Yanhong Guo

Exploring the water storage changes in the largest lake (Selin Co) over the Tibetan Plateau during 2003–2012 from a basin-wide hydrological modeling

Lake water storage change (ΔSw) is an important indicator of the hydrologic cycle and greatly influences lake expansion/shrinkage over the Tibetan Plateau (TP). Accurate estimation of ΔSw will contribute to improved understanding of lake variations in the TP. Based on a water balance, this study explored the variations of ΔSw for the Lake Selin Co (the largest closed lake on the TP) during 2003–2012 using the Water and Energy Budget-based Distributed Hydrological Model (WEB-DHM) together with two different evapotranspiration (ET) algorithms (the Penman-Monteith method and a simple sublimation estimation approach for water area in unfrozen and frozen period). The contributions of basin discharge and climate causes to the ΔSw are also quantitatively analyzed. The results showed that WEB-DHM could well reproduce daily discharge, the spatial pattern, and basin-averaged values of MODIS land surface temperature (LST) during nighttime and daytime. Compared with the ET reference values estimated from the basin-wide water balance, our ET estimates showed better performance than three global ET products in reproducing basin-averaged ET. The modeled ET at point scale matches well with short-term in situ daily measurements (RMSE = 0.82 mm/d). Lake inflows and precipitation over the water area had stronger relationships with ΔSw in the warm season and monthly scale, whereas evaporation from the water area had remarkable effects on ΔSw in the cold season. The total contribution of the three factors to ΔSw was about 90%, and accounting for 49.5%, 22.1%, and 18.3%, respectively.

Evaluating the complementary relationship of evapotranspiration in the alpine steppe of the Tibetan Plateau

The complementary relationship (CR) of evapotranspiration allows the estimation of the actual evapotranspiration rate (ETa) of the land surface using only routine meteorological data, which is of great importance in the Tibetan Plateau (TP) due to its sparse observation network. With the highest in situ automatic climate observation system in a typical semiarid alpine steppe region of the TP, the wind function of Penman was replaced by one based on the Monin-Obukhov Similarity theory for calculating the potential evapotranspiration rate (ETp); the Priestley-Taylor coefficient, α, was estimated using observations in wet days; and the slope of the saturation vapor pressure curve was evaluated at an estimate of the wet surface temperature, provided the latter was smaller than the actual air temperature. A symmetric CR was obtained between the observed daily actual and potential evapotranspiration. Local calibration of the parameter value (in this order) is key to obtaining a symmetric CR: α, wet environment air temperature (Twea), and wind function. Also, present symmetric CR contradicts previous research that used default parameter values for claiming an asymmetric CR in arid and semiarid regions of the TP. The effectiveness of estimating the daily ETa via symmetric CR was greatly improved when local calibrations were implemented. At the same time, an asymmetric CR was found between the observed daily ETa and pan evaporation rates (Epan), both for D20 aboveground and E601B sunken pans. The daily ETa could also be estimated by coupling the Epan of D20 aboveground and/or E601B sunken pan through CR. The former provided good descriptors for observed ETa, while the latter still tended to overestimate it to some extent.

Plateau Wetlands, an Indispensible Habitat for the Black-Necked Crane (Grus nigricollis) - A Review

As a highly productive and sensitive ecosystem, plateau wetlands provide indispensable habitats for Grus nigricollis, an endangered species of crane. However, the destruction and degeneration of plateau wetlands caused by climate change and human disturbance have influenced the habitats and biological behaviors of Grus nigricollis. Previous studies have ignored the importance of particular habitats to the continued existence of Grus nigricollis, especially with regard to extremely fragile plateau wetland systems. In this review, the importance of plateau wetlands for the breeding, overwintering and foraging of Grus nigricollis is summarized; the impact of human activities and climate change on Grus nigricollis and on plateau wetland habitats is also presented. Further monitoring and research is required to produce substantive suggestions vis-à-vis future, and better, conservation of Grus nigricollis and its habitats.

Spatiotemporal variations of actual evapotranspiration over the Lake Selin Co and surrounding small lakes (Tibetan Plateau) during 2003–2012

Actual evapotranspiration (ETa) over the Tibetan Plateau (TP) is an important component of the water cycle, and greatly influences the water budgets of the TP lake basins. Quantitative estimation of ETa within lake basins is fundamental to physically understanding ETa changes, and thus will improve the understanding of the hydrological processes and energy balance throughout the lake basins. In this study, the spatiotemporal dynamic changes of ETa within the Lake Selin Co (the TP’s largest lake) and its surrounding small lakes and land area during 2003–2012 are examined at the basin scale. This was carried out using the well-established Water and Energy Budget-based Distributed Hydrological Model (WEB-DHM) for the land area, the Penman method for the water area when unfrozen, and a simple sublimation estimation approach for the water area when frozen. The relationships between ETa changes and controlling factors are also discussed. Results indicate that the simulated land ETa from the WEB-DHM reasonably agrees with the estimated ETa values from the nonlinear complementary relationship model using appropriately calibrated parameter values at a point scale. Land ETa displayed a non-significant increase of 7.03 mm year−1, and largely depends on precipitation. For the water area, the combined effects of reduced wind speed and net radiation offset the effect of rising temperature and vapor pressure deficit, and contributed to a non-significant decrease in evaporation of 4.17 mm year−1. Sensitivity analysis shows that vapor pressure deficit and wind speed are the most sensitive variables to the changes of evaporation from the water area.

Permafrost soil water content evaluation using high-frequency ground-penetrating radar in Amdo catchment, Central Tibetan Plateau

High-frequency ground-penetrating radar (GPR) was applied to assess soil water content spatially during the freezing periods at a continuous permafrost site in Amdo catchment, which is centrally located in Tibetan Plateau. The active layer thickness was also roughly presented through the whole survey, which traveled almost 15Km from the top of a hill towards a seasonal stream. The results revealed that average soil moisture increased slightly towards the down-slope direction and kept a higher level near the stream, especially in the deeper layers. Moreover, we found that active layer depth varied with topography, and it ranged from 1.92m to 2.44m along the profile. The topography (i.e. slope and elevation) and stream distribution significantly alter spatial pattern of soil moisture and active layer thickness in the study regions.

Quantitative comparison of river inflows to a rapidly expanding lake in central Tibetan Plateau

The recent rapid expansion of inland lakes on the Tibetan Plateau (TP) are a good indicator of the consequences of climate change. Quantifying the hydrological cycle of the lake basin is fundamentally important to understand the causes of lake growth. However, the hydrological processes of the TP interior are very complex and difficult to investigate because of the lack of observations. This is especially true for estimating the lake changes when run-off inflows are affected by small lakes located in the flow routes within drainage areas. We used an integrated hydrological model, in combination with glacier melt and lake retention models, to analyse the run-off inflows to Lake Siling Co, the largest endorheic lake in Tibet. It includes four subdrainage basins: Zhajiazangbu, Zhagenzangbu, Alizangbu, and Boquzangbu. Lake Siling Co was characterized by considerable increases during warm season from 1981 to 2012, due to the increased run-off from Zhajiazangbu accounting for about 51-62% of the total run-off inflows. Moreover, the dramatic increases exhibited during cold seasons were related to the increased retention water released from the small lakes within Zhagenzangbu and Alizangbu. Of the studied subdrainage basins, Boquzangbu contributed the least during both warm and cold seasons. On average, the annual amount of evaporation from lakes within the drainage area was about 2 times greater than that of glacier melt run-off. Our results suggest that the retention effects of lakes on river inflows should receive more attention, because understanding these effects is potentially crucial to improved understanding of lake variations in the TP.