Zhenchun Hao

Evaluation of the Global Climate Models in the CMIP5 over the Tibetan Plateau

AbstractThe 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 tre...

Climate Change on the Northern Tibetan Plateau during 1957–2009: Spatial Patterns and Possible Mechanisms

AbstractGridded 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 an...

Entropy-Based Method for Bivariate Drought Analysis

AbstractDrought duration and severity are two main properties for characterizing droughts. These drought properties are mutually correlated and may have different marginal distributions. A bivariate (or joint) distribution of drought duration and severity is therefore needed that is capable of accommodating their different marginal distributions. This study proposes a method, based on entropy theory, for constructing the bivariate distribution of drought duration and severity with different marginal distribution forms. By specifying constraints for drought duration and severity, the entropy-based bivariate distribution can be derived and then marginal distributions can be obtained accordingly. Monthly streamflow data from Brazos River at Waco, Texas, are employed to illustrate the application of the proposed method to model drought duration and severity for drought analysis. The copula method is also applied for comparison with the proposed entropy method.

Review of Advances in Hydrologic Science in China in the Last Decades: Impact Study of Climate Change and Human Activities

Water is a precious resource and plays a critical role in socioeconomic development in many sectors. Since the completion of a nationwide assessment of water resources by China’s Ministry of Water Resources (MWR) in 1986, a number of research papers with national perspectives have appeared in Chinese journals and have become major references for a variety of issues related to water resources (Qian 1991). Responding to international scientific research programs such as International Geosphere-Biosphere Programme Biosphere Aspects of the Hydrological Cycle (IGBPBAHC), World Climate Research Programme (WCRP), Global Energy and Water Cycle Experiment/GEWEX Asian Monsoon Experiment (GEWEX/GAME) (Xia and Tan 2002), and the social and economic development demands in China, a series of key projects on hydrologic research in supporting water resources management have been implemented particularly in the last 10 years in the 21st century, funded by the National Natural Science Foundation of China (NSFC), Chinese Academy of Sciences (CAS), Chinese Academy of Engineering (CAE), MWR, and Ministry of Science and Technology (MOST). These projects were designed to address the role of hydrologic changes in flood and drought-hazard mitigation, water shortages, and ecosystem degradation with respect to the impacts of climate change and human activities in China (Qian and Zhang 2001; Xia and Chen 2001; Liu and Zheng 2002; Zhang and Wang 2007; Wang et al. 2002). In this paper, the writers strive to summarize recent advances of hydrologic impact research in response to climate change and human activities in China. The primary discussion is focused on three key points, as follows: (1) the spatiotemporal changes of various components for water cycle processes, including precipitation, runoff, and evapotranspiration investigations, are summarized and addressed; (2) recent efforts in hydrologic studies in China associated with lakes, glaciers, and snow are reviewed; and (3) challenges and opportunities in hydrologic science in China are discussed as highlights.

Entropy-Based Parameter Estimation for Extended Three-Parameter Burr III Distribution for Low-Flow Frequency Analysis

Low-flow analysis is important for management of water supply and droughts, determining the health of ecosystems, and for sustained agriculture. Two entropy-based methods, the ordinary entropy (ENT) method and the parameter space expansion method (PSEM), are employed for estimating parameters of the extended Burr III distribution, which is useful for low-flow frequency analysis. With parameters estimated in this manner, the extended Burr III distribution is applied to six low-flow datasets, and quantiles (discharges) corresponding to different return periods are computed. These return periods are then compared with those when the extended Burr III distribution parameters are estimated using the methods of moments (MOM), probability weighted moments (PWM), and maximum likelihood estimation (MLE). It is shown that PSEM yields the same quantiles as does MLE for discrete cases, while ENT is found comparable to MOM and PWM. The quantile (discharge) values estimated by the four methods are close to each other for smaller return periods, but large differences occur for long return periods.

