Hydrological Model for Sustainable Development in the Aral Sea Region

Round 1

Reviewer 1 Report

This is a highly technical study involving some sophisticated mathematics in which I am not expert (e.g. differential calculus).  My sense is the authors are well versed in these methods and that their calculations and  modeling makes sense.  The study is interesting and novel in proposing to modify the hydrologic cycle in the Caspian/Aral region to increase regional precipitation by enhancing evaporation on a large-scale from existing water bodies and new water bodies to be created in the desert region between the Caspian and Aral Seas.  Their theory is predominant winds would carry moist air over the Aral sea Basin, increasing precipitation, and thereby raising inflow to the Aral.  Concerns I have about this approach are cost, complexity, and the effect on the Caspian Sea hydrology of diverting large amounts of  water to fill the lakes to be created in the desert between the seas.  The English is understandable but needs a fair amount of  improvement.

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript concerns the important issue of the water balance of the Aral Sea, which is undergoing the catastrophic consequences of the rapid level decrease observed from the middle of the last century to the present time. The manuscript attempts to offer a method for increasing the income component of the water balance of the Aral Sea. In addition, a long-term forecast of the lake water volume variability is calculated basing on the proposed scenarios.

The issue raised is important for the region of Central Asia, and is also important for other regions of the arid zone suffering from anthropogenic diversions of freshwater inflow.

However, for several reasons, current state of the manuscript does not allow to correctly assess the quality of the proposed calculations and the reliability of the obtained results, as well as to compare the results with other modern research.

The article does not have a clear structure. There are an introduction and conclusion sections, but the article does not have a section on "methods" and "results". It does not allow to estimate which part of the experiment is the author contribution, and which part is based on previous studies.

Introduction section mostly considers different aspects of the Aral Sea crisis and problems with water management in the Central Asia, while there are no literature review on water balance modelling and other studies of “natural evaporators” techniques together with “rainmaking technology” (do they exist? -  we can not understand it from the manuscript). Reading the Introduction does not allow to find out the world experience in using the methods proposed in the manuscript. Moreover, there is no strong literature review on the Aral Sea water balance modelling, while there are numbers of studies considered this important question.

Central idea of the manuscript is the connection between the Aral Sea water balance and the Caspian Sea basin. Part of the Caspian Sea, the Kara-Bogaz-Gol, can be considered as the “natural evaporator” providing the increase of income component of the Aral Sea water balance through the precipitation. These two isolated from each other endorheic basins have the connection only through the regional atmospheric patterns, which are briefly discussed, average annual directions are determined. Meanwhile, to calculate the real amount of precipitation, that originated from the Caspian Sea and influenced the Aral Sea water balance, some physically-based approach should be implemented. Instead, some correction coefficient was used: line 211 “rC is the correction coefficient (0.065) reflecting the role of Caspian Sea in the water balance of the Aral Sea”. What is the scientific base for this value?

The other important issue is that the during the desiccation the Aral Sea divided into the several separated water bodies with different geographical and hydrological conditions, that implies significant differences in water balance conditions between these basins. Separation of the Small Aral Sea from the main part occurs in the late 1980s. Furthermore, the Large Aral Sea divided into two basins (eastern and western). Then, the manmade dam Kokaral was built to recover the Small Aral in 2005. All of these and many other events resulted in forming of different regime of water balance between the basins of the former Aral Sea, however, authors did not mentioned these important facts in the manuscript. Equations of water balance should be considered for each basin separately. If the water balance of the entire system is considered, the corresponding assumptions should be made and discussed.

Quite often, there are no references to values of the used parameters, such as evaporation and precipitation rates etc. Some examples are given below in specific comments.

Several issues concerning the simulations:

1) The way of calculation of the Aral Sea morphological parameters such as volume and surface area is not clearly shown.

2) Temporal scale t=1 day (line 258) used in the simulation experiment needs available time series of all considered components of water balance with the same temporal resolution. However, any mentions of these data are missed in the text.

Thus, I would recommend to reconsider the structure of the article making clearly divided sections, such as Introduction, Methods, Results, Discussion and Conclusion. Introduction section should be focus on detailed and wide review of the recent studies on similar scientific problem. In the Methods section experiment design should be described more accurate, as well as the initial conditions of the simulations, data used etc. The manuscript could not be published in the current form.

English language needs significant improvement; verbs, articles and even words are missed in the text from time to time.

Specific comments:

Lines 44-47: What is the base for these statements? References or additional explanations needed.

Lines 87-89: References for the values of water balance components needed

Lines 104-105: "the Aral Sea water balance significantly depends on the Caspian Sea" - this statement is not obvious and has to be supported by previous studies or additional explanations.

Line 118, Table 1: “Hydrological history of some components of the Aral Sea Basin is shown in 89 Table 1 (Gaybullaev et al., 2012; Micklin, 2016; Breckle and Geldyeva, 2012).” – the latest reference is from 2016, while “some components of the Aral Sea Basin” are also shown for 2018 in the Table 1. What is the source for data of 2018?

Line 321-322: “The salinity of the Aral Sea 321 increased from 10 g/l to 135g/l” What is the source for these values? Apparently, salinity of the Large Aral is considered. As it was already shown above, the Aral Sea has several basins with different values of salinity. For example, salinity of the present-day Small Aral Sea is close to the pre-desiccation state (10-11 ppt).

Decimal delimiter for numbers should be unified throughout the manuscript.

Author Response

Please see the attachment

Author Response File: Author Response.pdf