The manuscript is overall quite clear and well written. Giving more details about the novelty of the (quantitative) approach compared to the existing literature (indicated as rather qualitative) would highlight the significance of this work.

Below are list of items requiring some clarification and some suggestions.



Abstract

Line 10: what do you mean by ‘groundwater droughts and floods’? Droughts and floods refer to surface phenomenon. Do you mean the impact of drought and flood variability on groundwater levels?

Lines 19 to 22: missing verb or part of the sentence, reformulate.

Introduction

Line 55: it would be interesting to recall briefly the definitions of the other type of draughts and highlight how they are linked to each other or at least to the GW draught.

Line 65-66: this sentence is not clear. Can you reformulate?

Effective precipitation and groundwater data

Lines 183 to 185: I do not understand what is meant by mesh or SAFRAN mesh (temporal, spatial, spatio-temporal), and to which aim it will be used (to model which process or quantity of interest?). What is SAFRAN?

Section 3.1

An illustration of the variability or energy level of the MODWT approximation might be insightful, e.g on fig 2a.

Would a graphical or table presentation of the MODWT and CWT results help in understanding how the variability is quantified?

Section 3.2

Are the 0.2 and 0.8 percentiles unique/determined for the whole dataset or by aquifer group or borehole, and over which time period?

Multi-timescale variability…

Fig. 3: it might be good to recall that the energy level is a result from the MODWT.

Fig.4 caption: explain what the contour lines mean

For fig 5, 6, 10 & 11 it might facilitate the reading of the results if there was an identification of the hyrdogeol entity types (iD, iMD, cAM, cA) instead of displaying the coloured hydrogeological entities.

Discussion

Could you discuss the possibility of assessing the current LFV state and its short term evolution, given a type of aquifer, as it might be helpful for short term predictions of GWE ?

This work investigates the effect of low-frequency variability on low and high

groundwater levels extremes measured in the Paris basin. To my understandin,

all methods have been applied correctly and lead to resuts which allow a

thorough analysis of the "low-frequency variability induced extremes".

I have some minor questions and remarks.

L11 - At first reading it is not very clear what is meant by "sensitive". Maybe

use "low GWLs are stemming/resulting from such low-frequency..".

L16 - consisted in

L41 - I would say "in the context of global change"

L42 - for our societies.

L50 - Hydrological droughts

L56 - " et rates, that cause low soil moisture content.. " I am not too familiar

with this, but here I do not see a difference of gw droughts compared to

hydrological droughts.

L65 - according to the type of aquifer and GWL variation.

L69 - I would say that a water level higher than the soil surface is no

groundwater anymore.

L86 - "However, although these indices are useful tools to describe droughts,

their principal limit arises from the standardisation allowing for spatial

comparison but therefore hindering to keep the variance notion in time

series" You are stating important facts here, but especially the second part is

difficult to follow. I suggest to split the sentence in 2 and explain better

what you mean.

L89 - dependent on

L107 - .. highlighted, using a composite analysis with Sea Level Pressure (SLP),

that the.. (comma insertions)

L119 - I don't understand. Please rephrase.

L122 - except the 1975 drought.

L126 - delete "to", replace "in supporting" with "on"

L132 - high- and low-freuquency

L134 - Why exaclty where these 7 and 17 year variabilies chosen? I think this

needs explaining.

.. consists in evaluating

140 - Rephrase please

L145 - Boreholes were selected from a BRGM database and were required to be

undisturbed from human acitivites. We selected the boreholes by following the

three steps below.

L149 - the removal of pre-selected..

L170 - Do you mean sub-monthly?

L190 - were -> was

L214 - for that purpose

L245 - But isn't this also a consequence of the initial amplitude of exceedance?

Fig3 - I prefer the term variance, but this is a matter of preference.

Fig9 - Why not splitting the period exactly in half, doing the analsis for both

periods and the complete period 1903-2019?

P23 - 28 : I wonder how the results are sensitve to the choice of 7/17 and 7&17

year variablilty. I think this has to be discussed or at least commented on.

L582 - typo

L584 - linked to -> resulting from

L589 - dating back to

L595 - Which aperiodic behaviour? I don't understand this sentence

L601 - largely -> generally