA) under conditions of climate variability. This paper starts with the introduction of an "end-to-end" climate information build up and transfer system in agrometeorology, in which the use of such methods and technologies must be seen to operate. It then reviews the options that LEISA farmers have in risk management of agrometeorological and agroclimatological calamities. This is based on the role that the pertinent meteorological/climatological parameters and phenomena play as limiting factors in agricultural production and the expectations on their variability. Subsequently, local case studies are given as examples of preparedness strategies to cope with i). variable water/moisture flows, including mechanical impacts of rain and/or hail, ii). variable temperature and heat flows, including fires, and iii). fitting cropping periods to the varying seasons, everywhere including related phenomena as appropriate. The paper ends with a series of important additional considerations without which the indicated strategies cannot be successful on a larger scale and in the long run.

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