the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Downscaling precipitation over High Mountain Asia using Multi-Fidelity Gaussian Processes: Improved estimates from ERA5
Abstract. The rivers of High Mountain Asia provide freshwater to around 2 billion people. However, precipitation, the main driver of river flow, is still poorly understood due to limited direct measurements in this area. Existing tools to interpolate these measurements or downscale and bias-correct precipitation models have several limitations. To overcome these challenges, this paper uses a probabilistic machine learning approach called Multi-Fidelity Gaussian Processes (MFGPs) to downscale ERA5 climate reanalysis. The method is first validated by downscaling ERA5 precipitation data over data-rich Europe and then data-sparse Upper Beas and Sutlej River Basins in the Himalayas. We find that MFGPs are simpler to implement and more applicable to smaller datasets than other state-of-the-art machine learning models. MFGPs are also able to quantify and narrow the uncertainty associated with the precipitation estimates, which is especially needed over ungauged areas, and can be used to estimate the likelihood of extreme events that lead to floods or droughts. Over the Upper Beas and Sutlej River Basins, the precipitation estimates from the MFGP model are similar to or more accurate than available gridded precipitation products (APHRODITE, TRMM, CRU, bias-corrected WRF). The MFGP model and APHRODITE annual mean precipitation estimates generally agree with each other for this region. The MFGP model predicting slightly higher average precipitation and variance. However, more significant spatial deviations between the MFGP model and APHRODITE over this region appear during the summer monsoon. The MFGP model also presents a more effective spatial resolution of precipitation, generating more structure at finer scales than ERA5 and APHRODITE. MFGP precipitation estimates for the Upper Beas and Sutlej Basins between 1980 and 2013 at a 0.0625° resolution (approx. 9 km) are jointly published with this paper.
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RC1: 'Comment on egusphere-2023-2145', Anonymous Referee #1, 08 Apr 2024
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This paper presents use of multi-fidelity Gaussian processes (MFGPs) to downscale ERA5 precipitation data over high-mountain Asia. The method is validated via application to data-rich Europe and then to a “data-sparse” European scenario before applying it to data-sparse region in the Himalayas. The MFGP method produced similar or more accurate results than existing gridded precipitation products and provided better spatial resolution.
Although I do not have expertise in either machine learning or climatology of Europe or the Himalayas, I have formal training and expertise in applied mathematics and probability and work with precipitation data in mountainous regions of the western U.S. on a daily basis. Thus, I feel qualified to review the mathematical aspects of the paper and its general applicability to the problem of downscaling climate products to mountainous regions.
Overall, this is one of the best scientific papers I have ever read, especially considering its highly technical nature. All aspects of the paper appear to be very carefully prepared, including citation of relevant literature, readability of the text by a broad audience, presentation of methods and results, and technical precision in presentation of the mathematics and statistics.
MFPGs are presented in section 2, which I found to be easy to read and precise. All mathematical formulae appeared to be correct in content and format. More detailed formulae were given in Appendix A. Both the text and Figure 2 provided clear explanation of how the multi-fidelity process works. Specific methods and data sets were clearly described in sections 3 and 4, and the performance metrics were defined in Appendix B. Although these metrics are standard, explicit inclusion in the appendix makes the paper more accessible to a wider audience without detracting from readability of the text.
Results were clearly and concisely presented in Tables 1-3 and Figure 4. In addition, the use of power spectrum density to illustrate data resolution (Figure 6) was appropriate and informative. More detailed results were presented in appendices C and D, again providing more information without detracting from readability of the main text. Sections 6 and 7 concisely presented model applicability to other settings, including both advantages and disadvantages of the MFGP method. The authors have made the full dataset from their analysis available and have also made available their computer code.
I have no suggestions for improvement of the manuscript.
Citation: https://doi.org/10.5194/egusphere-2023-2145-RC1
Data sets
Downscaled ERA5 monthly precipitation data using Multi-Fidelity Gaussian Processes between 1980 and 2012 for the Upper Beas and Sutlej Basins, Himalayas Kenza Tazi https://doi.org/10.5285/b2099787-b57c-44ae-bf42-0d46d9ec87cc
Model code and software
mfgp Kenza Tazi https://github.com/kenzaxtazi/mfgp
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