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Quantitatively evaluation of satellite precipitation and potential evapotranspiration products with the high resolution, wide coverage and dynamic continuity is an important foundation for drought monitoring over mainland China. This paper examined the accuracy of products and the utility of drought monitoring using the newly released long-term (more than 30 years) satellite precipitation products (climate hazards group infrared precipitation with station, CHIRPS) data version 2.0 and potential evapotranspiration products (global land-surface evaporation: the Amsterdam methodology, GLEAM) dataset. We selected standardized precipitation evapotranspiration index (SPEI) and six statistical and classification measures indexes to evaluate accuracy and the utility of CHIRPS and GLEAM-Ep (potential evapotranspiration derived from GLEAM), with China Gauge-based Precipitation Daily Analysis dataset (CGDPA) and potential evapotranspiration calculated by Penman-Monteith (PM-Ep) as evaluation reference data sets. The results showed that CHIRPS and GLEAM-Ep performed well in eastern and southwest of China. However, their performance in western China was uncertain due to the sparsity of meteorological stations. SPEIs (SPEI value calculated by the CHIRPS and GLEAM-Ep) had a good performance on drought monitoring in eastern and southwestern China. Values of correlation coefficient (CC) between SPEIs and SPEIm (SPEI value calculated by the CGDPA and PM-Ep) were more than 0.6 in southeastern China, southwestern China, the middle and lower reaches of the Yangtze River region and northern China, especially in relatively humid areas, which the correlation coefficient values were more than 0.7 and the root mean-squared error (RMSE) values were less than 0.8. In order to further evaluate the performance of SPEIs in drought monitoring at spatial and temporal scales, the SPEIs3 (SPEIs at three-month scale) and SPEIm3 (SPEIm at three-month scale) in southeastern China, southwestern China, the middle and lower reaches of the Yangtze River region and northern China were compared. SPEIs3 had a better simulation effect on the evolution process of the ratio of drought area in those regions during1981-2016. And the success ratio of simulating drought duration was about 0.93, 0.57, 0.71 and 0.81, respectively. Moreover, SPEIs3 displayed a high accuracy over the four regions in capturing drought, which was the spatial distribution of typical drought events on specific month. In conclusion, SPEI based on long-term CHIRPS and GLEAM-Ep could be applied to monitor and evaluate drought in eastern and southwestern China. This paper can provide reliable reference for monitoring and warning of drought events and water resources management in those regions. [ABSTRACT FROM AUTHOR]

Biological soil crusts are fundamental components and surface landscape in arid regions, and biogeochemical process also depends on them. However, biological soil crusts stoichiometry remains largely unknown in the desert region of Northern China. The influences of precipitation on biological soil crusts stoichiometry is also lacking in desert steppe. This paper aims to investigate the effects of precipitation on the stoichiometry of biological soil crusts in desert steppe. This field study was conducted at Dashuikeng Grassland Research Station, Yanchi County (106°58′E, 37°24′N, average elevation, 1 560 m), Ningxia Hui Autonomous Region, China. This region covers a large ecosystem of desert steppe that characterized by low rainfall and uneven precipitation, along the southwest edge of the Mu Us Sandy Land. In the study desert steppe area on the southeastern margin of the Tengger Desert, the average annual precipitation was only 298.3 mm during the 60 years from 1959 to 2019. The precipitation was regulated by the measurement of artificial rain using rainwater shed and sprinkler irrigation technologies, in order to evaluate precipitation effects on the biological soil crusts in desert steppe compared with natural precipitation. 