Rainfall is one of the most basic meteorological and hydrological elements. Quantitative rainfall estimation has always been a common concern in many fields of research and practice, such as meteorology, hydrology, and environment, as well as being one of the most important research hotspots in various fields nowadays. Due to the development of space observation technology and statistics, progress has been made in rainfall quantitative spatial estimation, which has continuously deepened our understanding of the water cycle across different space-time scales. In light of the information sources used in rainfall spatial estimation, this paper summarized the research progress in traditional spatial interpolation, remote sensing retrieval, atmospheric reanalysis rainfall, and multi-source rainfall merging since 2000. However, because of the extremely complex spatiotemporal variability and physical mechanism of rainfall, it is still quite challenging to obtain rainfall spatial distribution with high quality and resolution. Therefore, we present existing problems that require further exploration, including the improvement of interpolation and merging methods, the comprehensive evaluation of remote sensing, and the reanalysis of rainfall data and in-depth application of non-gauge based rainfall data.

Rainfall occurs frequently in South China and results in recurring of drainage/discharge of nitrogen and phosphorus-rich water from paddy fields, which may cause serious non-point source pollution of receiving waters such as rivers. Moreover, time intervals between individual rainfall events are short (often only several days). Thus, not only is the treatment of discharge water needed, but a more rapid form of treatment is desired as well. On the basis of the literature, constructed wetlands could remove nitrogen and phosphorous from paddy field drainage/outflow, and effective microorganisms (EM) could also be added to enhance the removals. A field experiment was conducted to demonstrate the wetland effectiveness and EM enhancement. The experiment was conducted from June to October in 2016. By applying EM to constructed wetlands, after 8 days, concentrations of total nitrogen (TN), ammonium nitrogen (${\mathrm{NH}}_4^{ +}$-N), nitrate nitrogen (${\mathrm{NO}}_3^{ -}$-N), and total phosphorus (TP) were reduced by 88%, 91%, 89%, and 50%, respectively. Within the first 4 days, TN and TP concentrations were reduced by 78% and 40%, respectively, with EM application, in comparison to 50% and 20%, respectively, without EM application, representing additional respective reductions of 28% and 20% by applying EM. The results from the field experiment indicated a significant improvement of phosphorus and nitrogen removals by applying effective microorganisms.

In recent decades, strong human activities have not only brought about climate change including both global warming and shifts in the weather patterns but have also caused anomalous variations of hydrological elements in different basins all around the world. Studying the mechanisms and causes of these hydrological variations scientifically is the basis for the management of water resources and the implementation of ecological protection. Therefore, taking the Yongding River mountain area as a representative watershed in China, the changes of different observed and simulated hydro-meteorological variables and their possible causes are analyzed on an inter-annual scale based on ground based observations and remotely sensed data of hydrology, meteorology and underlying surface characteristics from 1956 to 2016. The results show that the annual natural runoff of Guanting hydrological station in the main stream of the Yongding River, Cetian hydrological station and Xiangshuibao hydrological station in the tributary of the Yongding River all have a significant decreasing trend and abrupt changes, and all the abrupt change points of the annual natural runoff series of the three hydrological stations appear in the early 1980s. On the inter-annual scale, the water balance model with double parameters is unable to effectively simulate the natural surface runoff after the abrupt change points. The annual average precipitation after the abrupt change points decreases by no more than 10%, compared with that before the abrupt change points. However, the precipitation from July to August, which is the main runoff-production period, decreases by more than 25%, besides the intra-annual temporal distribution of precipitation becoming uniform and a significant decrease in effective rainfall, which is the source of the runoff. Meanwhile, the NDVI in the basin show an increasing trend, while the groundwater level and land water storage decrease significantly. These factors do not lead only to the continuous reduction of the annual natural runoff in the Yongding River mountain area from 1956 to 2016, but also result in significant changes of the hydro-meteorological relationship in the basin.

Based on the long series of gauge rainfall data from 1979 to 2015, the performance of Multi-Source Weighted-Ensemble Precipitation (MSWEP) precipitation dataset in the Zhoushan Archipelago and its surrounding sea area in Southeast China was evaluated from a variety of perspectives, and then the Cressman scheme was used to merge MSWEP with surface gauge measurements. It was found that at the spatial scale of 0.1° × 0.1°, MSWEP correctly detected most of the daily rainfall events in the study area. The surface precipitation was generally underestimated, with a relative deviation no more than 10%, but there was a fairly high miss reporting on heavy precipitation. The performance of MSWEP is also obviously characterized with seasonal fluctuation. Compared with the gauge records interpolation results, the accuracy statistics of rainfall dataset generated by merging MSWEP with gauge observations is improved to a certain degree. Especially its comprehensive identification ability of the dry and wet state for daily precipitation has been obviously raised. In addition, the merged data has the mixed characteristics of rain gauge observations and MSWEP in spatial structure. This paper has deepened the understanding of the performance of MSWEP in islands and sea areas, and also strengthened the understanding of the marginal effect of merging gauge data with MSWEP, even other global precipitation datasets.

Reference precipitation (RP) serves as a benchmark for evaluating the accuracy of precipitation products; thus, the selection of RP considerably affects the evaluation. In order to quantify this impact and provide guidance for RP selection, three interpolation methods, namely inverse distance weighting (IDW), ordinary kriging (OK), and geographical weighted regression (GWR), along with six groups of station densities, were adopted to generate different RPs, based on the super-high-density rainfall observations as true values, and we analyzed the errors of different RPs and the impacts of RP selection on the assessment of GPM precipitation products. Results indicate that the RPs from IDW and GWR both approached the true values as the station density increased (CC > 0.90); while the RP from OK showed some differences (CC < 0.80), it was similar to GWR when the station density was low, but the accuracy improved at first and then worsened as the station density continued to increase; the evaluation results based on different RPs showed remarkable differences even under the same conditions; when the average distance between rainfall gauges that were utilized to generate RPs was below the medium value (i.e., d < 20 km), the evaluation based on RP derived from IDW and GWR was close enough to that based on the true precipitation, which indicates its feasibility in evaluating satellite precipitation products.

This study investigates the urbanization of Taihu Basin and its influence on Satellite Pour l’Observation de la Terre (SPOT)-Normalized Difference Vegetation Index (NDVI). The correction model of the Defense Meteorological Satellite Program-Operational Linescan System (DMSP-OLS) of nighttime images was built to extract the dynamics of urban expansion. Tempo-spatial correlations between a vegetation index and nighttime light intensity are discussed to quantitatively assess the urbanization effect. The results show that Taihu Basin is in a period of rapid urbanization. Urban expansion is developing not only surrounding the city center circle but also along the main traffic arteries and rivers, which show a linear expansion resulting in an urban agglomeration. Under the influence of urbanization, the NDVI shows a slight decrease, and there is a significant negative tempo-spatial correlation in the urban areas of the eastern watershed between NDVI and nighttime light intensity, which are predominantly...