Jianshi Zhao

Bio: Jianshi Zhao is an academic researcher from Tsinghua University. The author has contributed to research in topics: Water resources & Drainage basin. The author has an hindex of 22, co-authored 62 publications receiving 1376 citations. Previous affiliations of Jianshi Zhao include University of Illinois at Urbana–Champaign.

South-to-North Water Diversion stabilizing Beijing’s groundwater levels

Abstract: Groundwater (GW) overexploitation is a critical issue in North China with large GW level declines resulting in urban water scarcity, unsustainable agricultural production, and adverse ecological impacts. One approach to addressing GW depletion was to transport water from the humid south. However, impacts of water diversion on GW remained largely unknown. Here, we show impacts of the central South-to-North Water Diversion on GW storage recovery in Beijing within the context of climate variability and other policies. Water diverted to Beijing reduces cumulative GW depletion by ~3.6 km3, accounting for 40% of total GW storage recovery during 2006–2018. Increased precipitation contributes similar volumes to GW storage recovery of ~2.7 km3 (30%) along with policies on reduced irrigation (~2.8 km3, 30%). This recovery is projected to continue in the coming decade. Engineering approaches, such as water diversions, will increasingly be required to move towards sustainable water management. The authors here address water sustainability in the greater area of Beijing, China. Specifically, the positive effects towards Beijing groundwater levels via water diversion from the Yangtze River to the North are shown.

Deceleration of China's human water use and its key drivers

Abstract: Increased human water use combined with climate change have aggravated water scarcity from the regional to global scales. However, the lack of spatially detailed datasets limits our understanding of the historical water use trend and its key drivers. Here, we present a survey-based reconstruction of China’s sectoral water use in 341 prefectures during 1965 to 2013. The data indicate that water use has doubled during the entire study period, yet with a widespread slowdown of the growth rates from 10.66 km3⋅y−2 before 1975 to 6.23 km3⋅y−2 in 1975 to 1992, and further down to 3.59 km3⋅y−2 afterward. These decelerations were attributed to reduced water use intensities of irrigation and industry, which partly offset the increase driven by pronounced socioeconomic development (i.e., economic growth, population growth, and structural transitions) by 55% in 1975 to 1992 and 83% after 1992. Adoptions for highly efficient irrigation and industrial water recycling technologies explained most of the observed reduction of water use intensities across China. These findings challenge conventional views about an acceleration in water use in China and highlight the opposing roles of different drivers for water use projections.

Improved Dynamic Programming for Hydropower Reservoir Operation

Abstract: The writers propose a successive improved dynamic programming (SIDP) algorithm for hydropower reservoir operation based on an analysis of concavity, complementarity, and monotonicity of hydropower problems. For single-period hydropower generation, storage and release have diminishing marginal contributions to hydropower generation (i.e., concavity), and there is also a complementary effect between storage and release (i.e., release becomes more productive in accordance with increasing storage). For multiple-period hydropower generation, the complementarity influences the concavity of the objective function and the monotonicity of operation decisions, and is the major cause of complexity in hydropower operation. With mathematical derivations, the writers propose a concave approximation to the hydropower generation function and a SIDP algorithm for hydropower reservoir operation. The efficiency of SIDP is demonstrated with two hypothetical case studies of long-term hydropower scheduling, which shows...

Identifying effective forecast horizon for real-time reservoir operation under a limited inflow forecast

Abstract: [1] The use of a streamflow forecast for real-time reservoir operation is constrained by forecast uncertainty (FU) and limited forecast horizon (FH). The effects of the two factors are complicating since increasing the FH usually provides more information for decision making in a longer time framework but with increasing uncertainty, which offsets the information gain from a longer FH. This paper illustrates the existence of an effective FH (EFH) with a given forecast, which balances the effects of the FH and FU and provides the maximum information for reservoir operation decision making. With the assumption of a concave objective function, a monotonic relationship between current operation decision and ending storage is derived. Metrics representing the error resulting from a limited forecast relative to a perfect forecast are defined to evaluate reservoir performance. Procedures to analyze the complicating effect of FU and FH and to identify EFH are proposed. Results show that: (1) when FH is short, FH is the dominating factor for determining reservoir operation, and reservoir performance exhibits a quick improvement as FH increases; (2) when FH is long, the inflow information may be too uncertain to guide reservoir operation decisions and FU becomes the dominating factor; and (3) at a medium FH, reservoir performance depends on the complicating effects of FU and FH and EFH locates with a certain balanced level of FU and FH. The statistical characteristics of EFH are illustrated with case studies with deterministic forecast and ensemble forecast. Moreover, the impacts of temporal correlation of FU, inflow variability, evaporation loss, and reservoir capacity on EFH are explored.

