Rising Lake Levels Across High Mountain Asia

Hassan, Javed; Nielsen, Karina; Colgan, William; Kayastha, Rijan Bhakta; Khadka, Mira; Khan, Shfaqat Abbas

doi:10.5194/egusphere-2026-808

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https://doi.org/10.5194/egusphere-2026-808

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02 Apr 2026

| 02 Apr 2026

Rising Lake Levels Across High Mountain Asia

Javed Hassan, Karina Nielsen, William Colgan, Rijan Bhakta Kayastha, Mira Khadka, and Shfaqat Abbas Khan

Abstract. High-altitude lakes across High Mountain Asia (HMA) are one of the critical freshwater reservoirs and sensitive indicators of climate change due to their remote locations and limited human disturbances. This study presents continuous water level estimates for 232 lakes across HMA from 2010 to 2024 using CryoSat-2 and ICESat-2 data. We analyzed temporal and spatial variations and inter-mission consistency in the lake water level across HMA. Our results reveal an overall increasing trend (median rate: +0.1 ± 0.01 m yr⁻¹), with 77 % of lakes experiencing rising levels and 91 % exhibiting statistically significant trends. We find a substantial regional heterogeneity with the Tibetan Plateau contributing dominantly to regional increase (0.07 ± 0.001 m yr⁻¹), while Himalayan lakes show persistent decline (0.04 ± 0.001 m yr⁻¹). Water level times series observed with the satellite altimetry missions CryoSat-2 and ICESat-2 intercomparison demonstrates strong consistency (80 % sign agreement, p = 0.013). Lake catchment scale analysis identifies precipitation as the dominant deriver of lakes water level variability (r = 0.42, p < 0.001), whereas lakes in glaciated catchments exhibit weak climate correlations despite significant increases in temperature, indicating nonlinear cryosphere buffering. We find systematic relationships between lake characteristics (area, elevation) and increasing water levels, with larger lakes generally showing more rapid growth. The contrasting hydrological responses with continued rising water levels in cryosphere influenced lakes and accelerating declines in precipitation sensitive lakes in Himalaya highlight divergent lake hydrological regimes. These findings underscore the critical importance of regional differentiation in understanding lake water storage changes and informing climate adaptation strategies for population vulnerable to these changes in the regions.

Received: 10 Feb 2026 – Discussion started: 02 Apr 2026

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Javed Hassan, Karina Nielsen, William Colgan, Rijan Bhakta Kayastha, Mira Khadka, and Shfaqat Abbas Khan

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RC1:
'Comment on egusphere-2026-808', Anonymous Referee #1, 25 May 2026
Reviewer comments on manuscript EGUsphere-2026-808 “Rising Lake Levels Across High Mountain Asia” by Hassan et al.
General comments:
This manuscript analyzes lake-level changes across 232 lakes in High Mountain Asia from 2010 to 2024 using CryoSat-2 and ICESat-2 data. The results show heterogeneous lake-level changes across HMA, with overall increases in the Tibetan Plateau lakes and declining tendencies in the Himalaya. The authors further examine correlations between lake-level changes and ERA5-Land precipitation, temperature, and evaporation to interpret possible hydroclimatic controls. While the dataset and regional synthesis are useful, the manuscript’s current scientific contribution is somewhat limited by a largely descriptive analytical framework. The conclusions regarding climatic drivers, cryospheric buffering, and regional mechanisms are not fully supported by the current analyses. The study would benefit from more robust attribution framework, and a more explicit statement of its novelty relative to previous HMA lake-level studies.
Specific comments:
About innovation. The broader finding on the rising lake-level in the central Tibetan Plateau and declining tendency in the southern Tibetan Plateau/Himalayan region is already well established in the literature. The authors state that the majority of previous studies are confined to the Tibetan Plateau. While, existing studies have either extended the analysis to high-elevation lakes above 2500 m a.s.l. (e.g., Zhang et al., 2020) or to glacial lakes across the entire HMA (e.g., Wang et al., 2025). It is useful that the manuscript extends the lake-level record to 2010–2024, however a 15-year period does not necessarily provide a clear advantage for assessing long-term trends. The manuscript should more explicitly state the knowledge gap, not only in terms of “more lakes and longer time series,” but new process understanding. For example, does the study reveal post-2018 acceleration or deceleration in lake-level changes? Or does it identify regional differences that were not captured by previous TP- or HMA-wide studies?