28 precipitation treatments (6 m×6 m) were set up at the test station in early March 2018, where 3 m wide buffer zone was designed between each time. Control conditions of precipitation were designed via the shelter and sprinkler irrigation system, including 7 precipitation treatments, natural precipitation (CK), drought (1/2 reduction in precipitation, DW1/2 treatment, 1/3 reduction in natural precipitation, DW1/3 treatment, 1/4 reduction in precipitation, DW1/4 treatment), and increasing precipitation (1/2 increase in natural precipitation, IW1/2 treatment, 1/3 increase in natural precipitation, IW1/3 treatment, 1/4 increase in natural precipitation, IW1/4 treatment). Each treatment has 4 spares for the reproductivity. In the same period, small weather stations were set up in the test area. TRIME-PICO TDR Portable Soil Moisture Meter (made in Germany) was used for the data collection of precipitation in the soil water depth of 10 cm. Carbon (C), nitrogen (N) and phosphorus (P) contents of biological soil crusts were measured to examine the C: N: P stoichiometry and its driving factors. Three findings can be achieved: 1) Water-reducing treatment was beneficial to the enrichment of C, N and P in the crust. DW1/4 treatment and natural precipitation treatment posed significant effects on the C content in the crust layer and underlying soil. The water-reducing treatment can reduce the N level of the crust, while increase the N level of the underlying surface. The content of P in the crust layer was the lowest under DW 1/3 treatment, whereas the content of P in the underlying surface reached the peak under DW 1/2 treatment; 2) Natural rainfall and increased precipitation can significantly improve the underlying surface C: N and C: P. There was a reduction of N: P in the crust layer and its underlying surface; 3) Suitable soil moisture conditions promoted the accumulation of SMBC (Soil Microbial Biomass Carbon) and SMBN (Soil Microbial Biomass Nitrogen) on the crust layer and underlying surface, while excessive rainfall caused the loss of soil nutrients, which was not conducive to the accumulation of SMBC and SMBN. The relatively dry soil environment was conducive to the enrichment of soil carbon and nitrogen in the crust layer, provided more nutrients for soil microbial respiration, and was conducive to the accumulation of SMBC and SMBN. In short, the C: N: P stoichiometry of biological soil crusts and underlying surfaces had different responses to precipitation in the desertification areas of northern China. [ABSTRACT FROM AUTHOR]

Water Use Efficiency (WUE) refers to the ratio of water used in plant metabolism over water lost in evapotranspiration, indicating carbon-water coupling in terrestrial ecosystem and its response to global change. It is of great significance to clarify the long-term variation characteristics and influencing factors of WUE for the study of carbon and water cycles and the rational utilization of water resources. This study aims to estimate the vegetation WUE of a research site, particularly on the annual and interannual variation characteristics of WUE, and to establish the response relationship between WUE and key meteorological factors. The data used in this paper mainly include the flux and meteorological information from eight sites in China from January 2003 to December 2010. Unified quality control and interpolation methods were then used to pre-process the flux data. The daily flux and meteorological data were combined into 8-day data sets in each site. Pearson coefficient was used to analyze the correlation between vegetation WUE and Gross Primary Productivity (GPP), ET, average temperature, precipitation, and relative humidity factors. The characteristics and influencing factors of WUE were analyzed and compared in different ecosystem. The results showed that: 1)WUE fluctuated greatly in the whole year without obvious regularity in Qianyanzhou, Xishuangbanna and Dinghushan sites which locate in the tropical monsoon climate region, while WUE showed obvious seasonal variation characteristics in the other five sites, all of which increased significantly from April to July, and reached the maximum during the peak period (July to August), and then WUE decreased gradually from August to October. From November to February of the following year, WUE reached zero. 2) From 2003 to 2010, the annual WUE of alpine meadow (Damxung) was the lowest (0.18 g/kg), whereas, that of tropical rainforest (Xishuangbanna) was the highest (4.20 g/kg). The WUE increased annually in the grassland (Inner Mongolia), broad-leaved evergreen forest (Dinghu Mountain), farmland (Yucheng), alpine meadow (Damxung), and alpine meadow (Haibei), whereas, the decreasing trend occurred in the coniferous forest (Qianyanzhou), tropical rainforest (Xishuangbanna), deciduous broad-leaved and coniferous mixed forests (Changbai Mountain). 