Rainfall data come from the service of the Agency’s documentation for the Safety of Air Navigation in Africa and Madagascar (ASCENA) at the airport of Bertoua and the National Meteorology of Cameroon. They are recorded from 5 rainfall stations distributed over the basin and whose observations sizes vary from one station to another. The Longest chronicle (1969-2014) is recorded in the rainfall station in Bertoua, located in the North East of the basin. This long series will better appreciate the long-term rainfall variability.

Hydrometrics data are from the 1972-2013 period stations Bertoua and Batouri, extracted from the database of the hydrological research centre of Cameroon and field descents.

Changing rainfall indices between 1960 and 2012 suggests three possible ruptures. Before the first break that marks the end of the 1960s, there have been positive rainfall indices. This is typical annual rainfall above the average interannual due to an excess rainfall regime during this period. For the 1970-1992 sequence, almost 90% of the years concerned correspond to negative rainfall and hydrometric index reflecting a deficit rainfall pattern (Figure 2). A return to surplus occurs years after this deficit sequence in deficit until 2000. The decade 2010 is not yet complete, is characterized by alternating positive and negative indices. Subsequent monitoring of the rest of the series will better identify the trend of this decade.

In deciding on the number of disruptions in rainfall to retain, the application of tests and Lee Heghinian, Pettitt (Table 2) have permited to detect a single break in 1969 while the segmentation Hubert has detected one in

1969 and another in 1992 in line with the indices previously observed. Ndam et al. (2016) in their study of the Sanaga and Mfochivé (2011) on the catchment area of So'o, observed rainfall ruptures between the years 1968 and 1970. This is also the case Kpoumié and al. (2009) on the Sangha basin. This breakdown shows that the catchment area of Kadey fits well in general changes in rainfall patterns observed in the late 1960s in Central Africa in general and in the Congo Basin in particular.

Breaks tests applied to hydrometric data (Table 2) confirmed a single break on the two observed from rainfall indices. That of Lee and Heghinian detected a break in 1988 while those of Pettitt and Hubert confirmed that of 1992. After the breaks as well as gauging rainfall observed in 1969 by Lebel and Vischel (2005); Servat et al. (1995); Goula et al. (2006) and by Mahe et al. (2000) in 1991, the 1988 break seems specific to data quality and tests used. On three tests applied, that of Lee and Heghinian is the only to detect.

The annual rainfall totals are, in general, the more important they are rare (Figure 3). So we can see that before the break of 1970, annual rainfall less than 1350 mm showed a recurrence of at least 1 time every 5 years (Figure 3(a)). Beyond this value, precisely from 1420 mm, annual totals have long return periods (20 years) to very long (100 years). During the period 1970-1992, for the same return periods, annual rainfall has significantly decreased accumulation (Figure 3(b)). This is the case when there is a return of 3-year period before 1970. At this level, the cumulative rainfall of 1300 mm became centennial.

In short, we can say that the climate change that has occurred during the 1970s has had the impact of a variation of the recurrence of rainfall annually until 1992 on the whole basin. However, at the beginning of the 90s and especially after 1992, it is noted that the recurrence of annual rainfall has shifted to the behavior observed during the decade 60 (Figure 3(c)). This new trend reflects a rainfall recovery that seems to break the long “drought” highlighted by many authors [20] [22] - [25] .

1) SPI and ranges of values meaning

Fluctuating hydro data observed on the Kadey basin materialized by alternating wet and dry years as shown by the evolution of SPI indices. In this way, on the basis of these indices expressed by rainfall data for the study period (1960-2013), 25% of years of observation have suffered a moderate drought and only 11% correspond to a severe drought plan. In contrast, we note that over the same period, 47% of years running under a moderate moisture regime and the remaining 17% correspond to a moisture content ranging from high to extreme (Table 3). On the pelvis, SPI expressed from flows are characteristic of a “drought” (42%) from high (15%) to moderate (27%). The 58% of the remaining years undergoes moisture to varying degrees (Table 3).

Out of all the two hydroclimatical parameters, the “drought” has a generally moderate nature. However, a considerable number of years have suffered very heavy periods “drought”, this number also appears higher for the flow.

2) Deficit (or excess) rainfall and hydrometric

Observations, we note: before 1970, the average annual rainfall is 1477 mm. It increased to 1 268 mm between 1970 and 1992. This corresponds to a deficit of about 14% which is in the same range as that observed elsewhere in the other basins in South Cameroon [26] - [30] . After 1992, the trend has shifted to an excess of about 18, 5% until 2008 and 20% in 2012. In contrast to rainfall, hydrometric series is truncated because it starts in 1972 and ends more or less between 2004 and 2005.

A break is observed in 1990 by the test Lee, but this is not confirmed by the two other rather that hold 1992 agreement with the rainfall. This rupture generated a gain of over 108% runoff. We can therefore infer that excess rainfall for 18, 5% - 20% or about 19%, you get a 108% surge in flows is 5, 5 times the rainfall surplus (Table 4). Everything resulting nonlinearity between rain and flow in the watershed Kadey as is the case in Equatorial area general and Southern Cameroon in particular [29] - [31] .