Wang Y, Zheng D, Zhang G, Carrivick JL, Bolch T, et al. (2025). Patterns and change rates of glacial lake water levels across High Mountain Asia. National Science Review, 12(3): nwaf041.
Zhang, G., Yao, T., Xie, H., Yang, K., Zhu, et al. (2020). Response of Tibetan Plateau lakes to climate change - Trends, patterns, and mechanisms. Earth Science Reviews, 208
About mechanistic interpretation. The manuscript relates lake-level trends to ERA5-Land temperature, precipitation, and evaporation trends. This provides a reasonable first-order analysis, but the Discussion often moves from correlation to mechanistic interpretation. For example, the authors suggest that lake expansion on the Tibetan Plateau is mainly associated with increased precipitation, that glacierized catchments reflect cryospheric buffering, and that declining Himalayan lakes indicate precipitation sensitivity and reduced meltwater buffering. These interpretations are plausible, but correlation analyses alone are not sufficient to infer dominant mechanisms. Lake-level change integrates catchment runoff, direct precipitation over the lake, evaporation, groundwater exchange, glacier and snow melt, and possible outlet dynamics. The authors should therefore either moderate the mechanistic language or strengthen the analysis, for example by introducing a simple lake water-balance framework to guide interpretation.

About uncertainty. The climate-driver analysis is based on ERA5-Land temperature, precipitation, and evaporation. Reanalysis data especially precipitation are highly uncertain in high-mountain regions, and this uncertainty directly affects the interpretation of correlations between climate variables and lake-level changes. The authors should discuss this limitation more explicitly. If possible, comparison with another precipitation product would strengthen the analysis.

About Discussion. The discussion of glacier melt and permafrost contribution mainly relies on previous studies. Some statements on glacier-melt buffering and permafrost-related contributions cannot be directed supported by the lake-level and climate-correlation analyses. The manuscript should make clearer which process interpretations are directly supported by this study and which are inferred from prior literature.

About regional classification. The manuscript groups lakes into Tibetan Plateau, Himalaya, western HMA, and glacierized catchments, however, the criteria are not described explicitly. In particular, “glacierized catchments” overlap spatially with the other regions. It is not clear whether these are treated as an independent category or a cross-cutting classification.

Given the above, I would recommend a major revision.
Citation: https://doi.org/10.5194/egusphere-2026-808-RC1
RC2: 'Comment on egusphere-2026-808', Anonymous Referee #2, 11 Jun 2026

General comments
This is an interesting submission using altimetry data to characterise changing lake levels across High Mountain Asia. It is well-structured and the methods appear to follow a well-established workflow. The findings are broadly consistent with previous regional studies, offering some new insights into spatial variability in lake-level trends. There are several aspects that I think could (should) be addressed before the manuscript is accepted; in particular the uncertainty quantification seems optimistic and the attribution of observed changes to climatic drivers rather simplistic (which needs acknowledging/discussing), and the framing of the work around 'glacial lakes' is somewhat misleading since they are not included in any of the analysis.
Specific comments
- The uncertainties calculated for each dataset look optimistic to me - there is some brief consideration, or acknowledgement, that the correlation errors are not accounted for, but how about accounting for things like the bias correction, given that a substantial number of the lakes show a different offset? How does this propagate into the presented trends? While the sign agreement of the trends derived by the two sensors is high, the rates of change (0.15 m/a-1 vs 0.052 m/a-1) are substantially different. How can this inconsistency be accounted for (and can some of that discussion/acknowledgement of the additional uncertainties that go beyond random noise - sensor mismatches for example) be included in the manuscript?

- The climate attribution is currently quite limited and probably overstated. The correlation between precipitation and lake levels is modest and only some of the subsets show significant relationships. As stated early in the manuscript these lakes integrate fluctuations in the contribution of meltwater, precipitation, permafrost thaw and groundwater so it's a complex picture, and probably doesn't conform to a linear relationship anyway. Even more so if you include storage effects and lags in meltwater routing for example. There should be a more extensive part to the discussion that acknowledges the different components of the water balance more directly and the fact that the analysis is limited by the resolution of the climate data and the absence of a lagged/multivariate/non-linear analysis.

