peer review report 2 on comparing trends in hydrometeorological average and extreme data sets around the world at different time scales

Journal of Hydrology: Regional Studies 9 (2017) 29–30

Contents lists available at ScienceDirect

Journal of Hydrology: Regional
Studies
journal homepage: www.elsevier.com/locate/ejrh

Peer review report 2 on “Comparing trends in hydrometeorological
average and extreme data sets around the world at different time
scales”

1. Original Submission
1.1. Recommendation
Major Revision
2. Comments to Author:
Review
This work proposes an extensive analysis of trends in hydrometeorological data worldwide. This topic has been the
subject of many papers since the growing concern over climate change, but most of them were geographically limited to one
region. The authors review them thoroughly. The paper proposes no methodological advancement and ignores (on purpose)
the issue of the influence of the autocorrelation of the data on the Mann-Kendall trend test results.
Comments
The topic addressed by this paper is quite simple and has been already addressed by many authors. The document is thus
in general an easy read, since most results and methodologies can be anticipated.
The authors have done a good job of reviewing the abundant literature on this topic.
Line 169: with up to 20% missing data, not all random variables contain 41 values. Could that be documented somehow?
For instance, what is the distribution of the length of the random variables?
Figure. 2 is not informative and should be removed. In fact it took me some time to understand that there is no particular
reason beside succinctness for the authors to have left out some months and years.
Section 2.4 is very disappointing. One cannot just write we are doing the same as Morin (2011) and go on. I was at
least expecting some information on how the authors have proceeded to eliminate the adverse effect of autocorrelation on

the results of their trend tests. I finally found that information about 150 lines later. 1) The authors should include their
comments from lines 352 to 364 in Section 2.4. 2) The authors have not convinced me that the issue of autocorrelation is
too hard to address and could be neglected (line 364). They should consider the paper from Hamed (2009. Enhancing the
effectiveness of prewhitening in trend analysis of hydrologic data. Journal of Hydrology 368, 143–155) that proposes an easy
to be applied solution to this problem. 3) If the authors persist in not accounting for autocorrelation, they should make a
better case about it in Section 2.4 before exploring the results.
Section 2.4 is also silent about the methodology used to calculate the trends. Most authors nowadays opt for a Theil-Sen
approach. Is it the case?
Lines 247–249 are misleading. The general message should be that precipitation show no trend in both hemispheres. I
propose to remove lines 247–249 as well as Figure 3(what is the interest of some isolated trends on the global picture?).

DOI of the original article: />2214-5818/$ – see front matter
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Peer review report 2 on “Comparing trends in hydrometeorological average and extreme data sets around the world at different time scales” / Journal of Hydrology: Regional Studies 9 (
30

Figure 6 is misleading because one may think that there no trends in Africa, Europe and Asia, while the absence of trends
reflects the absence of data, as drawn in Figure 1c. The authors should consider removing Figure 6 or at least add a note to
warn readers.
Figure 7 is difficult to read and should be reworked.
Up to line 402, the paper was very factual and no hydrometeorological interpretation of the trends were provided. I was
thus surprised to read some interpretations, for discharge only, in the conclusion from lines 402 to 407. The authors have
two options: remove lines 402–407 or provide physical interpretation for all variables (and much earlier in the document
than in the conclusion).
Lines 41–418 are a bit puzzling located in the last paragraph of the conclusion. This issue should have been raised in the
methodology (Section 2.4), if at all.
Anonymous