The performance of 24 GCMs available in the fifth phase of the Coupled Model Intercomparison Project (CMIP5) is evaluated over the eastern Tibetan Plateau (TP) by comparing the model outputs with ground observations for the period 1961–2005. The twenty-first century trends of precipitation and temperature based on the GCMs’ projections over the TP are also analyzed. The results suggest that for temperature most GCMs reasonably capture the climatological patterns and spatial variations of the observed climate. However, the majority of the models have cold biases, with a mean underestimation of 1.1°–2.5°C for the months December–May, and less than 1°C for June–October. For precipitation, the simulations of all models overestimate the observations in climatological annual means by 62.0%–183.0%, and only half of the 24 GCMs are able to reproduce the observed seasonal pattern, which demonstrates a critical need to improve precipitation-related processes in these models. All models produce a warming trend in the twenty-first century under the Representative Concentration Pathway 8.5 (rcp8.5) scenario; in contrast, the rcp2.6 scenario predicts a lower average warming rate for the near term, and a small cooling trend in the long-term period with the decreasing radiative forcing. In the near term, the projected precipitation change is about 3.2% higher than the 1961–2005 annual mean, whereas in the long term the precipitation is projected to increase 6.0% under rcp2.6 and 12.0% under the rcp8.5 scenario. Relative to the 1961–2005 mean, the annual temperature is projected to increase by 1.2°–1.3°C in the short term; the warmings under the rcp2.6 and rcp8.5 scenarios are 1.8° and 4.1°C, respectively, for the long term.
[1] The hydrological regimes for the major river basins in the Tibetan Plateau (TP), including the source regions of the Yellow (UYE), Yangtze (UYA), Mekong (UM), Salween (US), Brahmaputra (UB), and Indus (UI) rivers, were investigated through a land surface model and regression analyses between climate variables and runoff data. A hydrologic modeling framework was established across the TP to link the Variable Infiltration Capacity (VIC) land surface hydrology model with a degree-day glacier-melt scheme (VIC-glacier model) at a 1/12°Â 1/12°. The model performance was evaluated over the upper basins of the six rivers. The heterogeneity and scarcity of the meteorological stations are the major limitation for hydrological modeling over the TP. The relative contributions to streamflow from rainfall, snowmelt, and glacier melt for the six basins were quantified via the model framework and simulation. The results suggest that monsoon precipitation has a dominant role in sustaining seasonal streamflow over southeastern regions, contributing 65-78% of annual runoff among the UYE, UYA, UM, US, and UB basins. For the UI, the runoff regime is largely controlled by the glacier melt and snow cover in spring and summer. The contribution of glacier runoff is minor for the UYE and UM (less than 2% of total annual flow), and moderate for the UYA and US basins (5-7% of yearly flow), while glacier melt makes up about 12% and 48% of annual flow for the UB and UI basins, respectively.Citation: Zhang, L., F. Su, D. Yang, Z. Hao, and K. Tong (2013), Discharge regime and simulation for the upstream of major rivers over Tibetan Plateau,
The European Centre for Medium-range Weather Forecasts (ECMWF) reanalysis ERA-40, ERA-Interim, University of Washington (UW) data, APHRODITE's Water Resources (APHRODITE), and Tropical Rainfall Measuring Mission (TRMM) Multisatellite Precipitation Analysis (TMPA) precipitation estimates are compared with each other and with the corrected gauge observations over the Tibetan Plateau (TP) at both basin and plateau scales. The ERA-40 generally can capture the broad spatial and temporal distributions in the gauge-based precipitation estimates over the TP. However, the ERA-40 shows little agreement with the gauge-based precipitation in annual variations for the years before 1979. The anticipated improvements in the ERA-Interim precipitation relative to ERA-40 have not been realized in this study. It greatly overestimates the Corrected-China Meteorological Administration (CMA) (by 74-290%) and other datasets, although the ERA-Interim has a better correspondence than ERA-40 with the Corrected-CMA data at both annual and monthly scales among the selected basins. All the products can detect the large-scale precipitation regime, including the monsoon-dominated precipitation in summer and the westerly-wind-induced precipitation in winter. The Corrected-CMA and APHRODITE estimates generally show decreasing trends in summer and increasing trends in spring and winter precipitation during 1961-2007 at both basin and plateau scales. However, the Corrected-CMA shows larger values in trends and more cases with significance than the APHRODITE, suggesting the effects of the undercatch corrections on the precipitation trends. The use of precipitation derived from current reanalysis projects is less preferable for hydrology analysis than the TP observational data at basin scales. However, using gauge-based precipitation datasets as hydrologic model forcings should be careful in the river basins where gauge station network is spare, such as in the Yarlung zangbo river basin. Satellite products still hold a great potential for providing high-resolution precipitation information in remote regions such as the western TP, although more evaluations are needed on the feasibility of satellite precipitation products on the TP where the topography is complex and rainfall rate is highly variable.
Gridded daily precipitation, temperature minima and maxima, and wind speed are generated for the northern Tibetan Plateau (NTP) for 1957–2009 using observations from 81 surface stations. Evaluation reveals reasonable quality and suitability of the gridded data for climate and hydrology analysis. The Mann–Kendall trends of various climate elements of the gridded data show that NTP has in general experienced annually increasing temperature and decreasing wind speed but spatially varied precipitation changes. The northwest (northeast) NTP became dryer (wetter), while there were insignificant changes in precipitation in the south. Snowfall has decreased along high mountain ranges during the wet and warm season. Averaged over the entire NTP, snowfall, temperature minima and maxima, and wind speed experienced statistically significant linear trends at rates of −0.52 mm yr−1 (water equivalent), +0.04°C yr−1, +0.03°C yr−1, and −0.01 m s−1 yr−1, respectively. Correlation between precipitation/wind speed and climate indices characterizing large-scale weather systems for four subregions in NTP reveals that changes in precipitation and wind speed in winter can be attributed to changes in the North Atlantic Oscillation (NAO), the Arctic Oscillation (AO), the East Asian westerly jet (WJ), and the El Niño–Southern Oscillation (ENSO) (wind speed only). In summer, the changes in precipitation and wind are only weakly related to these indices. It is speculated that in addition to the NAO, AO, ENSO, WJ, and the East and South Asian summer monsoons, local weather systems also play important roles.
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