- There are quite a number of citations within the manuscript that are not within the reference list - which on the face of it might seem to be a minor oversight but it makes it difficult for reviewers to properly evaluate how robust the argument being presented is (and therefore ultimately undermines the strength of this argument).

- Given that the study focuses solely on lakes of surface area > 20km2, all of the text about glacial lakes expanding (and becoming hazardous - with reference to GLOF events) seems somewhat redundant. I suggest those sentences in the introduction and the discussion should be removed.
Technical corrections (numbers refer to lines within the manuscript)
Is the title totally representative of what is presented, given that the abstract acknowledges heterogeneity across the TP and there is a decline in lake levels for the Himalaya?

21: declines should be presented as a negative number?

24: deriver = driver?

25: 'glacierised' here and throughout if you mean that the catchment currently has ice cover?

28: is growth the correct word here (and throughout)? This implies a lateral expansion to me, which your data do not assess. I suggest being consistent and using 'water level rise' instead.

40-45: this is an awkward sentence with too many parts to it. Can it be broken down a little bit? And checked for grammar too (lines 40-41 in particular)?

46: 'so understanding their...'

47: what is 'this' here - the antecedent is unclear

52: 'In the meantime' refers here to the previous studies of the previous sentence I think, but then it's specified as 'since 1990'. Maybe just delete the first three words to avoid any confusion/conflict.

Figure 1: I can't see lake I. Also where the labels are overlayed directly onto the lake circle they are difficult to make out. Also the caption states A-J, not A-I.

Figure 1: The placement of a (largely) results figure here in the introduction is a bit odd?

Section 2: how were multiple datapoints over each lake handled? Mean? Median? And which ERA-5 cell was selected for the climate analyses? (sorry if I missed these)

134-135: how were regulated lakes identified/derived?

138: correct the (R)

159: why is this 238 lakes?

160: is this systematic bias an average value? give the range if so? and why does it only apply to 77% of lakes?? What is the case for the other 23%!?

164: full-stop (not comma)

183: 179+54=233...?

Figure 2: I don't see any shading, as described in the caption

Figure 2: Is it possible to add the data points (in light grey for example) from which the relationships are derived?

Figure 2: The Himalaya combined line doesn't seem to be altered from the Cryosat one - is that real?

200-205: Couldn't this be a test for difference on a per-lake basis?

203-204: Might the reader see some numbers on how well the rates of change compare - in a scatterplot for example? Could all of the lake values be shown for the overlap period?

216-219: The total number of lakes here is significantly short of 232. why is that?

Figure 3: The splitting of the Cryosat data into two periods confused me for a bit here - is this introduced earlier in the manuscript or does an explanation need adding?

247: the start to this sentence is missing. 'The lakes in western HMA showed a consistent pattern, with 7 out of 12 experiencing...'?

266: On 'the' Tibetan Plateau...

Figure 4: These data look like they still have a seasonal signal to me...?

294: Lake catchments in 'the' Himalaya experience...?

Table 1 probably needs moving up as it includes important information about how many lakes are analysed per sensor per period (which accounts for some of my comments above)

lines 375-376: odd capital letters here

400: 'the' lake water budget. (full stop)

426: 'aligning'

425: I agree, but that's why they're large in the first place, so it doesn't account for why the relative rate of change is higher.

444-446: this study says nothing about glacial lakes and even less about GLOF hazards so I think this sentence can be removed.

473: citations should come after 'runoff' not 'presents'

Table S1: why are there 238 lakes here (232 referred to in the caption)?

Citation: https://doi.org/10.5194/egusphere-2026-808-RC2

Javed Hassan, Karina Nielsen, William Colgan, Rijan Bhakta Kayastha, Mira Khadka, and Shfaqat Abbas Khan

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https://doi.org/10.5194/egusphere-2026-808-supplement

Javed Hassan, Karina Nielsen, William Colgan, Rijan Bhakta Kayastha, Mira Khadka, and Shfaqat Abbas Khan

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Short summary

High-altitude lakes in High Mountain Asia (HMA) are important sources of freshwater and sensitive indicators of environmental change. Using satellite data from 2010 to 2024, we examine water level changes in 232 lakes across HMA. Results show rising lake levels on the Tibetan Plateau, while lakes in the Himalaya are declining. These contrasting patterns highlight strong regional differences and provide valuable information for understanding water availability and associated hazards.


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