The lateral movement of soil carbon has a profound effect on the carbon budget of terrestrial ecosystems; however, it has never been quantified in China, which is one of the strongest soil erosion areas in the world. In this study, we estimated that the overall soil erosion in China varies from 11.27 to 18.17 Pg yr−1 from 1982 to 2011, accounting for 7–21% of total soil erosion globally. Soil erosion induces a substantial lateral redistribution of soil organic carbon ranging from 0.64 to 1.04 Pg C yr−1. The erosion-induced carbon flux ranges from a 0.19 Pg C yr−1 carbon source to a 0.24 Pg C yr−1 carbon sink in the terrestrial ecosystem, which is potentially comparable in magnitude to previously estimated total carbon budget of China (0.19 to 0.26 Pg yr−1). Our results showed that the lateral movement of soil carbon strongly alters the carbon budget in China, and highlighted the urgent need to integrate the processes of soil erosion into the regional or global carbon cycle estimates.

Evapotranspiration (ET) combines the land‐atmosphere water, energy, and carbon cycles and plays a critical role in climate studies. However, ET is difficult to quantify accurately. This study compares three 1982–2013 ET data sets for China based on surface water balance values, a modified Penman‐Monteith (MPM) model and reanalysis data. Water balance ET data, which have been widely used as benchmark data for regional ET, were calculated with and without considering reservoir water storage. MPM ET values were calculated from combinations of input data from different sources, including solar radiation and meteorological data. The MPM model is primarily energy determined, although the impacts of vegetation, soil moisture, air temperature, and wind speed on ET are also considered. The reanalysis ET data used in this study are derived from atmospheric and off‐line land reanalyses. We examined their spatial patterns, interannual variabilities, trends, and key drivers. We found that MPM ET is consistent with water balance ET in detecting ET trends for 1997 to 2013, whereas reanalysis ET is not. The trends and interannual variabilities of ET found via reanalyses are primarily determined by precipitation patterns. However, the precipitation data derived from the atmospheric reanalyses present significant uncertainties. Off‐line land reanalyses correct these biases but do not consider terrestrial water storage changes resulting from reservoir construction and interannual variability in vegetation. Both omissions may produce unreliable trends of ET in reanalyses for China. This study will help improve current ET simulations and contribute to further extending climate studies.

Evapotranspiration (ET) is usually difficult to estimate at the regional scale due to scarce direct measurements. This study uses the water balance equation to calculate the regional ET with observations of precipitation, runoff, and terrestrial water storage changes (TWSC) in nine exorheic catchments of China. We compared the regional ET estimates from a water balance perspective with and without considering TWSC (ETWB: ET estimates with considering TWSC, and ETPQ: ET estimates from precipitation minus runoff without considering TWSC). Results show that the regional annual ET ranges from 417.7 mm/yr to 831.5 mm/yr in the nine exorheic catchments based on the water balance equation. The impact of ignoring TWSC on calculating ET is notable, as the root mean square errors (RMSEs) of annual ET between ETWB and ETPQ range from 12.0–105.8 mm/yr (2.6–12.7% in corresponding annual ET) among the exorheic catchments. We also compared the estimated regional ET with other ET products. Different precipitation products are assessed to explain the inconsistency between different ET products and regional ET from a water balance perspective. The RMSEs between ET estimates from Gravity Recovery and Climate Experiment (GRACE) and ET from land surface models can be reduced if the deviation of precipitation forcing data is considered. ET estimates from Global Land Evaporation Amsterdam Model (GLEAM) can be improved by reducing the uncertainty of precipitation forcing data in three semiarid catchments. This study emphasizes the importance of considering TWSC when calculating the regional ET using a water balance equation and provides more accurate ET estimates to help improve modeled ET results.

Global or regional mean evapotranspiration (ET), calculated as the difference between observed precipitation (P) and runoff (R), has been widely used as the standard method to investigate the long‐term variability of ET and evaluate hydrological and climate models. The increasing number of reservoirs built in China has led to a considerable amount of water storage, which could significantly alter regional water budgets. This change in terrestrial water storage (ΔS) because of the newly built reservoirs reduces the observed R but does not directly translate into ET. The present study is the first to quantify this reservoir effect on the estimated ET at the national and basin scale from 1997 to 2014 in China. The results show that the reservoir total storage capacity in China increased by 0.38 × 1012 m3 from 1997 to 2014. If this change in ΔS is not considered, a significant increase in the calculated ET of 4.2% per decade is derived. However, after this change in ΔS is taken into account, the calculated trend of ET decreases to almost zero for the period 1997 to 2014, which is consistent with the negligible changes in the determining factors for ET, including precipitation, surface incident solar radiation, and air temperature. The impact of reservoirs and the determining factors of ET are further explored in six major river basins of China, which confirmed our conclusions at the national scale. This study indicates that the impact of ΔS due to reservoir construction on calculated ET trends must be considered.

Abstract:The central route of the South-North Water Transfer Project (CTP) is designed to divert approximately 9.5 billion m 3 of water per year from the Han River, a major tributary of the Yangtze River, to the Hai River basin in the north China. The main purpose of this study is to assess the impact of CTP on groundwater table in the Hai River basin. Our study features a large-scale distributed hydrological model that couples a physically based groundwater module, which is sub-basin-based, with a conceptual surface water module, which is grid-based. There are several grids in each sub-basin and water exchange among grid that are considered. Our model couples surface water module and groundwater module and calculates human water use at the same time.The simulation results indicate that even with the water supply by CTP, the groundwater table will continue to decline in the Hai River basin. However, the CTP water can evidently reduce the decline rate, helping alleviate groundwater overexploitation in Hai River region.