The Ensemble Kalman Filter: Theoretical formulation and practical implementation

Abstract: The purpose of this paper is to provide a comprehensive presentation and interpretation of the Ensemble Kalman Filter (EnKF) and its numerical implementation. The EnKF has a large user group, and numerous publications have discussed applications and theoretical aspects of it. This paper reviews the important results from these studies and also presents new ideas and alternative interpretations which further explain the success of the EnKF. In addition to providing the theoretical framework needed for using the EnKF, there is also a focus on the algorithmic formulation and optimal numerical implementation. A program listing is given for some of the key subroutines. The paper also touches upon specific issues such as the use of nonlinear measurements, in situ profiles of temperature and salinity, and data which are available with high frequency in time. An ensemble based optimal interpolation (EnOI) scheme is presented as a cost-effective approach which may serve as an alternative to the EnKF in some applications. A fairly extensive discussion is devoted to the use of time correlated model errors and the estimation of model bias.

Precautionary Saving in the Small and in the Large

Abstract: The theory of precautionary saving is shown in this paper to be isomorphic to the Arrow-Pratt theory of risk aversion, making possible the application of a large body of knowledge about risk aversion to precautionary saving, and more generally, to the theory of optimal choice under risk In particular, a measure of the strength of precautionary saving motive analogous to the Arrow-Pratt measure of risk aversion is used to establish a number of new propositions about precautionary saving, and to give a new interpretation of the Oreze-Modigliani substitution effect

Trading-off Fish Biodiversity, Food Security and Hydropower in the Mekong River Basin

Abstract: The Mekong River Basin, site of the biggest inland fishery in the world, is undergoing massive hydropower development. Planned dams will block critical fish migration routes between the river's downstream floodplains and upstream tributaries. Here we estimate fish biomass and biodiversity losses in numerous damming scenarios using a simple ecological model of fish migration. Our framework allows detailing trade-offs between dam locations, power production, and impacts on fish resources. We find that the completion of 78 dams on tributaries, which have not previously been subject to strategic analysis, would have catastrophic impacts on fish productivity and biodiversity. Our results argue for reassessment of several dams planned, and call for a new regional agreement on tributary development of the Mekong River Basin.

Evaluation of groundwater depletion in North China using the Gravity Recovery and Climate Experiment (GRACE) data and ground-based measurements (EI)

Abstract: [1] Changes in regional groundwater storage in North China were estimated from the Gravity Recovery and Climate Experiment (GRACE) satellites data and ground-based measurements collected from 2003 to 2010. The study area (∼370,000 km2) included the Beijing and Tianjin municipality, the Hebei and Shanxi province, which is one of the largest irrigation areas in the world and is subjected to intensive groundwater-based irrigation. Groundwater depletion in North China was estimated by removing the simulated soil moisture changes from the GRACE-derived terrestrial water storage changes. The rate of groundwater depletion in North China based on GRACE was 2.2 ± 0.3 cm/yr from 2003 to 2010, which is equivalent to a volume of 8.3 ± 1.1 km3/yr. The groundwater depletion rate estimated from monitoring well stations during the same time period was between 2.0 and 2.8 cm/yr, which is consistent with the GRACE-based result. However, the estimated groundwater depletion rate in shallow plain aquifers according to the Groundwater Bulletin of China Northern Plains (GBCNP) for the same time period was only approximately 2.5 km3/yr. The difference in groundwater depletion rates estimated from GRACE and GBCNP data indicates the important contribution of groundwater depletion from deep aquifers in the plain and piedmont regions of North China.