Xingcai Liu

Multimodel assessment of water scarcity under climate change

Water scarcity severely impairs food security and economic prosperity in many countries today. Expected future population changes will, in many countries as well as globally, increase the pressure on available water resources. On the supply side, renewable water resources will be affected by projected changes in precipitation patterns, temperature, and other climate variables. Here we use a large ensemble of global hydrological models (GHMs) forced by five global climate models and the latest greenhouse-gas concentration scenarios (Representative Concentration Pathways) to synthesize the current knowledge about climate change impacts on water resources. We show that climate change is likely to exacerbate regional and global water scarcity considerably. In particular, the ensemble average projects that a global warming of 2 °C above present (approximately 2.7 °C above preindustrial) will confront an additional approximate 15% of the global population with a severe decrease in water resources and will increase the number of people living under absolute water scarcity (<500 m3 per capita per year) by another 40% (according to some models, more than 100%) compared with the effect of population growth alone. For some indicators of moderate impacts, the steepest increase is seen between the present day and 2 °C, whereas indicators of very severe impacts increase unabated beyond 2 °C. At the same time, the study highlights large uncertainties associated with these estimates, with both global climate models and GHMs contributing to the spread. GHM uncertainty is particularly dominant in many regions affected by declining water resources, suggesting a high potential for improved water resource projections through hydrological model development.

Soil Moisture Drought Monitoring and Forecasting Using Satellite and Climate Model Data over Southwestern China

AbstractIn this paper, an experimental soil moisture drought monitoring and seasonal forecasting framework based on the Variable Infiltration Capacity model (VIC) over southwestern China (SW) is presented. Satellite precipitation data are used to force VIC for a near-real-time estimate of land surface hydrologic conditions. Initialized with satellite-aided monitoring (MONIT), the climate model (CFSv2)-based forecast (MONIT+CFSv2) and ensemble streamflow prediction (ESP)-based forecast (MONIT+ESP) are both performed. One dry season drought and one wet season drought are employed to test the ability of this framework in terms of real-time tracking and predicting the evolution of soil moisture (SM) drought, respectively. The results show that the skillful CFSv2 climate forecasts (CFs) are only found at the first month. The satellite-aided monitoring is able to provide a reasonable estimate of forecast initial conditions (ICs) in real-time mode. In the presented cases, MONIT+CFSv2 forecast exhibits comparable...

Risk and contributing factors of ecosystem shifts over naturally vegetated land under climate change in China.

Identifying the areas at risk of ecosystem transformation and the main contributing factors to the risk is essential to assist ecological adaptation to climate change. We assessed the risk of ecosystem shifts in China using the projections of four global gridded vegetation models (GGVMs) and an aggregate metric. The results show that half of naturally vegetated land surface could be under moderate or severe risk at the end of the 21st century under the middle and high emission scenarios. The areas with high risk are the Tibetan Plateau region and an area extended northeastward from the Tibetan Plateau to northeast China. With the three major factors considered, the change in carbon stocks is the main contributing factor to the high risk of ecosystem shifts. The change in carbon fluxes is another important contributing factor under the high emission scenario. The change in water fluxes is a less dominant factor except for the Tibetan Plateau region under the high emission scenario. Although there is considerable uncertainty in the risk assessment, the geographic patterns of the risk are generally consistent across different scenarios. The results could help develop regional strategies for ecosystem conservation to cope with climate change.

Integrated Environmental Risks

Most environmental risks have been recognized as top global risks in terms of their likelihood and impact (WEF in Global risks 2015. World Economic Forum, Geneva, 2015, The Global Risks Report 2016. World Economic Forum, Geneva, 2016). In recent years, environmental risks facing society are apparently systematic in nature and greatly impaired ecosystem and resulted in huge losses to socioeconomic domain (Briggs in Environmental health 7(1):1–17, 2008). Thus, integrated assessment of environmental risks is necessary for risk management.

Heat Health Risks

High temperature is a natural hazard linking with excess mortality and morbidity (Kovats and Hajat 2008). High temperature can induce heat stroke, communicable disease, cardiovascular disease, and respiratory disease (Basu and Ostro 2008; Hajat et al. 2005).

Projected Changes in Extreme High Temperature and Heat Stress in China

High temperature accompanied with high humidity may result in unbearable and oppressive weather. In this study, future changes of extreme high temperature and heat stress in mainland China are examined based on daily maximum temperature (Tx) and daily maximum wet-bulb globe temperature (Tw). Tw has integrated the effects of both temperature and humidity. Future climate projections are derived from the bias-corrected climate data of five general circulation models under the Representative Concentration Pathways (RCPs) 2.6 and 8.5 scenarios. Changes of hot days and heat waves in July and August in the future (particularly for 2020–50 and 2070–99), relative to the baseline period (1981–2010), are estimated and analyzed. The results show that the future Tx and Tw of entire China will increase by 1.5–5°C on average around 2085 under different RCPs. Future increases in Tx and Tw exhibit high spatial heterogeneity, ranging from 1.2 to 6°C across different regions and RCPs. By around 2085, the mean duration of heat waves will increase by 5 days per annum under RCP8.5. According to Tx, heat waves will mostly occur in Northwest and Southeast China, whereas based on Tw estimates, heat waves will mostly occur over Southeast China and the mean heat wave duration will be much longer than those from Tx. The total extreme hot days (Tx or Tw > 35°C) will increase by 10–30 days. Southeast China will experience the severest heat stress in the near future as extreme high temperature and heat waves will occur more often in this region, which is particularly true when heat waves are assessed based on Tw. In comparison to those purely temperature-based indices, the index Tw provides a new perspective for heat stress assessment in China.

Terrestrial Water Cycle and Water Resources

Driven by the need for water security in a changing environment, research on the water cycle and water resources has attracted intensive research in the last few decades. This chapter reviews the progresses in terrestrial water cycle and water resources research, including the state-of-art understanding of change in the water cycle, improvement of prediction capacities in hydrology and water resources, and achieving water security. The grand challenges and perspectives for the near future are discussed. In particular, we highlight the challenges to address interactions among multiple factors in the water system and to manage the water related risks.

Evaluation of satellite-based evapotranspiration estimates in China

Abstract. Accurate and continuous estimation of evapotranspiration (ET) is crucial for effective water resource management. We used the moderate resolution imaging spectroradiometer (MODIS) standard ET algorithm forced by the MODIS land products and the three-hourly solar radiation datasets to estimate daily actual evapotranspiration of China (ET_MOD) for the years 2001 to 2015. From the point scale validations using seven eddy covariance tower sites, the results showed that the agreement of ET_MOD estimates and observations was higher for monthly and daily values than that of instantaneous values. Under the major river basin and subbasin levels’ comparisons with the variable infiltration capacity hydrological model estimates, the ET_MOD exhibited a slight overestimation in northern China and underestimation in southern China. The mean annual ET_MOD estimates agreed favorably with the hydrological model with coefficients of determination (R2) of 0.93 and 0.83 at major river basin and subbasin scale, respectively. At national scale, the spatiotemporal variations of ET_MOD estimates matched well with those ET estimates from various sources. However, ET_MOD estimates were generally lower than the other estimates in the Tibetan Plateau. This underestimation may be attributed to the plateau climate along with low air temperature and sparsely vegetated surface on the Tibetan Plateau.