3) In the 8-day time scale, there was positively correlation between temperature and WUE in alpine meadow, farmland and grassland ecosystem, whereas there was the negatively correlation between temperature and WUE in forest ecosystem. And the negative correlation between WUE and temperature in coniferous forest ecosystem (R=-0.607, P<0.01) was higher than that in evergreen broad-leaved forest and coniferous broad-leaved mixed forest ecosystem. Compared with forest and farmland ecosystem, WUE in alpine meadow and grassland ecosystem had a higher correlation with relative humidity and precipitation; 4) In different ecosystem, the various approaches were proposed to enhance WUE of terrestrial ecosystem for the sustainable development of agriculture, forestry and animal husbandry. Soil management regulation and canopy pruning can improve water use efficiency in the case of forest ecosystem. In farmland ecosystem, water use efficiency can be elevated from irrigation mode and crop breeding. In alpine meadow and grassland ecosystem, man-made grass, rest grazing and area rotation grazing can be used to enhance grassland carbon sink, further to improve water use efficiency. The findings can provide promising potentials to alleviate water shortage against the background of global warming. [ABSTRACT FROM AUTHOR]

There is an obvious gap between China's current irrigation water use efficiency and the world's advanced level for that of China is only 0.50, whereas that of world's advanced level reaches 0.7-0.8. Therefore, saving water resources, improving agricultural irrigation water efficiency, and ensuring the irrigation efficiency will be a long-term strategic task in the future of China. The purpose of this paper was to make a comprehensive evaluation for water use efficiency of Yellow River irrigation area based on flow-tracing and multiple weights method. In order to make a good comprehensive evaluation for water using efficiency, an open index-evaluation system including 19 deterministic index and 3 sub-systems based on irrigation flow-tracing method. Then, the improved fuzzy evaluation model was constructed based on multiple layer-weight determination method by making use of multi-objective and multi-level system. In the first layer (input layer), the index weight was confirmed by calculating entropy-weight-vector, and in the second layer (criterion layer), the sub-system weight was confirmed by the entropy-weight-vector method, equal-weight method and experience weight method, respectively for multi-layer weights. Finally, obtaining data and comparing different weights from the evaluation results was carried out by the fuzzy evaluation model. The paper took Sanyizhai Irrigation Area in lower reaches of the Yellow River as a case study. Sanyizhai Irrigation Area is located in the eastern plain of Henan Province (34°52N, 144°44E), north of the Yellow River. Sanyizhai Irrigation Area was founded in 1958, and it involves 18 counties scattered in Kaifeng, Shangqiu and Heze in Henan Province, and Shandong Provinces as well. Up to now, the water-diverting capacity of Sanyizhai Irrigation Area is about 150 m3/s, and irrigation area covers 9 counties(districts) mainly in the eastern part of Henan province, that is: Kaifeng, Lankao and Qi counties of Kaifeng City, Minquan County, Ningling County, Suiyang District, Liangyuan District, Sui County and Yucheng County of Shangqiu City respectively. The total land area of Sanyizhai Irrigation Area reaches 4 344.2 km2 and the total cultivated area is 2 701.42 km2. The paper took 10 years data from 2005 to 2014 of Sanyizhai Irrigation Area as a case study to make a comprehensive evaluation for water use efficiency. The 3 kinds of weight was used for the calculation. The results showed that: the first entropy-weight-vector weight was 0.307, 0.348, 0.345, the second equal-weight was 0.333, 0.333, 0.334, and the third subjective weight was 0.400, 0.200, 0.400. The evaluation result presented a general identical trend and showed that weight-influence was very limited for the evaluation result. According to the evaluation result, the irrigation water effect in 2013 was optimal among 10 years with average value 0.993 by comprehensive evaluation. Meanwhile, this evaluation results were in conformity with the actual situation of Sanyizhai Irrigation Area. In 2013 the rainfall and groundwater is relatively small, whereas the practical diverted irrigation intake and irrigation area has kept high level, which has ensured irrigation effect of and crop-harvest. According to the evaluation value of second layer, the dynamic variation process about engineering factors and management factors could be seen clearly, which showed that it kept a low-level development before 2007 and entered into a higher level development after 2009, so it could help us find the existing problems in irrigation process and provides data basis and technical support for the scientific planning and sustainable development of Yellow River Irrigation Area. [ABSTRACT FROM AUTHOR]