Weicai Wang

A First-order Method to Identify Potentially Dangerous Glacial Lakes in a Region of the Southeastern Tibetan Plateau

Abstract Though glacial lake outburst floods have become an urgent issue on the Tibetan Plateau, no standardized methods have been proposed so far to identify and prioritize potentially dangerous glacial lakes (PDGLs). Here, we developed a first-order approach to identify PDGLs in the Boshula Mountain Range, southeastern Tibetan Plateau. Five variables—mother glacier area, distance between lake and glacier terminus, slope between lake and glacier, mean slope of moraine dam, and mother glacier snout steepness—were selected to identify PDGLs on the basis of four criteria we suggested. A fuzzy consistent matrix method was then applied to determine the weight of variables, and characteristic statistical values were used as thresholds to classify each variable. Out of 78 moraine-dammed lakes studied, we identified 8 glacial lakes as potentially very highly dangerous. We also validated our approach with 6 drained glacial lakes inside and outside our study area. Successfully identifying them as potentially very highly and/or highly dangerous lakes demonstrates the validity of the method.

Extensive and drastically different alpine lake changes on Asia's high plateaus during the past four decades

Asias high plateaus are sensitive to climate change and have been experiencing rapid warming over the past few decades. We found 99 new lakes and extensive lake expansion on the Tibetan Plateau during the last four decades, 1970-2013, due to increased precipitation and cryospheric contributions to its water balance. This contrasts with disappearing lakes and drastic shrinkage of lake areas on the adjacent Mongolian Plateau: 208 lakes disappeared, and 75% of the remaining lakes have shrunk. We detected a statistically significant coincidental timing of lake area changes in both plateaus, associated with the climate regime shift that occurred during 1997/1998. This distinct change in 1997/1998 is thought to be driven by large-scale atmospheric circulation changes in response to climate warming. Our findings reveal that these two adjacent plateaus have been changing in opposite directions in response to climate change. These findings shed light on the complex role of the regional climate and water cycles and provide useful information for ecological and water resource planning in these fragile landscapes.

Lake volume and groundwater storage variations in Tibetan Plateau's endorheic basin

The Tibetan Plateau (TP), the highest and largest plateau in the world, with complex and competing cryospheric‐hydrologic‐geodynamic processes, is particularly sensitive to anthropogenic warming. The quantitative water mass budget in the TP is poorly known. Here we examine annual changes in lake area, level, and volume during 1970s–2015. We find that a complex pattern of lake volume changes during 1970s–2015: a slight decrease of −2.78 Gt yr−1 during 1970s–1995, followed by a rapid increase of 12.53 Gt yr−1 during 1996–2010, and then a recent deceleration (1.46 Gt yr−1) during 2011–2015. We then estimated the recent water mass budget for the Inner TP, 2003–2009, including changes in terrestrial water storage, lake volume, glacier mass, snow water equivalent (SWE), soil moisture, and permafrost. The dominant components of water mass budget, namely, changes in lake volume (7.72 ± 0.63 Gt yr−1) and groundwater storage (5.01 ± 1.59 Gt yr−1), increased at similar rates. We find that increased net precipitation contributes the majority of water supply (74%) for the lake volume increase, followed by glacier mass loss (13%), and ground ice melt due to permafrost degradation (12%). Other term such as SWE (1%) makes a relatively small contribution. These results suggest that the hydrologic cycle in the TP has intensified remarkably during recent decades.

Short-term variability in the dates of the Indian monsoon onset and retreat on the southern and northern slopes of the central Himalayas as determined by precipitation stable isotopes

AbstractnThis project launched the first study to compare the stable isotopes (δ18O and δD) in daily precipitation at Kathmandu (located on the southern slope of the central Himalayas) and Tingri (located on the northern slope). The results show that low δ18O and δD values of summer precipitation at the two stations were closely related to intense convection of the Indian monsoon. However, summer δ18O and δD values at Tingri were lower than those at Kathmandu, a result of the lift effect of the Himalayas, coupled with convection disturbances and lower temperatures at Tingri. In winter, the relatively high δ18O and δD values at the two stations appears to have resulted from the influence of the westerlies. Compared with those during the summer, the subsidence of the westerlies and northerly winds resulted in relatively high δ18O and δD values of the winter precipitation at Tingri. Winter δ18O and δD values at Kathmandu far exceeded those at Tingri, due to more intense advection of the southern branch of the westerlies, and higher temperatures and relative humidity at Kathmandu. The detailed differences in stable isotopes between the two stations follow short-term variability in the onset date of the Indian monsoon and its retreat across the central Himalayas. During the sampling period, the Indian monsoon onset at Tingri occurred approximately 1xa0week later than that at Kathmandu. However, the retreat at Tingri began roughly 3xa0days earlier. Clearly, the duration of the Indian monsoon effects last longer at Kathmandu than that at Tingri. Our findings also indicate that the India monsoon travels slowly northward across the central Himalayas due to the blocking of the Himalayas, but retreats quickly.

