Machine learning method is an alternative for the hydrological model in an alpine catchment in the Tianshan region, Central Asia

Study region: Kaidu River catchment in the Tianshan Mountain, northwestern China. Study focus: This paper compared the applicability and accuracy of four machine learning models and two hydrological ones to simulate the daily streamflow and extreme streamflow of the Kaidu River catchment. The machine learning models are Support Vector Regression (SVR), eXtreme Gradient Boosting (XGBoost), Random Forests (RF), and Long Short-Term Memory (LSTM), while the hydrological models are the Soil and Water Assessment Tool (SWAT) and the extended SWAT with a glacier dynamic module (SWAT-Glacier). New hydrological insights for the region: LSTM achieved better model performance in simulating daily streamflow than SWAT and SWAT-Glacier, with Kling-Gupta efficiency of 0.92, 0.82, and 0.80, respectively. Meanwhile, SVR, XGBoost, and RF showed satisfactory performance, with KGE of 0.67, 0.71, and 0.70, respectively. LSTM, SWAT and SWAT-Glacier could well simulate the annual peak flow (i.e., annual maximum 1-day streamflow and 5-day average streamflow) but failed to mimic the annual minimum 7-day average streamflow, with PBIAS exceeding 28%. Furthermore, all the models failed to reproduce the dates of hydrological extremes. Nevertheless, using the quantile loss function in the LSTM model resulted in significantly improved model performance in the low streamflow indices, compared to that using mean squared error as the loss function. Overall, LSTM could be a good alternative for simulating daily streamflow and extreme streamflow in data-scarce catchments

The First Inventory of Rock Glaciers in the Zhetysu Alatau: The Aksu and Lepsy River Basins

While rock glaciers (RGs) are widespread in the Zhetysu Alatau mountain range of Tien Shan (Kazakhstan), they have not yet been systematically investigated. In this study, we present the first rock glacier inventory of this region containing 256 rock glaciers with quantitative information about their locations, geomorphic parameters, and downslope velocities, as established using a method that combines SAR interferometry and optical images from Google Earth. Our inventory shows that most of the RGs are talus-derived (61%). The maximum downslope velocity of the active rock glaciers (ARGs) was 252 mm yr−1. The average lower height of rock glaciers in this part of the Zhetysu Alatau was 3036 m above sea level (ASL). The largest area of rock glaciers was located between 2800 and 3400 m ASL and covered almost 86% of the total area. Most rock glaciers had a northern (northern, northeastern, and northwestern) orientation, which indicated the important role of solar insolation in their formation and preservation

Accelerated Glacier Area Loss in the Zhetysu (Dzhungar) Alatau Range (Tien Shan) for the Period of 1956–2016

An updated glacier inventory is important for understanding the current glacier dynamics in the conditions of actual accelerating glacier retreat observed around the world. Here, we present a detailed analysis of the glaciation areas of the Zhetysu Alatau Range (Tien Shan) for 1956–2016 using well-established semiautomatic methods based on the band ratios. The total glacier area decreased by 49 ± 2.8% or by 399 ± 11.2 km2 from 813.6 ± 22.8 km2 to 414.6 ± 11.6 km2 during 1956–2016, while the number of glaciers increased from 985 to 813. Similar rates of area change characterized the periods 1956–2001, 2001–2012, 2012–2016, and 2001–2016: −296.2 ± 8.3 (−0.8% a−1), −63.7± 1.8 (−1.1% a−1), −39.1 ±1.1 (−2.2% a−1) and −102.8 ± 2.9 (−1.3% a−1) km2, respectively. The mean glacier size decreased from 0.57 km2 in 2001 to 0.51 km2 in 2016. Most glaciation areas of the Zhetysu Alatau faced north (north, northwest, and northeast), covered 390.35 ± 11 km2, and were located in altitudes between 3000 and 4000 m.a.s.l. With shrinkage rates of about −0.8% and −1.3% a−1 for the periods of 1956–2001 and 2001–2016, our results show that study area has the highest shrinkage rate compared to other glacierized areas of Central Asian mountains, including Altai, Pamir, and even the inner ranges of Tien Shan. It was found that a significant increase in temperature (0.12 °C/10 years) plays a main role in the state of glaciers