Assessment of the severity and impact of drought spells on rainfed cereals in Morocco

Drought is a major factor affecting cereal production in most the rainfed areas of West
Asia and North Africa. Recent increases in drought frequency in Morocco have resulted in
the yields of field crops being extremely variable and generally low. The objective of this
study is to assess drought severity in the main cereal production areas of Morocco and to
evaluate its effects on grain yield. Also the study seeks to evaluate if the standardized
precipitation index (SPI) may be used as a tool to predict drought and crop yield early in
the season. Data analysis showed that for the period 1988 to 2008, yields fluctuated from
150 to 3000 kg/ha with a coefficient of variation of between 30 and 50% in the north and
60 and 70% in the south. Based on the SPI, the regions studied experienced, on average,
a drought once every 2.6 years. However, very severe droughts were observed only once in 7 years. The SPIs computed for the periods October to June and January to March were
highly correlated. Moreover, there was a high positive correlation between the yield and
the SPI calculated for the period January to March. The coefficients of determination
varied between around 0.20 and 0.62 for bread and durum wheats, and between 0.28 and
0.69 for barley. It is concluded that soil moisture levels during the tillering and stem
elongation periods of the cereals are the most important determinants of yield. Hence an
SPI computed for the period January to March can be used to predict drought severity and
yields early in the season