The analysis of water vapor budget and its future change in the Yellow‐Huai‐Hai region of China

This study aims to analyze the atmospheric water vapor budget changes in the Yellow-Huai-Hai River basin and explore the possible relationship between water vapor budget and precipitation. The Fifth Phase of the Coupled Model Intercomparison Project is used to assess the future change of water vapor in the region. Corrected general circulation model outputs are evaluated, and multimodel ensemble is used to project the future atmospheric water vapor changes. Results show the following: (1) Water vapor in wet summer, which is transported from Bengal Bay and west Pacific Ocean and accounts for the largest part of annual transport, has similar distribution with precipitation in the study area; (2) Strong evidences indicate significant relationships between the precipitation and water vapor in humid area and semihumid area, but poor relationship in semiarid area; (3) The future climate of the region is projected to be wetter but has a “dry belt” located in the Hai River basin, the north of the Huai River basin and the southeast of the Yellow River basin during 2020s, which will reduce rapidly afterward; (4) Summer water vapor changes depend mainly on the meridional transport. The changes under RCP4.5 scenario are smaller than that under RCP8.5 and the increases are more significantly in 2080s under both scenarios. The water vapor has a larger increase in the Huai River basin than that in the other two basins. Future water vapor changes will likely lead to exacerbated problems caused by the uneven distribution of precipitation and produce serious challenges to water resource management in agriculture, industry and the environment.

Recognition the Spatio-temporal Patterns of Low-flow Changes in the Yellow River over the Last Half Century

Low flow is widely regarded as the primary flow conditions for the anthropogenic and aquatic communities in most rivers, particularly in such an arid and semi-arid area as the Yellow River. In this study, a procedure combining Mann-Kendall trend test, wavelet transform analysis and spatial mapping techniques is presented to identify the spatio-temporal patterns of low-flow changes in the Yellow River (1955-2005). The results indicate that: 1) no trends can be detected in the major low-flow conditions in the upper Yellow River, while downward trends can be observed in the middle and lower Yellow River; 2) similar patterns of periodicity are detected in the 7-day min (AM7Q) in the upper and middle Yellow River, while different patterns are found in the lower Yellow River; 3) the increasing coefficients of variance of primary low-flow conditions suggest the variability of the low flow is increasing from the upper to lower stream; 4) climate changes and uneven temporal-spatial patterns of precipitation, jointly with highly intensive water resource utilization, are recognized as major factors led to the decreasing of low-flow in the lower Yellow River in recent decades. The current investigation will be beneficial to regional water resources management for the Yellow River basin, characterized by serious water shortage.

Simulation of Seasonally Frozen Soil Freezing-Thawing Processes and the Spatial Distribution of Active Layer Depths Based on Modis Data in the Three-River Source Region, China

The processes of soil freezing-thawing lead to soil water and heat movement in cold regions, which significantly influences the hydrological and energy cycles in the soil-plantatmosphere system. This research presented a soil water content coupled with heat transfer model based on physical processes of water and heat movement in frozen soil. The model was calibrated and validated using the measured data of soil temperature and active soil depths at 19 stations in and around the Three-River Source Region of China. The results showed that the frozen soil model capture the processes of soil freezing-thawing well at this region. The relationship between model parameters and climate and vegetation factors was analyzed using the observation data and remote sensing data obtained by MODIS, and results showed that the model parameter c has a better correlation with longitude and vegetation coverage. A multi-regression model was established to estimate the model parameters in regions without observation data and its determination coefficient R2 was 0.82. The mean relative error between calibration and inversion parameters of 19 stations is 6.29%. Thus, the proposed method can be applied to cold regions without observation data to obtain the parameters and simulated the soil freezing-thawing processes.

Statistical properties of climatic variables in the head region of the yellow river

On the basis of the precipitation, mean air temperature, relative humidity and wind speed at 10 meteorological stations in the head region of the Yellow River from 1960-1997, the long-term monotonic trends and periods for the four climate variables have been investigated. Mann-Kendall method and wavelet transform analysis were employed to analyze changing trends and potential periods for the climatic variables. The results show that regional annual air temperature has an increasing trend while annual precipitation, relative humidity and wind speed indicate a slightly descending trend but no significant increasing or decreasing trend is identified. At principal period scale, periodical oscillation for the time series of meteorological factors are evident in the wavelet coefficients contours map. The research could facilitate the understanding of natural process and contribute to regional water resources management in the head region of the Yellow River.

Variable evaluation model and its application on the assessment of river ecosystem health

The evaluation of river ecosystem health is significant for the sustainable development of cities. In practical application, evaluation criteria are shown in interval pattern. However, in some commonly used methods, evaluation criteria of discrete values are often taken. Furthermore, the simplification of index from interval pattern to the point value form affects the rationality and accuracy of evaluation. The fuzzy variable model can solve this problem by combining with multiple attribute intervals. Based on this method, the ecosystem health of a river was assessed. Results show that the model is applicable in the assessment of river ecosystem health with more reliability.