Atmospheric transport and accumulation of organochlorine compounds on the southern slopes of the Himalayas, Nepal

Studies have been devoted to the transport and accumulation of persistent organic pollutants (POPs) in mountain environments. The Himalayas have the widest altitude gradient of any mountain range, but few studies examining the environmental behavior of POPs have been performed in the Himalayas. In this study, air, soil, and leaf samples were collected along a transect on the southern slope of the Himalayas, Nepal (altitude: 135-5100xa0m). Local emission occurred in the lowlands, and POPs were transported by uplift along the slope. During the atmospheric transport, the HCB proportion increased from the lowlands (20%) to high elevation (>50%), whereas the proportions of DDTs decreased. The largest residue of soil POPs appeared at an altitude of approximately 2500xa0m, and may be related to absorption by vegetation and precipitation. The net deposition tendencies at the air-soil surface indicated that the Himalayas may be a sink for DDTs and PCBs.

Methods for assessing regional glacial lake variation and hazard in the southeastern Tibetan Plateau: a case study from the Boshula mountain range, China

Glaciers on the Tibetan Plateau are undergoing an accelerating retreat under climatic warming, with the immediate result of glacial lake outburst floods (GLOFs) becoming increasingly frequent. Glacial lakes in the southeast of the Tibetan Plateau are densely distributed. Due to the difficulties associated with field investigations of glacial lakes, including remote locations and harsh weather conditions, methods which combine remote sensing, geographic information systems and hydrodynamic modeling (HEC-RAS) with field investigation were developed to assess regional glacial lake variation and hazard. The methods can be divided into three levels. At the first level, multi-temporal satellite images were used to (1) study the variation of glacial lakes for the whole region during recent decades, as well as (2) qualitatively identify potentially dangerous glacial lakes (PDGLs). The second level is an in-depth evaluation of the degree of danger for selected PDGLs by ground-based surveys, and then verification of the first-level results. At the third level, the one-dimensional (1D) hydrodynamic model HEC-RAS was used to simulate the inundation characteristics of hypothetical outburst of PDGLs. The three levels downscale from the whole study area to individual PDGLs, and thus assess the hazard of glacial lakes progressively. The methods were then applied to a region of southeastern Tibet—the Boshula mountain range—to analyze the variation of glacial lakes and assess potential hazards posed by GLOFs. Since these methods employ easily accessible data and instruments, the application in other regions is promising.

Retreat rates of debris-covered and debris-free glaciers in the Koshi River Basin, central Himalayas, from 1975 to 2010

Debris-covered glaciers are common in the Himalayas and play a key role in understanding future regional water availability and management. Previous studies of regional glacial changes have often neglected debris-covered glaciers or have mixed them with debris-free glaciers. In this study, we generated a new glacier data set that includes debris-covered and debris-free glaciers to study the glacial surface area change in the Koshi River Basin in the central Himalayas. Long time-series Landsat data were used to extract the glacier boundaries using automatic and manual classification methods. The glacial area decreased by 10.4% from 1975 to 2010 at a rate of 0.30%xa0a−1, with accelerated melting since 2000 (0.47%xa0a−1). Small glaciers melted faster than large glaciers. In terms of distinctive glacier types, debris-free glaciers shrank at a rate of 0.45%xa0a−1, faster than debris-covered glaciers (0.18%xa0a−1), while debris-covered glaciers larger than 5.0xa0km2 retreated at a rate faster than debris-free glaciers of the same-sized group. We also studied the potential interactions between 222 supraglacial lakes and debris-covered glaciers. Debris-covered glaciers with glacial lakes melt faster than glaciers without lakes. This study can improve our understanding of the differences in the changes between debris-covered and debris-free glaciers in the central Himalayas and help evaluate water resource changes in the Himalayas.

Superconductivity in hot pressing YBaCuO system and chemically doped R(Er, F)YBaCuO system

Abstract In this paper, the study on hot pressing of YBaCuO system and chemically doped ErYBa 2 Cu 3 O x and YBa 2 Cu 3 (OF) x superconducting oxides were reported. The starting oxides were sintered at 0.04 GPa and 1123 K for a few minutes, then cooling down and unloading slowly, the four probe resistance and a.c. magnetic susceptibility measurements showed that the hot pressed samples were superconductor with onset transition temperature ( T cn above LN 2 temperature. Zero transition temperature ( T c0 of chemically doped samples was higher than that of YBaCuO system.