From pointwise testing to a regional vision: An integrated statistical approach to detect nonstationarity in extreme daily rainfall. Application to the Sahelian region

Abstract

[1] Global warming is expected to intensify the hydrologic cycle. Documenting whether significant changes in the extreme precipitation regimes have already happened is consequently one of the challenging topics in climatic research. The high natural variability of extreme precipitation often prevents from obtaining significant results when testing changes in the empirical distribution of extreme rainfall at regional scale. A regional integrated approach is proposed here as one possible answer to this complex methodological problem. Three methods are combined in order to detect regionally significant trends and/or breakpoints in series of annual maximum daily rainfall: (1) individual stationarity tests applied to the raw point series of maxima, (2) a maximum likelihood testing of time-dependent generalized extreme value (GEV) distributions fitted to these series, and (3) a heuristic testing of a regional time-dependent GEV distribution. This approach is applied to a set of 126 daily rain gauges covering the Sahel over the period . It is found that only a few stations are tested as nonstationary when applying classical tests on the raw series, while the two GEV-based models converge to show that the extreme rainfall series indeed underwent a negative breakpoint around 1970. The study evidences the limits of the widely used classical stationarity tests to detect trends in noisy series affected by sampling uncertainties, while using a parametric space and time-dependent GEV efficiently reduces this effect. Showing that the great Sahelian drought was accompanied by a significant decrease of extreme rainfall events is the other main result of this study.

Trend in the Co‐Occurrence of Extreme Daily Rainfall in West Africa Since 1950

“…In the central Sahel, the stationary levels have barely been recovered so far. These results on extreme rainfall evolution in the central Sahel are coherent with Panthou et al () who found a significant decrease of around 10% in the 2 year return level of the periods 1950–1969 and 1970–1990. Over the recent decade, the evolution of the K ‐year return level in the central Sahel is also in line with the upward trend in daily rainfall maxima shown by Panthou et al ().…”

“…A change in the 1980s is found with a period of decreasing rainfall intensity between the 1950s and the 1970s, followed by a period of increasing intensity since the 1980s. This confirms previous results found for the central Sahel by Panthou et al () and Panthou et al (). It is also in line with the increasing trend in extreme rainfall detected since 1982 by Taylor et al () over the entire Sahel.…”

Modeling non-stationarity in intensity, duration and frequency of extreme rainfall over India

“…A regional trend detection technique (Panthou et al, 2013) can be employed to improve the signal to noise ratio in a future study. Also, other physical covariates can be considered to study the changes in extreme rainfall characteristics.…”

Characterising the space–time structure of rainfall in the Sahel with a view to estimating IDAF curves

“…3. Table 1 obtained for a much larger area in this region by Panthou et al (2012Panthou et al ( , 2013, working on the data of 126 daily rain gauges covering the period . Note also that the temporal scale exponent (η) is large (0.9), which means that the intensity strongly decreases as the duration increases.…”