312
B. Lèye et al.
Fig. 1 Climatic zones of Burkina Faso (1981–2010). Source Agence Nationale de la Météorologie
du Burkina Faso
Fig. 2 Interannual evolution of the standardized rainfall index in Ouahigouya during the period
1961–2015
Figure 3 shows the evolution of the standardized precipitation indices at the
Ouahigouya station. There is great interannual variability in precipitation and drought
between 1969 and 1990, and between 1970 and 1994.
In the Sahel region, since the 1990s, there has been an average of four dry spells
per rainy season (Fig. 4a), which is higher than the previous period (1978–1990). A
dry spell is defined as a consecutive number of days without effective rainfall (i.e.,
a rainfall amount which is likely to trigger runoff) during the rainy season (Zouré
B. Lèye et al.
Fig. 1 Climatic zones of Burkina Faso (1981–2010). Source Agence Nationale de la Météorologie
du Burkina Faso
Fig. 2 Interannual evolution of the standardized rainfall index in Ouahigouya during the period
1961–2015
Figure 3 shows the evolution of the standardized precipitation indices at the
Ouahigouya station. There is great interannual variability in precipitation and drought
between 1969 and 1990, and between 1970 and 1994.
In the Sahel region, since the 1990s, there has been an average of four dry spells
per rainy season (Fig. 4a), which is higher than the previous period (1978–1990). A
dry spell is defined as a consecutive number of days without effective rainfall (i.e.,
a rainfall amount which is likely to trigger runoff) during the rainy season (Zouré